| 1. |
- Akhavan Attar, Ali, et al.
(författare)
-
High Strength-Elongation Balance in Warm Accumulative Roll Bonded AA1050 Sheets
- 2022
-
Ingår i: Metals and Materials International. - : Springer. - 1598-9623 .- 2005-4149. ; 28, s. 346-360
-
Tidskriftsartikel (refereegranskat)abstract
- Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter (UTS×El.ε) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.
|
|
| 2. |
- Akhavan Attar, Ali, et al.
(författare)
-
Improving the fracture toughness of multi-layered commercial pure aluminum via warm accumulative roll bonding
- 2021
-
Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 116, s. 3603-3617
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the fracture toughness of the multi-layered commercial pure aluminum samples (AA1050) prepared by warm accumulative roll bonding (WARB) was investigated for the first time. Based on the ASTM E561 standard, the R-curve method was utilized to measure the plane stress fracture toughness. Compact tension (CT) samples were prepared from the sheets that were processed by different ARB cycles. Mechanical properties, microstructure, and fracture surfaces of the CT samples were studied by uniaxial tensile test, electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM), respectively. By increasing the number of WARB cycles, fracture toughness increased; after five cycles, 78% enhancement was observed compared to the pre-processed state. A correlation was seen between the fracture toughness variations and ultimate tensile strength (UTS). WARB enhanced UTS up to 95%, while the grain size showed a reduction from 35 to 1.8 μm. Measured fracture toughness values were compared with the room temperature ARB outcomes, and the effective parameters were analyzed. Fractography results indicated that the presence of tiny cliffs and furrows and hollow under fatigue loading zones and shear ductile rupture in the Quasi-static tensile loading zone.
|
|
| 3. |
- Ashrafi, Hamid, et al.
(författare)
-
Damage Micromechanisms in Friction Stir-Welded DP600 Steel during Uniaxial Tensile Deformation
- 2022
-
Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 31, s. 10044-10053
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, damage initiation micromechanisms in friction stir-welded DP600 steel sheets during tensile deformation were studied by scanning electron microscopy (SEM) and electron backscatter diffraction. For this purpose, DP600 steel was welded using friction stir welding with two combinations of rotational and transverse speed, to prepare joints with low and high heats. Microhardness measurements on the cross section of the weldments revealed the formation of a softened zone in the HAZ as a result of the tempering of the martensite, which led to the localization of strain and failure during the tensile testing. SEM observations on the cross section of tensile tested specimens showed that ferrite–martensite interface decohesion and martensite fracture are the main void nucleation mechanisms in the DP600 steel. For the sample welded with low heat input, ferrite–martensite interface decohesion started at higher strains compared to the DP600 steel. A new void initiation mechanism including plastic deformation of tempered martensite, necking, separation of martensite fragments and formation of a void between the separated segments was also suggested for this sample. For the sample welded with high heat input, formation of void at the ferrite–cementite interface was the main void nucleation mechanism and ferrite–martensite interface decohesion was an inactive mechanism.
|
|
| 4. |
- Ashrafi, Hamid, et al.
(författare)
-
Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension
- 2020
-
Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 33, s. 299-306
-
Tidskriftsartikel (refereegranskat)abstract
- The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.
|
|
| 5. |
- Babu, Bijish, Tec. Lic. 1979-, et al.
(författare)
-
Dislocation density based plasticity model extended to high strain rate deformation of Ti-6Al-4V
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- One of the main challenges in the simulation of machining is accurately describing the material behavior during severe plastic deformation at strain rates ranging six orders of magnitude and temperature between room temperature to nearly melting temperature. High strain rate measurements are performed using Split-Hopkinson Pressure Bar (SHPB) technique at a range of temperatures. The temperature change during deformation is included by computing the plastic work converted to heat energy. A physics-based material model published earlier (Babu and Lindgren, 2013) is extended in this paper to include the high strain rate mechanisms of phonon and electron drag. Characterization of the microstructure is performed using Electron Backscatter Diffraction (EBSD), and a novel method is proposed in this work to quantify the extent of globularization which is compared with model predictions.
|
|
| 6. |
- Bjurenstedt, Anton, 1979-, et al.
(författare)
-
The effect of Fe-rich intermetallics on crack initiation in cast aluminium : an in-situ tensile study
- 2019
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 756, s. 502-507
-
Tidskriftsartikel (refereegranskat)abstract
- To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites.
|
|
| 7. |
- Bogdanoff, Toni, et al.
(författare)
-
A simple procedure to assess the Complete Melt Quality in aluminium castings : implementation in a die-casting and a rheo-casting
- 2024
-
Ingår i: International Journal of Cast Metals Research. - : Taylor & Francis. - 1364-0461 .- 1743-1336. ; 37:1, s. 71-79
-
Tidskriftsartikel (refereegranskat)abstract
- A new simple approach was developed to assess the Complete Melt Quality of aluminium cast alloys throughout the production line. The approach relies on the concurrent use of reduced pressure tests (RPT) and tensile tests at each station in the production line when the melt is transferred and/or processed. These tests can be used to determine the source of melt-related problems in the production line. Two case studies from the procedure of both an aluminium die-casting and a rheo-casting plant showed that melts were significantly damaged in the tower furnace and got progressively more damaged through the production line proven by the RPT, tensile test, and fracture surface analysis results.
|
|
| 8. |
- Bogdanoff, Toni, et al.
