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Influence of Cu content on the artificial ageing response of Al-Mg-Si-Cu alloys Bao, Yinghui


There is a current trend in increased use of aluminum extrusion alloys in automotive applications. This trend is due to the increasing demand for the lightweight materials in the automotive industry. The major reason for this is government regulation of internal combustion engine powered vehicles for vehicle fuel efficiency and the corresponding reduction of emissions. The main objective of this work is to quantify the effect of Cu content on the precipitation response of Al-Mg-Si-Cu alloy during artificial ageing. In this study, four alloys with different Cu contents (0-0.9wt%) and two different initial microstructures (unrecrystallized and recrystallized) were examined. The alloys were all solution treated at 550 °C for 5 minutes and then were artificially aged at four ageing temperatures (160°C, 180°C, 200°C and 220°C). Their mechanical properties were measured by hardness and tensile tests. It was found that the addition of Cu to Al-Mg-Si alloys increases the peak yield stress. The peak yield stress increased by 60MPa and 45MPa for the recrystallized and unrecrystallized alloys, respectively, when 0.9wt% Cu was added. Based on these data, a process model for Al-Mg-Si-Cu alloys based on the Shercliff-Ashby approach was developed to model the evolution of yield strength during artificial ageing. The model contains contributions from precipitation hardening, solid solution strengthening, dislocation hardening and the intrinsic strength of the alloy. The model was verified by the good agreement between the predictions and experimental results.

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