The influence of Mg/Si ratio and Cu content on the stretch formability of 6xxx aluminium alloys

In this paper, the effect of Mg/Si ratio and Cu content on the stretch formability of aluminium alloys of the 6xxx series was investigated using scanning electron microscopy, hardness tests, tensile testing and forming limit diagram measurements. The results show that with increasing Mg/Si ratio, the formability of Al-Mg-Si alloys decreases due to a decrease in the work hardening and strain-rate hardening capability. The addition of Cu enhances the work hardening capacity, but slightly decreases the strain-rate hardening capability. In particular, it was found that the addition of 0.3 wt% Cu improves the stretch formability of alloys with Mg/Si ratios greater than one, but has little or no effect in alloys with a large excess of Si. Furthermore, the work hardening behaviour of the alloys was modelled using the Kocks-Mecking-Estrin model.