(författare)
-
On the combined effects of surface quality and pore size on the fatigue life of Al–7Si–3Cu–Mg alloy castings
- 2023
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 885
-
Tidskriftsartikel (refereegranskat)abstract
- This study has aimed to determine the effects of surface quality and pore size, obtained by different levels of hydrogen content of the liquid metal, on the fatigue behavior of an Al–7%Si–3%Cu–Mg casting alloy. Three surface conditions have been studied: as-cast rough, as-cast smooth, and standard machined and polished surface. The S–N curves have shown that surface roughness and hydrogen content individually impact fatigue strength. Surprisingly, the fatigue strength of machined and polished samples, which aligns with standard testing practices, is significantly reduced, compared to other conditions. Fatigue cracks have been observed to initiate at the pores just below the as-cast surface or on the machined surfaces. In all cases, pores have been observed to be surrounded by bifilms. Moreover, hydrogen content and roughness of the as-cast surface have been found to interact to determine the fatigue performance. These findings necessitate a re-evaluation of fatigue testing procedures for cast aluminum components.
|
|
| 9. |
- Bogdanoff, Toni, et al.
(författare)
-
On the Effectiveness of Rotary Degassing of Recycled Al-Si Alloy Melts : The Effect on Melt Quality and Energy Consumption for Melt Preparation
- 2023
-
Ingår i: Sustainability. - : MDPI. - 2071-1050. ; 15:6
-
Tidskriftsartikel (refereegranskat)abstract
- The effectiveness of rotary degassing on the defect formation and mechanical properties of the final casting of aluminium alloy EN AC 46000 was investigated, along with its impact on the energy consumption in the casting furnace. In the melt preparation prior to casting, the molten metal is usually transported from the melting furnace to the casting furnace with rotary degassing as a cleaning procedure. Under the conditions of this specific study, negligible degradation was observed in the mechanical properties of the final cast component in an aluminium EN AC 46000 alloy after removing the rotary degassing step in the process. Furthermore, removing the rotary degassing step led to a reduced temperature drop in the melt, thus minimizing the need for reheating (energy consumption) by up to 75% in the casting furnace. The reduced energy consumption was up to 124,000 kWh in yearly production in a 1500 kg casting furnace. The environmental impact showed a similar to 1500 kg reduction in CO2 for one 1500 kg electrical casting furnace in a year.
|
|
| 10. |
- Bogdanoff, Toni, et al.
(författare)
-
On the secondary cracks during crack propagation in an Al-Si-Cu-Mg alloy : An in-situ study
- 2023
-
Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 203
-
Tidskriftsartikel (refereegranskat)abstract
- During in situ cyclic testing of hot isostatically pressed and heat-treated Al-5Si-0.5 Mg-1Cu alloy castings, cracks were observed to open up in places far away from the area of stress concentration. Cyclic testing was interrupted to assess these cracks. Analysis showed that these cracks originated from oxide bifilms that were entrained in the liquid state. Moreover, Si and Fe-rich intermetallics were observed to have precipitated on these bifilms. These finding makes it necessary to re-evaluate how damage is interpreted in mechanical studies. Entrainment damage, which takes place in the liquid state, may remain invisible in non-destructive inspection and can significantly affect fatigue properties when bifilms open up under low tensile stresses and present the propagating crack a path of low resistance during propagation.
|
|
| 11. |
- Bogdanoff, Toni, et al.
(författare)
-
Prototyping of a high pressure die cast al-si alloy using plaster mold casting to replicate corresponding mechanical properties
- 2019
-
Ingår i: Minerals, Metals and Materials Series. - Cham : Springer. - 9783030058630 - 9783030058647 ; , s. 435-442
-
Konferensbidrag (refereegranskat)abstract
- Prototyping prior high pressure die casting (HPDC) is used for product/mold design optimization. Plaster mold casting is a cost-efficient prototyping technique providing good surface quality and dimension accuracy, similar to HPDC components. However, the corresponding mechanical properties of a component produced with these two methods are diverging significantly, mainly due to differences in the cooling rate. This work presents a procedure to optimize the plaster mold casting for prototyping to replicate mechanical properties of a commonly used Al-Si alloy (A380). Two commercial alloys with compositions close to the A380 alloy (A356.0 and A360.2) were used. Yield strength was considered as the main design criteria, thus the target mechanical property. Tensile testing results showed that with an optimized T6 heat treatment, not only the yield strength, but also ultimate tensile strength and elongation correspond well to the properties in the HPDC component.
|
|
| 12. |
- Bogdanoff, Toni, et al.
