Effect of ageing on the mechanical behaviour of a novel automotive grade Al-Mg-Si alloy

The ageing behaviour of a novel Al-Mg-Si alloy AA6014 is studied against AA6111 using hardness and tensile tests. Three conditions were adopted in the tests - natural ageing (T4), artificial ageing (T6) and artificial ageing after pre-natural ageing (T4 followed by T6). The effect of ageing on edge-cracking through hole-expansion test, work hardening potential and fractography has also been studied. The ageing pattern of AA6014 is found to be similar to that of AA6111, but the effect is less severe as observed through lower values of hardness and strength at various ageing conditions. At peak aged condition, the Vickers hardness of AA6014 is 15% less than that of AA6111, whilst the ultimate tensile strength and yield strength of AA6014 are 19% and 13% lower than that of AA6111, respectively. Also, the time taken to attain peak ageing is lower in AA6014 compared to AA6111. The natural ageing prior to artificial ageing is found to have a significant effect on ageing response at shorter ageing times, whilst it is negligible at higher ageing times. The hole-expansion ratio of the two alloys are comparable at higher ageing times, whilst it is higher for AA6014 in as-quenched condition and lower ageing times. The work hardening rate of AA6014 also showed similar pattern as AA6111 and its values, lower than AA6111. The fractography supplemented the tensile test results. (C) 2012 Elsevier B.V. All rights reserved.