Effects of various pre-treatments and cold rolling on room temperature aging of 6000 series aluminum alloys

Abstract

Three commercial age-hardenable alloys, 6022, 6063, 6N01, were cold rolled: CR at room temperature after the three different pre-treatments, which are solution treatment and iced water quenching: STQ, aging at room temperature for 864 ks after the STQ: RTA-1 and furnace cooling after holding at 623 K for 3.6 ks: O. These specimens were aged at room temperature for longer than 864 ks after the CR (RTA-2). Change in resistivity ρ at 77 K was traced from immediately after the CR to investigate work hardening and aging behavior at room temperature after CR. Vickers hardness HV was also measured 0.6 to 0.9 ks later from the STQ or CR. Increments in ρ and HV by the CR in the O state were smallest among the other pre-treatments. The CR in the STQ or RTA-1 state gave nearly same increments in ρ and HV. By the CR in the STQ state, aging rate of the RTA-2 was decreased with increasing true rolling strain. It is considered that this suppression of the RTA-2 may be attributed to “sweep out” of excess quenched-in vacancies by moving dislocations. This effect is expected to decrease the negative effect of room temperature aging on artificial age-hardening through decrease in amount of formed clusters by T3 treatments. In the final room temperature aging, RTA-2, after the RTA-1 and CR, initial aging rate was increased with true rolling strain. This observation suggests that vacancies were surely introduced by the CR. However, the acceleration of the RTA-2 was limited only short period till the excess vacancies annihilated to dislocations, which density was increased by the CR.