(författare)
-
The complex interaction between microstructural features and crack evolution during cyclic testing in heat-treated Al–Si–Mg–Cu cast alloys
- 2021
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 825
-
Tidskriftsartikel (refereegranskat)abstract
- The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.
|
|
| 13. |
- Bogdanoff, Toni
(författare)
-
The effect of microstructural features, defects and surface quality on the fatigue performance in Al-Si-Mg Cast alloys
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is driving industry to manufacture lighter components to reduce carbon dioxide (CO2) emissions. Promising candidates for achieving this are aluminium-silicon (Al-Si) cast alloys, which offer a high weight-to-strength ratio, excellent corrosion resistance, and good castability. However, understanding variations in the mechanical properties of these alloys is crucial to producing high-performance parts for critical applications. Defects and oxides are the primary reasons cast components in fatigue applications are rejected, as they negatively impact mechanical properties.A comprehensive understanding of the correlation between fatigue performance and parameters such as the α-aluminium matrix, Al-Si eutectic, surface roughness, porosities, hydrogen content, oxides, and intermetallic phases in Al-Si castings has not been reached.The research presented in this thesis used state-of-the-art experimental techniques to investigate the mechanical properties and crack-initiation and propagation behaviour of Al-Si-Mg cast alloy under cyclic loading. In-situ cyclic testing was conducted using scanning electron microscopy (SEM) combined with electron back-scattered diffraction (EBSD), digital image correlation (DIC), and focused ion beam (FIB) milling. These techniques enabled a comprehensive study of parameters affecting fatigue performance, including hydrogen content, surface roughness, oxides, and intermetallic phases. More specifically, we investigated the effect of melt quality, copper (Cu) content, oxide bifilms, surface quality, and porosity.The increased Cu concentration in heat-treated Al-Si alloys increased the amount of intermetallic phases, which affected the cracking behaviour. Furthermore, oxide bifilms were detected at crack-initiation sites, even in regions far away from the highly strained areas. Si- and Iron (Fe)-rich intermetallics were observed to have precipitated on these bifilms. Due to their very small size, these oxides are generally not detected by non-destructive inspections, but affect mechanical properties because they appear to open at relatively low tensile stresses. Finally, Al-Si alloy casting skins showed an interesting effect in terms of improving fatigue performance, highlighting the negative effect of surface polishing for such alloys.
|
|
| 14. |
|
|
| 15. |
- Bogdanoff, Toni, et al.
(författare)
-
The impact of HIP process and heat treatment on the mechanical behavior of an Al-Si-Mg alloy component
- 2023
-
Konferensbidrag (refereegranskat)abstract
- Castings generally contain pores and defects that can have a detrimental impact on mechanical properties. The hot isostatic pressing (HIP) process is usually applied to reduce internal porosities, which improves the mechanical properties because of the closed porosities. Therefore, this study investigates the effect of the HIP process on the mechanical properties of sand casting A356 aluminum alloys. This investigation was performed in collaboration with Unnaryd Modell, Quintus Technologies, and IAC Ankarsrum. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIP process was examined using computed tomography scanning, in-situ cyclic testing, and scanning electron microscope. In the absence of large defects, the fatigue performance was improved. However, a significant variation in the result was found between the different conditions, whereas the coarser microstructure with larger porosities before the HIP process showed decreased ultimate tensile strength and elongation to failure. The samples tested under high cycle fatigue showed a reduced fatigue propagation zone in that the coarser microstructure. Moreover, large cleavage areas containing oxides in the fracture surfaces indicated that the HIP process closes all the porosities, but the oxide films are not creating a strong bonding. Furthermore, the samples tested under low cycle fatigue showed a difference in the crack propagation, whereas the coarser microstructure showed large cracks opened up away from the notch that assists the propagation leading to reduced fatigue life.
|
|
| 16. |
- Bogdanoff, Toni, et al.
(författare)
-
The impact of HIP process and heat treatment on the mechanical behaviour of an Al–Si–Mg alloy component
- 2024
-
Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.
|
|
| 17. |
- Bogdanoff, Toni, et al.
(författare)
-
The influence of copper addition on crack initiation and propagation in an Al–Si–Mg alloy during cyclic testing
- 2020
-
Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs.
|
|
| 18. |
- Bogdanoff, Toni
(författare)
-
The influence of microstructure on the crack initiation and propagation in Al-Si casting alloys
- 2021
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system.The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features.The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components.
|
|
| 19. |
|
|
| 20. |
- Conway, Patrick L. J., et al.
(författare)
-
High entropy alloys towards industrial applications : High-throughput screening and experimental investigation
- 2022
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 830
-
Tidskriftsartikel (refereegranskat)abstract
- Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co–Cr–Fe–Mn–Ni system was implemented to find ‘islands’ of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co10Cr12Fe43Mn18Ni17, reducing the material cost compared to the equiatomic alloy by ∼40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch's model was used to calculate the SSH in reported alloys in this study within the Co–Cr–Fe–Mn–Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.
|
|
| 21. |
- Di Egidio, G., et al.
