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| 2. |
- Wei, L.Y., et al.
(författare)
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Age hardening and precipitation in a cast magnesium-rare-earth alloy
- 1996
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 31:2, s. 387-397
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Tidskriftsartikel (refereegranskat)abstract
- The precipitation sequence responsible for the age-hardening behaviour of a cast Mg-1.3 wt% rare-earth alloy has been investigated by analytical electron microscopy. Very fine intermediate precipitates formed at an early stage of ageing. Plate-shaped Mg3MM β precipitates (MM = misch metal) and hexagonal prism-shaped Mg12MM β precipitates were primarily responsible for age hardening. Precipitate morphologies, crystal structures and crystallographic orientation relationship were determined for the various types of precipitates that formed during ageing at different temperatures.
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| 3. |
- Wei, L.Y., et al.
(författare)
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Crystal symmetry of the pseudo-ternary T-phases in Mg-Zn-rare earth alloys
- 1996
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Ingår i: Journal of materials science letters. - 0261-8028 .- 1573-4811. ; 15:1, s. 4-7
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Tidskriftsartikel (refereegranskat)abstract
- Crystal symmetry of the pseudo-ternary T-phases in Mg-Zn-rare earth alloys was observed. The convergent beam electron diffraction combined with selected area electron diffraction (SAED) determined the point group and space group for this phase. The phase was formed interdendritically during the solidification of the alloys. Extensive SAED detected a C-centered orthorhombic crystal structure of the phase. The space group for T-phase is Cmcm
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| 4. |
- Wei, L.Y., et al.
(författare)
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Development of microstructure in cast Mg-Al-rare earth alloys
- 1996
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 12:9, s. 741-750
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Tidskriftsartikel (refereegranskat)abstract
- The microstructures and age hardening behaviors of a series of Mg-Al-rare earth (RE) alloys that had been either pressure die cast or permanent mold cast were investigated by SEM and analytical TEM. Two types of phases, Al sub 4 MM and Al sub 12 Mg sub 17 , were found in the as cast alloys and no pseudoternary Mg-Al-RE phases were present. The Al sub 4 MM phase was thermally stable during solution treatment at temperatures as high as 500 deg C, whereas Al sub 12 Mg sub 17 partially dissolved in the alpha -Mg matrix during solution treatment at 420 deg C. No rare earth containing precipitates formed during heat treatment of the investigated alloys but two types of Al sub 12 Mg sub 17 precipitation took place. Colonies of discontinuous precipitation containing alternate lamellae of alpha -Mg and Al sub 12 Mg sub 17 formed preferentially in regions of alpha -Mg with high Al content. Spheroidization and coarsening of the discontinuous precipitates occured after aging at 200 deg C. Continuous precipitation of Al sub 12 Mg sub 17 also occurred and these precipitates had a rodlike morphology and grew in preferred crystallographic directions
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| 5. |
- Wei, L.Y., et al.
(författare)
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Intergranular microstructure of cast Mg-Zn and Mg-Zn-rare earth alloys
- 1995
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 26A:8, s. 1947-1955
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Tidskriftsartikel (refereegranskat)abstract
- The solidification path and microstructure of cast Mg-9Zn and Mg-8Zn-1.5 MM (misch metal) alloys have been investigated by a combination of thermal analysis and analytical electron microscopy. The addition of 1.5 wt pct MM had a strong influence on the as-cast microstructure with the introduction of new `ternary' interdendritic phases and structural modification of known binary phases. The temperature ranges for formation of these phases from the melt were identified, their crystal structures determined, and their compositions analyzed. Products from eutectoidal decomposition of the interdendritic phase in the binary Mg-9Zn alloy were also identified
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| 6. |
- Wei, L.Y., et al.
(författare)
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Precipitation hardening of Mg-Zn and Mg-Zn-RE alloys
- 1995
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 26A:7, s. 1705-1716
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Tidskriftsartikel (refereegranskat)abstract
- The age-hardening response of two cast Mg-Zn-RE alloys has been investigated and compared with that of a binary Mg-Zn alloy. The microstructures of the aged specimens were examined by analytical electron microscopy. Formation of a fine dispersion of rodlike β prime 1 precipitates is the main cause for age hardening, while extensive precipitation of disc-shaped β prime 2 coincides with the onset of overaging. Rare earth additions retard the formation of β prime 2 precipitates and thus postpone overaging. Four different orientation relationships between β prime 2 precipitates and matrix were found and explained in terms of the near-CSL model.
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| 7. |
- Wei, L.Y., et al.
(författare)
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Solidification behaviour of Mg-Al-rare earth alloys
- 1996
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 232:1-2, s. 264-268
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Tidskriftsartikel (refereegranskat)abstract
- Solidification paths and as-cast microstructures were determined for the Mg-Al-MM (misch metal) alloys: AE21, AE41 and AE91. Two types of interdendritic phase were identified using analytical electron microscopy. These were Al4MM and Al12Mg17. Only Al4MM was found in AE21 while both phases were found in the other two alloys. Most of the solidification in AE21 takes place in a rather narrow solidification gap (approx.40°C), while this gap is much greater (approx. 150°C) in the higher Al alloys. This combined with the large volume fraction of interdendritic eutectic phases explains the good castability of AE91
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| 8. |
- Wei, L.-Y., et al.
(författare)
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The role of TEM in the development of materials in the automotive industry
- 1997
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Ingår i: 30th International Symposium on Automotive Technology and Automation, Florence, Italy, 16th - 19th June 1997. - : Automotive automation. - 0947719946 ; , s. 349-356
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Konferensbidrag (refereegranskat)abstract
- The aim of the present article is to highlight two examples of the unique role that transmission electron microscopy (TEM) can play to solve complex materials problems. The strength and fatigue resistance of cast Al alloys can be increased by adding copper and magnesium. TEM work revealed that a cylinder head alloy (Al-8Si-3Cu-0.3Mg) was effectively age-hardened by the formation of finely dispersed precipitates of ϑ" (CuAl2) and β" (Mg2Si) phases. The two precipitates were distinguished by the TEM. The geometry, the orientation, the shape and the size, etc., of the precipitates were completely characterized. A new type of precipitate containing Mn, Si, Cu and Al and finely dispersed in the matrix was discovered in this work. The second example is a TEM/STEM study of a grey iron. Alloying additions of, for example, Mo and Cu in the grey iron have a considerable effect in the strengthening of the alloy. It was found that Mo toughened the ferrite/Fe3C interface by forming a multi-layer structure on the surface of the cementite, and the ferrite matrix was strengthened by solution of Cu in the solid state and by a fine dispersion of coherent precipitates
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