An Al-6.5Zn-2.3Mg-2.5Cu-0.1Zr-0.2Sc cast aluminum alloy for the lightweight requirements of key components for high-speed trains was developed.The Al-6.5Zn-2.3Mg-2.5Cu-0.1Zr-0.2Sc alloy was melted and cast,and homogenization treatment and solution and aging(T6)treatment was carried out.The tensile properties of the T6 state alloy were tested at room temperature and 200 ℃,respectively,and their microstructure characteristics were characterized by means of optical microscope,scanning electron microscope and transmission electron microscope.The results show that when aged at 120 ℃ for 10 h,the main precipitates within the grain are the GP region.As the aging time increases,GP regions transform into η'phase,and the η'phase can be clearly observed when aged for 22 h.As extending the aging time to 34 h,the η'phase gradually grows and transforms into the coarse η phase.The results of tensile tests at 200 ℃ show that the tensile strengths of the alloy aged for 22 h and 34 h are 617.7 MPa and 575.9 MPa,respectively,and the yield strengths are 600.5 MPa and 560.7 MPa,respectively,and both the fracture mechanisms are ductile fracture.
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