The effect of solution heat treatment(SHT) on mechanical properties,microstructure and surface quality of Al-1.2Mg-0.6Si-0.2Cu-0.6Zn alloy was investigated by tensile test,Erichsen test,surface topography,scanning electron microscope(SEM) and electron back-scattered diffraction(EBSD).The results indicate that with the increase in SHT temperature,yield strength and cupping test value(I_E) of the sheets increase greatly and reach a peak value,then decrease.Meanwhile,intermetallic compounds dissolve into matrix gradually.The grains grow up as SHT temperature increases,and abnormal grain growth leads to the surface defects after solution-treated above 560 ℃.Considering mechanical properties,I_E value,residual phases,grain size and surface quality of the sheets,SHT temperature for the alloy should not be higher than 550 ℃.
Phases and microstructures of three high Zncontaining Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optica microscopy(OM), scanning electron microscopy(SEM)energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)_2 eutectic phases, and fine intermetallic compounds g(MgZn_2). Both of as-cast 7095 and 7136 aluminum alloys involve a(Al)eutectic Al/Mg(Cu, Zn, Al)_2, intermetallic g(MgZn_2), and h(Al_2Cu). During homogenization at 450 °C, fine g(MgZn_2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)_2 phase in 7136 alloy transforms into S(Al_2Cu Mg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zncontaining Al–Zn–Mg–Cu alloys.