(författare)
-
Dry sliding behavior of AlSi10Mg alloy produced by Laser-based Powder Bed Fusion : influence of heat treatment and microstructure
- 2023
-
Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 516-517
-
Tidskriftsartikel (refereegranskat)abstract
- The L-PBF AlSi10Mg alloy is widely used in the production of structural parts in the transportation sector. However, the high stresses caused by the severe operating conditions require an optimal combination of mechanical and tribological properties. This paper reports on the effect of optimized T5 heat treatment (direct artificial aging: 4 h at 160 °C) and novel T6 heat treatment (rapid solution: 10 min at 510 °C, followed by artificial aging: 6 h at 160 °C) on the tribological behavior of the L-PBF AlSi10Mg alloy. Dry sliding tests (ball-on-disk) were carried out using AlSi10Mg samples as rotating disks against an Al2O3 stationary ball. The optimized T5 led to the formation of a stable protective oxide layer well adherent on the worn surface, increasing the wear resistance of the alloy. In addition, the novel T6 improved wear resistance compared to conventional T6 due to microstructural refinement induced by shorter solutionizing. The sub-surface analysis of the wear tracks highlighted the higher cohesion between the more homogeneous and finer Si particles and the α-Al matrix, as well as the improved load-bearing support compared to the coarser microstructure induced by conventional T6. Therefore, the new T6 could be the optimal solution for high-performance components.
|
|
| 22. |
- Di Egidio, Gianluca, et al.
(författare)
-
Influence of Microstructure on Fracture Mechanisms of the Heat-Treated AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion
- 2023
-
Ingår i: Materials. - : MDPI. - 1996-1944. ; 16:5
-
Tidskriftsartikel (refereegranskat)abstract
- Few systematic studies on the correlation between alloy microstructure and mechanical failure of the AlSi10Mg alloy produced by laser-based powder bed fusion (L-PBF) are available in the literature. This work investigates the fracture mechanisms of the L-PBF AlSi10Mg alloy in as-built (AB) condition and after three different heat treatments (T5 (4 h at 160 °C), standard T6 (T6B) (1 h at 540 °C followed by 4 h at 160 °C), and rapid T6 (T6R) (10 min at 510 °C followed by 6 h at 160 °C)). In-situ tensile tests were conducted with scanning electron microscopy combined with electron backscattering diffraction. In all samples the crack nucleation was at defects. In AB and T5, the interconnected Si network fostered damage at low strain due to the formation of voids and the fragmentation of the Si phase. T6 heat treatment (T6B and T6R) formed a discrete globular Si morphology with less stress concentration, which delayed the void nucleation and growth in the Al matrix. The analysis empirically confirmed the higher ductility of the T6 microstructure than that of the AB and T5, highlighting the positive effects on the mechanical performance of the more homogeneous distribution of finer Si particles in T6R.
|
|
| 23. |
|
|
| 24. |
- Dini, Hoda, et al.
(författare)
-
Microstructural Scale Effects on Thermal Expansion Behaviour of Cast AZ91D
- 2015
-
Ingår i: Magnesium Technology 2015 - TMS 2015 144th Annual Meeting and Exhibition, Orlando, March 15-19, 2015. - Hoboken : John Wiley & Sons. - 9781119082439 ; , s. 361-365
-
Konferensbidrag (refereegranskat)abstract
- The effect of microstructure on thermal expansion of AZ91D cast alloy was studied. Samples with equiaxed grains and a controlled secondary dendrite arm spacing (SDAS) were fabricated using gradient solidification. SDAS was chosen to represent the range ofmicrostructural scale found in sand castings down to that of high pressure die casting. Optical microscopy and electron backscatter diffraction (EBSD) were used for microstructural characterization. The relation between thermal expansion and microstructuralscale of existing phases precipitated, in particular grain size, SDAS and fraction of Mg17Al12 was analyzed.
|
|
| 25. |
|
|
| 26. |
- Dini, Hoda, 1984-, et al.
(författare)
-
Optimization and validation of a dislocation density based constitutive model for as-cast Mg-9%Al-1%Zn
- 2018
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 710, s. 17-26
-
Tidskriftsartikel (refereegranskat)abstract
- A dislocation density-based constitutive model, including effects of microstructure scale and temperature, was calibrated to predict flow stress of an as-cast AZ91D (Mg-9%Al-1%Zn) alloy. Tensile stress-strain data, for strain rates from 10-4 up to 10-1 s-1 and temperatures from room temperature up to 190 °C were used for model calibration. The used model accounts for the interaction of various microstructure features with dislocations and thereby on the plastic properties. It was shown that the Secondary Dendrite Arm Spacing (SDAS) size was appropriate as an initial characteristic microstructural scale input to the model. However, as strain increased the influence of subcells size and total dislocation density dominated the flow stress. The calibrated temperature-dependent parameters were validated through a correlation between microstructure and the physics of the deforming alloy. The model was validated by comparison with dislocation density obtained by using Electron Backscattered Diffraction (EBSD) technique.
|
|
| 27. |
- Ghasemi, Rohollah, 1983-, et al.
(författare)
-
Abrasion resistance of lamellar graphite iron : Interaction between microstructure and abrasive particles
- 2018
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 120, s. 465-475
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on abrasion resistance of Lamellar Graphite Iron (LGI) using microscratch test under constant and progressive load conditions. The interactions between a semi-spherical abrasive particle, cast iron matrix and graphite lamellas were physically simulated using a sphero-conical indenter. The produced scratches were analysed using LOM and SEM to scrutinise the effect of normal load on resulting scratch depth, width, frictional force, friction coefficient and deformation mechanism of matrix during scratching. Results showed a significant matrix deformation, and change both in frictional force and friction coefficient by increase of scratch load. Furthermore, it was shown how abrasive particles might produce deep scratches with severe matrix deformation which could result in graphite lamella's coverage and thereby deteriorate LGI's abrasion resistance.
|
|
| 28. |
|
|
| 29. |
- Ghassemali, Ehsan, et al.
