Effects of Cu Content and Preaging on Precipitation Characteristics in Aluminum Alloy 6022

Effects of Cu content and preaging treatments on precipitation sequence and artificial aging response in aluminum alloy 6022 were investigated using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and hardness tests. It was found that Cu induces the formation of Q and its precursor metastable phases and has a beneficial effect on the kinetics of artificial aging. For the alloy with 0.07 wt pct Cu, the precipitation sequence is GP zones → needlelike b 9 → rodlike b 8 1 lathlike Q8 → b 1 Si. On the other hand, the precipitation sequence in the alloy with 0.91 wt pct Cu is GP zones → needlelike b 9 → lathlike Q8 → Q 1 Si. For the artificial aging condition of 20 minutes at 175 8C, which is the typical automotive paint bake condition, suitable preaging treatments were found to significantly reduce the detrimental effect of the natural aging on artificial aging response.