Microstructure And Mechanical Properties Of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe Alloys

Al-Zn-Mg-Cu aluminum alloys are widely used in aerospace,industrial and civil areas for the high strength and toughness,excellent formability and weld ability,corrosion resistance and resistance to low cycle fatigue.Digging out the potential of the alloy is still a emphasis of current studies on the aluminum alloy.Microalloying is one important means to increase the comprehensive performance of Al-Zn-Mg-Cu alloys.At present,Sc is the most effective micro-alloying element discovered to reinforced aluminum.In order to provide scientific basis for the development of a comprehensive performance of aluminum alloy.In this paper,the Al-Zn-Mg-Cu-Sc alloy adding different content of Ce elements are investigated by means of organization,aging precipitation behavior of alloy,hardness,tensile and low cycle fatigue.The results of microstructure observation show that the addition of 0.2%Ce can eliminate the dendrite of casting Al-7.5Zn-2Mg-2.3Cu-0.1Sc alloy,effectively refine as-cast,extruded and T6 treated microstructure of the alloy.The hardness and tensile test show that in the process of artificial aging in 120°C×32h,the hardness and strength of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-x Ce alloys were reduced after the increase trend.The addition of 0.2%Ce can significantly increase the brinell hardness,tensile strength and yield strength of the Al-7.5Zn-2Mg-2.3Cu-0.1Sc alloy.The observations on the fracture surfaces show that under peak aging time,the tensile fracture surface of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-0.2Ce alloys observed a large number of dimples and a small amount of the intergranular fracture characteristics,performing mainly ductile mixed fracture characteristic.The strength models of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloys are ? ' precipitates strengthening and adding 0.2%Ce can makes ? ' precipitates distribution more uniform and narrow the grain boundary precipitate free zone.The strain amplitude control of low-cyclic fatigue tests show that the T6 treated Al-7.5Zn-2Mg-2.3Cu-0.1Sc-x Ce alloys exhibit the cyclic stable cyclic stress response during fatigue deformation.Adding 0.2%Ce can improve the fatigue deformation resistance and the low cycle fatigue life of the alloy.For T6 treated Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloys,the relationship between the elastic strain amplitude and reversals to failure is linear and can be well described by the Basquin equation,while the relationship between the plastic strain amplitude and reversals to failure also exhibits a linear behavior and obeys the Coffin-Manson equation.Under the low-cycle fatigue loading condition with total strain control mode,the fatigue cracks initiate in a transgranular mode at the free surface of fatigue specimens,and propagate transgranularly for the T6 treated Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloys.