The Effect of Pre-Ageing and Addition of Copper on the Precipitation Behaviour in Al-Mg-Si Alloys

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Hardness measurements and 3-dimensional atom probe analysis have been used to characterise the precipitation behaviour in two 6xxx series aluminium alloys, one Cu-free alloy (Al-0.78at%Mg- 0.68at%Si) and one Cu-containing alloy (Al-0.78at%Mg-0.68at%Si-0.30at%Cu). The heat treatments consisted of either natural ageing or pre-ageing at 353K followed by a paint-bake treatment at 453K. Natural ageing was seen to increase the hardness, and hence reduce formability compared to pre-ageing. In addition, the strengthening effect of artificial ageing was less after natural ageing than after pre-ageing. In the Cu-free alloy, needle-like β″ was observed to form only after a pre-ageing treatment during the first 60 minutes of a paint-bake treatment. In the Cucontaining alloy, needle-like β″ formed during paint bake in both the naturally-aged and pre-aged material, although it is formed more rapidly after pre-ageing. This was accompanied by an increase in strength over the Cu-free alloy and indicates that Cu reduces the deleterious effect of natural ageing.

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Periodical:

Materials Science Forum (Volumes 519-521)

Edited by:

W.J. Poole, M.A. Wells and D.J. Lloyd

Pages:

543-548

DOI:

10.4028/www.scientific.net/MSF.519-521.543

Citation:

A.I. Morley et al., "The Effect of Pre-Ageing and Addition of Copper on the Precipitation Behaviour in Al-Mg-Si Alloys", Materials Science Forum, Vols. 519-521, pp. 543-548, 2006

Online since:

July 2006

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$35.00

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