(författare)
-
Bulk Metal Forming Processes in Manufacturing
- 2014
-
Ingår i: Handbook of Manufacturing Engineering and Technology. - Berlin : Springer Berlin/Heidelberg. - 9781447149767
-
Bokkapitel (refereegranskat)
|
|
| 30. |
- Ghassemali, Ehsan, et al.
(författare)
-
Dead-zone formation and micro-pin properties in progressive microforming process
- 2011
-
Ingår i: ICTP 2011, 10th International Conference on Technology of Plasticity, Steel Research International: Special Edition, Aachen, DE, Sep 25-29, 2011. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 9783514007840 ; , s. 1014-1019
-
Konferensbidrag (refereegranskat)abstract
- A novel progressive microforming process that consisted of a two step operations, punching and blanking was studied. Micropins with diameter of 300 µm were manufactured from metal strip to cater for a set-up with good potential for mass production. Investigations showed that the microstructure contains some deformed zones surrounded by less-deformed zones or "dead-zones" which is unique to the progressive microforming process. The aim of this work was to understand the origin and evolution of the "dead-zones" in the microstructure of the final products during the progressive microforming process, and find a way to avoid this phenomenon. To do this, the microstructure of the 300 µm pins with punch diameters of 3.2 and 2.2 mm at different punch displacement was investigated experimentally and by simulation. Experimental observations showed that dead-zones appear just after starting the microforming process, which is due to the friction at the workpiece-die interface. This dead zone leaks into the die cavity as a result of work-piece compression. It was shown that the inhomogeneous mechanical properties could be significantly improved by selection of an appropriate punch.
|
|
| 31. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy : an in situ study
- 2018
-
Ingår i: Philosophical Magazine Letters. - : Taylor & Francis. - 0950-0839 .- 1362-3036. ; 98:9, s. 400-409
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy.
|
|
| 32. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Effect of cold-work on the Hall–Petch breakdown in copper based micro-components
- 2015
-
Ingår i: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 80, part A, s. 124-135
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of substructural dimensions on the mechanical properties of micro-pins produced by an open-die micro-extrusion/forging process were studied. Micro-pins of diameter 0.3 mm were manufactured from copper strips, having different initial grain sizes. Micro-compression tests on the micro-pins revealed no significant size effect, even if the number of grains over the diameter of the micro-pins falls below its critical value. However, relaxation of the as-formed substructure using recovery annealing led to a surprising drop in the flow stress of the micro-pins. This was explained and attributed to the number of subgrains over the diameter of the micro-pins, showing the important role of subgrains rather than grains in determining the mechanical properties.
|
|
| 33. |
- Ghassemali, Ehsan, et al.
(författare)
-
Experimental and Simulation of Friction Effects in an Open-Die Microforging/Extrusion Process
- 2014
-
Ingår i: Journal of Micro and Nano-Manufacturing. - : ASME Press. - 2166-0468 .- 2166-0476. ; 2:1, s. 011005-
-
Tidskriftsartikel (refereegranskat)abstract
- Friction effects during a progressive microforming process for production of micropins of various diameters were experimentally investigated and were analytically modeled, using a hybrid friction model. The response surface method and ANOVA analysis were used to generalize the findings for various pin diameters. Besides, it was shown that to get an accurate result in simulation, the friction model must be considered locally instead of a global friction model for the whole process. The effect of friction factor on the final micropart dimensions (the effect on the instantaneous location of the neutral plane) and the forming pressure were investigated. The results showed a reduction in the friction factor as die diameter increased. Following that, the optimum frictional condition to obtain the highest micropart aspect ratio was defined as the maximum friction on the interface between the die upper surface and the punch surface, together with a minimum friction inside the die orifice.
|
|
| 34. |
- Ghassemali, Ehsan, 1983-
(författare)
-
Forging of Metallic Parts and Structures
- 2022
-
Ingår i: Encyclopedia of Materials. - Oxford : Elsevier. - 9780128197332 ; , s. 129-143
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Even with the wide applications of many new and modern manufacturing technologies, metal forming processes are still in great demand in many industrial sectors, ranging from transportation to medical applications. In this article, the basic knowledge in metal forming and specifically forging, which is one of the most commonly used processes for metal component manufacturing, is summarized. The effect of material behavior on the forming processes is discussed in detail. The classical modeling techniques to describe the forming processes are briefly introduced, with a focus on the challenges in this area. Different categories of forging process such as open-die, closed-die or cold, warm and hot forging are explained. Advantages of forging processes such as near-net-shape characteristics, microstructural refinement during the process, and relative ease of post-processing for forged parts are elaborated. Main disadvantages of forging include possible oxidation during hot forging, limitation on material selection for forging (workability), and the related maintenance cost of the forging tools. Examples of parts and structures that can be produced by forging process are metallic tools for various applications ranging from household to aerospace sectors, where close tolerance and proper mechanical properties are expected.
|
|
| 35. |
- Ghassemali, Ehsan, et al.
