Effects of two-stage solution on microstructures and mechanical properties of 7A55 aluminum alloy

The effects of temperature and time of two-stage solution on mechanical properties of 7A55 aluminium alloy sheet were investigated by optical microscopy,TEM and SEM analyses and tensile testing and electrical conductivity test.The optimal two-stage solution treatment is 450℃,90min+485℃,40min.The mechanical properties σ_b,σ_(0.2) and δ reach 648.4MPa,629.6MPa and 11.9%,respectively,after aging at 120℃ for 24h.The results show that the first stage solution is crucial to the mechanical properties,and the optimal temperature is 450℃.The extensive recovery occurs after the first stage solution at 450℃,which reduces the driving force of recrystallization.Consequently,higher alloying elements supersaturation in matrix is obtained at the second stage high temperature solution and only little recrystallization happens.As a result,a better precipitation strengthening effect in subsequent aging is attained.