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  Liang, Z.; Chang, C.S.T.; Wanderka, N.; Banhart, J.; Hirsch, J.: The effect of Fe, Mn and trace elements on precipitation in Al-Mg-Si alloy. In: Proceedings of the 12th International Conference on Aluminium Alloys, September 5-9, 2010, Yokohama, JapanJapan Institute of Light Metals, 2010, p. 492-497

Abstract:
The effect of Fe, Mn and other trace elements on the ageing response of Al-Mg-Si alloy has been investigated. Three alloys were used: Al-0.4wt%-1.0wt%Si alloy with a very low level of impurities, Al-0.4wt%-1.0wt%Si with 0.25wt%Fe and 0.08%Mn and a 6016 commercial alloy containing further elements. Samples were solution heat treated and then quenched in different media. After quenching, samples were artificially aged. Their ageing responses were studied by using microhardness. Differential Scanning Calorimetry (DSC) was performed in order to investigate their precipitation behavior. Moreover, the morphology of the precipitates and intermetallic compounds were characterised by using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Result shows that, at the paint bake condition, the 6016 alloy has the largest number density of ”, and this correlates to the fact that 6016 alloy has the fastest ageing response, while the alloy containing Fe and Mn has the slowest. DSC shows that the precipitation behavior after solid solution treatment for 6016 and the alloy containing Fe and Mn is not sensitive to the cooling rates. The presence of Fe and Mn lowers the Si content in the matrix, which is necessary for the formation of ” during ageing. On the other hand, the presence of the trace elements promotes the formation of ” and increases the hardening rate during ageing despite the fact of the presence of the intermetallic compounds.