(författare)
-
Friction effects during open-die micro-forging/extrusion processes : An upper bound approach
- 2014
-
Ingår i: Procedia Engineering. - : Elsevier. ; , s. 1915-1920
-
Konferensbidrag (refereegranskat)abstract
- In microforming processes it is preferred to not to use lubricants, due to their complex behavior in micro-scale. Nevertheless, using lubricants could increase the life time and decrease the required forming load. Thus, it is necessary to study and develop an analytical solution for different lubrication conditions in microforming processes. A previously studied upper bound model was modified in this study for various lubrication conditions in an open-die micro-forging/extrusion process. Two approaches were chosen for identifying the friction factor in the model: (i) global friction factor, (ii) localized friction factor. Comparison of the modeling results with the experimental showed the reliability of the second approach, providing a better fit.
|
|
| 36. |
- Ghassemali, Ehsan, et al.
(författare)
-
Friction Factor in a Progressive Microforming Process
- 2012
-
Ingår i: 7 <sup>th</sup> INTERNATIONAL CONFERENCE ON MICROMANUFACTURING.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the effect of global and localized friction factoron the material forming in the simulation is investigated. Tomatch the simulation and experimental results, a reverse engineeringmethod has been used to get the correct frictionfactor for the defined condition in the microforming process.The friction size effect in the progressive microformingprocess has also been addressed.
|
|
| 37. |
- Ghassemali, Ehsan, et al.
(författare)
-
Grain size and workpiece dimension effects on material flow in an open-die micro-forging/extrusion process
- 2013
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 582:10, s. 379-388
-
Tidskriftsartikel (refereegranskat)abstract
- The interactive effect of grain size and specimen dimensions on the material flow and microstructural evolution was studied in a progressive open-die microforming process. Particular interest was paid on the effect of the number of grains over the initial specimen thickness, on the evolution of the dead metal zone (DMZ) in the final micro-component's microstructure. Such a DMZ is deemed unfavorable for mechanical properties of the pin. Interestingly, experimental results revealed that the DMZ can be removed at the pin surface by increasing the initial grain size. This behavior was attributed to the role of the strain gradient on the deformation. In the aspects of the forming load and dimensional measurements of the final parts, there were no significant size-effects observed in this process. This is because the neutral plane, which demarcates the two directions of material flow in the open-die forging/extrusion process, determines the amount of material flow towards the die orifice, regardless of the initial grain size.
|
|
| 38. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Hall-Petch Equation in a Hypoeutectic Al-Si Cast Alloy : Grain Size vs. Secondary Dendrite Arm Spacing
- 2017
-
Ingår i: Procedia Engineering. - : Elsevier. ; , s. 19-24
-
Konferensbidrag (refereegranskat)abstract
- The Al-Si cast alloy family is widely used in the production of complex castings for various applications and known for its very good castability and high strength-to-weight ratio. However, early cracking under tensile loading is sometimes a limiting factor. Among other parameters, it is yet controversial whether grain boundaries are dominant strengthening factor in cast alloys, instead of dendrite/eutectic boundaries. This study presents the effect of secondary dendrite arm spacing (SDAS) and grain size on crack initiation and propagation of Al-Si cast alloys under tensile loading. The Al-10Si (wt.%) alloy with modified Si morphology was cast using inoculants (Al-5Ti-B master alloy) under different cooling rates to obtain a range of grain sizes (from below 138 μm to above 300 μm) and SDAS (6, 15 and 35 μm). Conventional tensile test as well as in-situ tensile test in a scanning electron microscope, equipped with an electron backscatter diffraction (EBSD) was carried out to understand the deformation mechanisms of the alloy. Observation of slip bands within the dendrites showed that in modified Si structure, the interdendritic (eutectic) area takes more portion of the strain during plastic deformation. Besides, only a few cracks were initiated at the grain boundaries; they were mostly initiated from dendrite/eutectic interface. All cracks propagated trans-granularly. Hall-Petch calculations also showed a strong relationship between SDAS and flow stress of the cast alloy. Although statistically correct, there was no physically meaningful relationship between the grain size and the flow stress. Nevertheless, formation of identical slip bands in each grain could be an evidence for the marginal effect of the grain size on the overall strength development of the alloy. Consequently, among other effects, the combinational dominant effect of SDAS and modest effect of grain size shall be considered for modification of the Hall-Petch equation for precise prediction of mechanical properties of cast alloys.
|
|
| 39. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
High-Throughput CALPHAD : A Powerful Tool Towards Accelerated Metallurgy
- 2022
-
Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 9
-
Forskningsöversikt (refereegranskat)abstract
- Introduction of high entropy alloys or multi-principal element alloys around 15 years ago motivated revising conventional alloy design strategies and proposed new ways for alloy development. Despite significant research since then, the potential for new material discoveries using the MPEA concept has hardly been scratched. Given the number of available elements and the vastness of possible composition combinations, an unlimited number of alloys are waiting to be investigated! Discovering novel high-performance materials can be like finding a needle in a haystack, which demands an enormous amount of time and computational capacity. To overcome the challenge, a systematic approach is essential to meet the growing demand for developing novel high-performance or multifunctional materials. This article aims to briefly review the challenges, recent progress and gaps, and future outlook in accelerated alloy development, with a specific focus on computational high-throughput (HT) screening methods integrated with the Calculation of Phase Diagrams (CALPHAD) technique. Copyright © 2022 Ghassemali and Conway.
|
|
| 40. |
- Ghassemali, Ehsan, et al.
