Influences of homogenization temperature and Cu addition on age-hardening behavior of Al–Mg–Si alloys

Abstract

Influences of homogenization process and Cu addition on age-hardening behavior of an Al–0.93%Mg2Si alloy were investigated. According to variation in electrical resistivity converted from the IACS%, Mg and Si solute concentration was decreased by the ingot homogenization at 723 K for 7.2 ks. The resistivity of a 0.5%Cu added alloy was higher than that of the base alloy and their difference was maintained almost constant for three homogenization temperatures, 723 K, 773 K and 823 K. Therefore, it is considered that almost all of the added 0.5%Cu was dissolved in matrix solid solution at all temperatures of the homogenization. The size and number density of secondary phase particles of intermetallic compounds obtained by SEM image analysis elucidated that volume fraction of Mg–Si particles was increased by the homogenization at 723 K, though no change was observed in that of Al–Fe–Si particles. After the homogenization treatment, ingots were rolled to 1.0 mm thickness. Tensile specimens sampled from the rolled sheets were held at 803 K for 15 s and quenched into water. Yield strength of 723 K homogenized specimens after T4, natural aging for more than one week, and final artificial aging at 443 K or 473 K was lower than that of specimens homogenized at 773 K or 823 K. To ensure enough high age-hardenability in the present alloys, it is necessary to homogenize ingots at temperature above 758 K, the complete dissolving temperature of Mg and Si. The Cu addition up to 0.7% increased yield strength after the artificial aging in all homogenizing and aging conditions.