銅を添加したAl-Mg-Si合金のベークハード性に及ぼす自然時効と高温予備時効の影響

The effects of natural aging at 20°C and pre-aging at 100°C on the bake hardenability of Cu added Al–Mg–Si alloys have been studied by tension testing, hardness measurements, electrical resistance measurements and a differential scanning calorimetric analysis (DSC). The bake hardenability of the base alloy (0%Cu) was enhanced by the Cu addition. Moreover, the decline in the bake hardenability during natural aging slowly decreased with the Cu content. Because the increase in the forming cluster (1) was restrained by the Cu addition during the brief natural aging, the β″ phase then immediately precipitated during baking at 170°C for 1.2 ks. Pre-aging at 100°C after quenching significantly affected the bake hardenability of the Cu added alloys. The increase in the forming cluster (1) was also restrained by pre-aging during the natural aging. Therefore, the pre-aged Cu added alloys have a superior bake hardenability compared to the 0%Cu alloy after natural aging.