(författare)
-
In-situ study of crack initiation and propagation in a dual phase AlCoCrFeNi high entropy alloy
- 2017
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 710, s. 539-546
-
Tidskriftsartikel (refereegranskat)abstract
- This study reports the effect of phase distribution on crack propagation in a dual phase AlCoCrFeNi high entropy alloy (HEA) under tensile loading. The alloy is characterized by the presence of a brittle disordered BCC phase that can be toughened by precipitation of a ductile FCC phase during homogenization heat treatment. The stress and strain partitioning between the two phases is of paramount importance to determine the mechanical response of this alloy. The as-cast alloy was subjected to homogenization at 1273 K for 6 h to prevent the formation of detrimental sigma phases and to precipitate the ductile FCC phase. In-situ tensile test in a scanning electron microscope with an electron backscatter diffraction facility was carried out to understand the micro-mechanisms of deformation of the alloy. Precipitation of the FCC phase at the BCC grain boundaries reflected the effect of the FCC phase on crack deflection and branching during propagation. The strain partitioning between the two phases and the evolution of misorientation distribution was investigated. It is observed that the presence of ductile FCC high entropy phase can impart good room temperature ductility to the brittle BCC phase. As there are very few investigations performed on the dual phase HEAs, a proper microstructural design can be be achieved and can be utilized to toughen the brittle HEAs.
|
|
| 41. |
|
|
| 42. |
- Ghassemali, Ehsan, et al.
(författare)
-
Microstructural Evolution in a Low Carbon Steel During Cold Rolling and Subsequent Annealing
- 2010
-
Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6177-6181
-
Tidskriftsartikel (refereegranskat)abstract
- Cold rolling with subsequent annealing of lath martensite structure could lead to the formation of nanostructures in low carbon steels. In the present work, the microstructural evolution of a 0.13% C steel during this process was studied. The specimens were austenitized at 950 °C followed by quenching in ice-brine to get martensitic structure. The quenched samples were aged at 200 °C for 30 min. These specimens were cold rolled up to 90% reduction in thickness without any intermediate annealing and then annealed at the temperatures from 400 to 600 °C. Scanning and transmission electron microscopy and color metallography was used to investigate the microstructure. Microscopic investigations showed that a multiphase nanostructure composed of equiaxed ferrite grains with the mean grain size of about 188 nm and small blocks of tempered martensite can be achieved under annealing at 400 °C for 90 min. Formation of the nanostructure was discussed from the viewpoint of characteristics of the martensite starting structure. Fragmentation of martensite lathes in cold rolling stage play an important role on recrystallization at annealing stage to get the ultrafine structure.
|
|
| 43. |
- Ghassemali, Ehsan, et al.
(författare)
-
Microstructure versus substructure size effect
- 2016
-
Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X. - 9780735414273 ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- In metal deformation, size effect is generally attributed to the interactive effect of grain size and specimen dimension. This work shows, however, that relative substructure dimensions should also be considered. Micro-compression tests on the micro-pins having different grain sizes revealed no significant size effect with respect to the mechanical behavior, even if the number of grains over the diameter of the micro-pins falls below its critical value. To justify the reason laying under this fact, a recovery annealing cycle was applied on the micro-pins to change the substructure properties without altering the mean grain size. A surprising drop in the flow stress of the recovery-annealed micro-pins implied the importance of considering subgrain size rather than grain size over the diameter of component for the size effect investigation.
|
|
| 44. |
- Ghassemali, Ehsan
(författare)
-
Nanoporous Titania-Coated Alumina Membranes: Sol–Gel Synthesis and Characterisation
- 2010
-
Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6222-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, nanoporous titania top layers were deposited by dip-coating process on microporous α-alumina substrates using the sol–gel process. The alumina substrates were synthesized by slip casting method using Taguchi optimising approach. The microporous substrate was then used to coat nanoporous titania layers by the sol–gel method. The thickness, pore size, structure and permeability of the membranes were characterised using SEM, XRD, STA and Hg-Porosimetry. The process conditions to achieve defect-free nanoporous titania layers with the average pore size of about 4 nm coated on the microporous alumina substrates with the average pore size of about 270 nm were determined.
|
|
| 45. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
On the Formation of Micro-Shrinkage Porosities in Ductile Iron Cast Components
- 2018
-
Ingår i: Metals. - : MDPI. - 2075-4701. ; 8:7
-
Tidskriftsartikel (refereegranskat)abstract
- A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities.
|
|
| 46. |
- Ghassemali, Ehsan, et al.
