Effects of the quenching water temperature and cryogenic treatment on the subsequent aged microstructure and mechanical properties of Al-Zn-Mg-Cu alloy were investigated.The results show that the addition of cryogenic treatment before aging has little effect on the strength of the Al-Zn-Mg-Cu alloy,but it can enhance the elongation after fracture.Different water temperatures for quenching affects the mechanical properties of the Al-Zn-Mg-Cu alloy,of which the best mechanical properties after the solution treatment and aging can be achieved by room temperature water quenching,as the tensile strength is 720 MPa,the elongation after fracture is 7.70％and the fracture toughness is 32.37 MPa·m12.Moreover,after the solution treatment+cryogenic treatment+aging,the elongation after fracture increases to 8.90％and the fracture toughness increases to 36.61 MPa·m1/2.The addition of cryogenic treatment does not change the precipitated phase type of the alloy,which is still η'phase,but it can increase the number of η'phase and make its distribution more uniform and dispersed,and increase the inter-spacing of precipitated phase at the grain boundary and make it distributed discontinuously.The cryogenic treatment can stabilize the fracture toughness of the alloy and reduce the effect of temperature difference of the quenching medium on the mechanical properties of the alloy.
Al-Zn-Mg-Cu alloyultra-high strength aluminum alloyquenching water temperaturecryogenic treatmentstress relief
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