On the dissolution rates and mechanisms of Al-Mg and Al-Cu alloys during acid pickling using element-resolved electrochemistry

• Acid pickling is a one-step process prior to the conversion coating of aluminum alloys, an alternative to the two-step degreasing-deoxidizing. Selective dissolution may lead to enrichment or depletion of alloying elements with important consequences for corrosion resistance. In this work, the mechanisms of selective dissolution were explored using element-resolved electrochemistry for Al-3at.%Cu and Al-3at.%Mg, representing two extremes of the galvanic series. Pickling reactions were investigated in sulfuric and nitric acids with and without Fe(III) additives. The microstructure of the Al-3at.%Cu alloy was varied by heat treatment. Al-3at.%Mg showed congruent dissolution throughout the steady state in all electrolytes while Al-3at.%Cu underwent selective dissolution with surface enrichment of Cu and a significant release of detached Cu-rich particles in sulfuric acid. With the presence of Fe(III) in the electrolyte, Cu dissolved congruently, and the dissolution kinetics of these two alloys were also markedly enhanced. Experimental Evans diagrams were determined to clarify the electrochemical nature of the reactions. © 2023 The Author(s)

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Al-Cu alloy

Al-Mg alloy

Dissolution mechanism

Pickling

Spectroelectrochemistry

Additives

Alloying elements

Aluminum coatings

Aluminum corrosion

Binary alloys

Copper alloys

Corrosion resistance

Corrosion resistant coatings

Dissolution

Electrolytes

Iron compounds

Magnesium alloys

Acid pickling

Congruent dissolutions

Conversion coatings

Cu alloy

De-greasing

Dissolution rates

One-step process

Selective dissolution

Steady state

Aluminum alloys

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