(författare)
-
On the microstructure of micro-pins manufactured by a novel progressive microforming process
- 2013
-
Ingår i: International Journal of Material Forming. - : Springer. - 1960-6206 .- 1960-6214. ; 6:1, s. 65-74
-
Tidskriftsartikel (refereegranskat)abstract
- Microforming is defined as the process of production of metallic micro-parts with at least two dimensions in sub-millimeter range. Many of these microforming processes have been investigated in laboratory-scale, which is not suitable for industrial applications. In this work, the feasibility of producing copper micro-pins using a novel progressive microforming process is demonstrated. This process has a good potential for mass production of micro-parts. The material flow behavior and the microstructure of the formed micro-pins were investigated by means of optical microscopy and simulation. From this study of material flow behavior with respect to different process conditions (die diameter, die design and punch diameters used), it will be shown how the respective material flow behavior in the progressive forming process influenced the microstructure evolution in the formed micro-pin. It was found in the experimental results that there is a soft zone on the micro-pins surface under specific process conditions. The microhardness results were consistent with the microstructural observations. Simulation was employed to understand the material flow direction under the punch during the microforming process and evaluate the position of the neutral zone in the disk-shape head of the micro-pin produced. This understanding of the neutral zone position with relation to the metal dead-zone as well as the material flow behavior was necessary to explain the dead-zone leakage in the microstructure and the occurrence of the soft zone. By decreasing the punch to die diameter ratio, and also choosing a die without entrance fillet radius, it was shown that the soft zones at the pin surface could be either minimized or entirely removed.
|
|
| 47. |
- Ghassemali, Ehsan, et al.
(författare)
-
Optimization of axisymmetric open-die micro-forging/extrusion processes: An upper bound approach
- 2013
-
Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403 .- 1879-2162. ; 71, s. 58-67
-
Tidskriftsartikel (refereegranskat)abstract
- There is a trend towards component miniaturization and strong drive towards cost effective and sustainable metal forming techniques of miniaturized components. This paper presents an upper bound solution for the optimization of open-die forging/extrusion processes in the forming of micro-pins from a sheet metal. Using such an analytical modeling approach, the critical blank thickness, the resulting final part geometry, together with the required forming load were predicted based on the location of the neutral plane under the punch during the process. Based on the phenomenological findings of the process, the geometry size factor, x, was introduced explaining its relative importance to the model. Experimental results obtained from C11000 copper samples using a progressive microforming process was found to agree well with the results predicted by the model. The results were also validated with other results reported before from a similar process.
|
|
| 48. |
- Ghassemali, Ehsan, et al.
(författare)
-
Progressive microforming process : Towards the mass production of micro-parts using sheet metal
- 2013
-
Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer Berlin/Heidelberg. - 0268-3768 .- 1433-3015. ; 66:5-8, s. 611-621
-
Tidskriftsartikel (refereegranskat)abstract
- Although there is considerable published literature on micro-metal forming processes, there is still a lack of research towards implementing these processes commercially. Some of the challenges are handling of micro-parts and process intermittency. This work demonstrates the feasibility of producing symmetric micro-parts using a progressive forming set-up. Such a progressive forming process alleviates the challenges in handling and removal of micro-parts. Micro-pins with diameters of 0.3, 0.5, and 0.8 mm were successfully manufactured without defects. Experimental observations together with process simulation results showed that this process has three main stages: (1) indentation at the very beginning, (2) upsetting, and (3) extrusion predominantly occurring at the very end stage of the stroke. The bulk of the pin forming occurs at the end stroke of the process (extrusion stage). The effects of punch/pin diameter ratio on the pin aspect ratio and the maximum forming load were also investigated. In addition, the finite element results also revealed that a hybrid friction model was required to be implemented for better fit with experimental results as compared to the shear and Coulomb friction models.
|
|
| 49. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
-
Revisiting the graphite nodule in ductile iron
- 2019
-
Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 161, s. 66-69
-
Tidskriftsartikel (refereegranskat)abstract
- The growth mechanism of graphite nodules in ductile iron was experimentally investigated using high-resolution 3D tomography of an individual graphite nodule in a near-eutectic ductile iron. The dual beam scanning electron microscopy (FIB-SEM) technique was used for this purpose. Iron particles elongated in the radial direction were observed inside a graphite nodule. Some micro-voids were detected inside the nodule, mostly located at the end of the iron particles. These observations were compared with established theories about the growth of graphite nodules and iron entrapment/engulfment in between the graphite sectors during solidification of ductile iron.
|
|
| 50. |
- Ghatei Kalashami, A., et al.
(författare)
-
Correlation of microstructure and strain hardening behavior in the ultrafine-grained Nb-bearing dual phase steels
- 2016
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 678, s. 215-226
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrafine-grained dual phase (DP) steels with different Nb contents (0.00, 0.06 and 0.12 wt%) were produced by cold-rolling followed by intercritical annealing of ferrite/martensite starting microstructure at 770 °C for different holding times. Scanning electron microscopy, equipped with electron backscattered diffraction (EBSD) detector, nanoindentation and tensile testing were used to characterize microstructural evolutions and their correlations to the strain hardening and fracture behavior. EBSD results confirmed the retardation effect of Nb on recrystallization. It was found that the strains stored in the grains and density of geometrically necessary dislocations (GNDs) were increased with the addition of Nb. Strain hardening analysis showed that plastic deformation of the DP steels occurred in three distinct stages, which based on the EBSD results, nanoindentation and fracture analysis, were controlled by microstructural features such martensite volume fraction and size, density of GNDs and individual ferrite and martensite tensile properties.
|
|
