Effects of heat treatment on the microstructure of as-deposited ultrahigh strength aluminium alloys

Billets of Al-12Zn-2.4Mg-1.1Cu-0.20Zr-0.30Sc-0.30Ni alloys were fabricated by spray deposition (the Osprey process),and the effects of heat treatment at different temperatures on the microstructural evolution were investigated by DSC,XRD,SEM,and TEM.The results show that many η-phase particles disperse in the as-deposited alloy base at room temperature.The re-dissolution and precipitation effect of solute elements occurred at different heating temperatures can affect the microstructure and mechanical properties of the alloys.The metastable T phase ((Al,Zn)₄₉Mg₃₂) forms around η-phase particles with a high Cu content after a heat treatment at 460℃ for 8h,and disappears at 490℃ for 8h.Al₃(Sc,Zr) dispersoids are precipitated at 490℃/8h,the highest hardness (192 HV) of the as-deposited alloys after treatment at 490℃/8h is attributed to the precipitation hardening of Al₃(Sc,Zr) dispersoids and the solution hardening effect caused by Cu.