The Study Of Thermal Stability Of Al-Zn-Mg-Cu Alloys

Al-Zn-Mg-Cu alloy was widely used in aerospace,military and other fields because of their excellent comprehensive properties.In order to further improve its performance and extend its application scope,the Zr,Sc and Er were firstly added into the Al-Zn-Mg-Cu alloy,and the suitable addition of the three elements was studied.On the basis,the thermal stability of the Al-7.0Zn-2.5Mg-0.25Cu-0.2Zr-0.1Sc and the Al-7.0Zn-2.5Mg-0.25Cu-0.2Zr-0.067Sc-0.033Er alloys were discussed.The effect of the hot working process?homogenization,hot extrusion,solid solution and aging?and holding temperature?heat preservation at 190?,220?,250?,280?and 310?for 4h?and holding time?heat preservation at 220?for 1h,2h,4h,8h and 16h?for the microstructure of alloys was observed by optical microscope,scanning electron microscope to study of microstructure evolution of the alloy in different periods.The mechanical properties of the alloy after thermal insulation process were measured by mechanical tensile testing machine,the fracture morphology was observed,and the thermal stability of the alloys with different components was evaluated.Several conclusions can be summarized as follows:?1?The Al-Zn-Mg-Cu alloys were alloyed with different contents of Zr,Sc and Er,the microstructure of as-cast ally was obviously refined,and the tensile properties of the alloys were greatly improved.And the comprehensive properties the alloy with the addition of0.2wt.%Zr and 0.1wt.%Sc or with the addition of 0.2wt.%Zr,0.067wt.%Sc and0.033wt.%Er were excellent.?2?The S phase?Al₂CuMg?was formed at the grain boundary after homogenization treatment at 470 for 12h in the Al-7.0Zn-2.5Mg-0.25Cu-0.2Zr-0.1Sc alloy.And the Al₃?Sc,Zr?particles were found in the alloy after solid solution and aging.In addition,obvious recrystallization phenomenon was observed in the alloy with different components after hot extrusion.?3?The tensile strength of Al-7.0Zn-2.5Mg-0.25Cu-0.2Zr-0.1Sc alloy is 389MPa after held at 220?for 8h,which is 28.9%lower than that of alloy without heat preservation.The tensile strength of Al-7.0Zn-2.5Mg-0.25Cu-0.2Zr-0.067Sc-0.033Er alloy is 369MPa after held at 220?for 8h,which is 29.4%lower than that of alloy without heat preservation.And the tensile strength of the two alloys decreased below 70%after held for 4h at 250?,280?and 310?.