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 （IE） of the sheets increase greatly and reach a peak value, then decrease. Meanwhile, intermetallic com- pounds 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 ~C. Considering mechanical properties, IE value, residual phases, grain size and surface quality of the sheets, SHT temperature for the alloy should not be higher than 550 ℃.
Phase fraction and solidification path of high Zn-containing Al-Zn-Mg-Cu series aluminum alloy were calculated by calculation of phase diagram （CALPHAD） method. Microstructure and phases of Al-9.2Zn-1.7Mg-2.3Cu alloy were studied by X-ray diffraction （XRD）, differential scanning calorimetry （DSC） and scanning electron microscopy （SEM）. The calculation results show that η（MgZn2） phase is influenced by Zn and Mg. Mass fractions of η（MgZn2） in Al-xZn-1.7Mg-2.3Cu are 10.0%, 9.8% and 9.2% for x=9.6, 9.4, 8.8 （mass fraction, %）, respectively. The intervals of Mg composition were achieved for θ（Al2Cu）＋η（MgZn2）, S（Al2CuMg）＋η（MgZn2） and θ（Al2Cu）＋S（Al2CuMg）＋η（MgZn2） phase regions. Al3Zr, α（Al）, Al13Fe4, η（MgZn2）, α-AlFeSi, Al7Cu2Fe, θ（Al2Cu）, Al5Cu2MgsSi6 precipitate in sequence by no-equilibrium calculation. The SEM and XRD analyses reveal that α（Al）, η（MgZn2）, Mg（Al,Cu,Zn）2, θ（Al2Cu） and Al7Cu2Fe phases are discovered in Al-9.2Zn-1.7Mg-2.3Cu alloy. The thermodynamic calculation can be used to predict the major phases present in experiment.
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（MgZn2）. Both of as-cast 7095 and 7136 aluminum alloys involve a（Al）eutectic Al/Mg（Cu, Zn, Al）2, intermetallic g（MgZn2）, and h（Al2Cu）. During homogenization at 450 ℃, fine g（MgZn2） can dissolve into matrix absolutely. After homogenization at 450 ℃ for 24 h, Mg（Cu, Zn, Al）2 phase in 7136 alloy transforms into S（Al2Cu 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.
