Abstract
Effects of solution treatment temperature, TST, and Cu addition on aging behavior of 6063 alloy at 448 K and room temperature were investigated through changes in resistivity ρ and hardness HV. Calculated complete dissolution temperature of Mg and Si, TCD, was about 760 K for present alloys. Above 773 K, ρSTQ, the ρ immediately after the solution treatment and water quenching, increased slightly. Most of the increment could be explained by increase in equilibrium solute Fe concentration. Therefore, it is concluded that increase in quenched-in vacancy concentration with the TST will be small. Solution treatment at 748 K, below the TCD, lowered maximum hardening by the aging at 448 K, also maximum resistivity increment in initial stage of aging at 448 K and the ρ increment by aging at room temperature until 3Ms. Maximum age-hardening at 448 K slightly increased with TST above 773 K. However, hardening by 448 K-1.2 ks aging, simulating bake-hardening, showed small dependence on TST above 773 K. Resistivity increment by aging at room temperature for 3 Ms decreased largely by solution treatment at 748 K. Because elevation of the TST beyond 773 K gave only small effect on the resistivity increment by aging at room temperature, rate of cluster formation will be suppressed more largely by solute concentration than excess vacancy concentration.
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