Ａｌ‐１％Ｍｇ２Ｓｉ合金の４７３Ｋ時効挙動に及ぼす銅添加の影響の比抵抗法による検討

Abstract

Al–1%Mg2Si–0, −0.17, −0.43, −0.72%Cu alloys were solution treated for 3.6 ks at 848 K, water quenched and aged at 473 K. Behavior of added Cu during these heat treatments and effect of the Cu on age-hardening were investigated by resistometry and tensile test with assist of transmission electron microscopy. The resistivity in as water quenched state well coincides with the value calculated from 0.023 mass%Fe, the equilibrium solubility at 848 K in Al–Fe binary system, and all of other elements in solution. Moreover, the resistivity increases linearly with amount of the added Cu. Namely all of the added Cu is dissolved in the as quenched state. By Cu addition, the initial age-hardening rate at 473 K aging is increased and the softening with over-aging is suppressed. Though the Cu addition increases proof stress at peak age-hardening, it also decreases the resistivity decrement from the as quenched state caused by the aging. This discrepancy, that the small total amount of precipitates, which is suggested from small decrement of resistivity by the peak aging, gives the larger age-hardening, can be explained by the decrease in average length with Cu addition which may be directly related to the increase in number of needle shaped precipitates per unit area.