Effect of Dissolution of Precipitates on Mechanical Properties of A7075-T6 Alloy

The effects of dissolution of the eta' phase by solution treatment on the mechanical properties of A7075-T6 alloy were investigated. Immediately after solution treatment of the T6 sheet at 450 degrees C or higher, elongation significantly increased and dissolution of the eta' phase occurred. eta' is the main hardening phase. After natural-aging, GPI, which is coherent with the aluminum matrix, was formed and strength increased. When bake hardening after natural-aging was performed, the yield strength slightly increased due to partial dissolution of the GPI and re-precipitation of the eta' phase. In contrast, after solution treatment at 400 degrees C, there was less elongation increase due to the precipitation of the coarse eta phase at grain boundaries and low dissolution of the eta' phase. In addition, when bake hardening after natural-aging was performed, the yield strength decreased due to insufficient GPI, which is the nucleation site of the eta' phase. To promote reprecipitation of the eta' phase, the solution treatment temperature was set to a level that would increase solubility. As a result, the yield strength was significantly increased through re-precipitation of a large number of fine and uniform eta' phase. In addition, to increase the effect of dissolution, a pre-aging treatment was introduced and the bake hardenability can be improved after dissolution.