Solution strengthening and age hardening capability of Al–Mg–Mn alloys with small additions of Cu

Abstract

Nine Al–(1–3)Mg–(0–0.4)Cu–0.15Si–0.25Mn (in wt.%) alloys with potential applications in both packaging and automotive industries have been investigated. Tensile testing showed that solution strengthening is in good approximation linearly proportional to the Mg content. Mechanical testing and microstructural examinations of aged samples indicate that Mg 2Si phase precipitates contribute to age hardening of Cu-free alloys, whilst both Mg 2Si phase and S (Al 2CuMg) phases contribute to that of Cu-containing alloys. The age hardening capability is critically influenced by solution treatment temperature: increasing the solution treatment temperature from 500 to 550 °C results in a marked increase in rate of hardening for Cu-containing alloys and solution treatment at about 550 °C or higher is needed to allow Mg 2Si phase precipitation during ageing in Cu-free alloys with Mg content of about 2% or higher.