Effect Of Sc On Low-cycle Fatigue Property Of Extruded Al-4Cu-1Nd Alloy

In order to provide the theoretical basis for the engineering application of aluminum alloy,the effect of rare earth Sc and aging time on both microstructure and mechanical properties of Al-4Cu-1Nd alloy has been investigated through performing the hardness test,tensile test,low-cycle fatigue test,metallographic analysis,X-ray diffraction analysis,scanning electron microscope observation and transmission electron microscope observation.The results of microstructural observation show that for as-cast Al-4Cu-1Nd alloy,the addition of 0.1% rare-earth element Sc can effectively refine the grains of ?-Al matrix.With continuously adding the rare-earth element Sc to 0.2%,the grain size of alloy has no significant change compared with the grain size of Al-4Cu-1Nd-0.1Sc alloy.The rare-earth element Sc can effectively prohibit the grain growth during the solid-solution treatment of extruded Al-4Cu-1Nd alloy with T6 treated state and promote the homogeneous precipitation of second phases.The results of hardness and tensile tests show that with the increase of aging time,the Brinell hardness,ultimate tensile strength and yield strength of extruded Al-4Cu-1Nd-xSc alloys with T6 treated state firstly increase and then decrease while the elongation significantly decreases.The Al-4Cu-1Nd alloy reaches the peak aging state when aged for 18 h,the Al-4Cu-1Nd-0.1Sc alloy reaches the peak aging state when aged for 12 h,and the Al-4Cu-1Nd-0.2Sc alloy reaches the peak aging state when aged for 10 h.At the same aging time,the strength of Al-4Cu-1Nd-0.2Sc alloy is the highest wihle the elongation of Al-4Cu-1Nd-0.1Sc alloy is the highest.The results of low-cycle fatigue test show that the cyclic stress response of extruded Al-4Cu-1Nd-xSc alloys with T6 treated state exhibit the cyclic hardening and cycle stability under the low cycle fatigue loading condition.The addition of rare earth element Sc can improve the cyclic deformation resistance of Al-4Cu-1Nd alloy.The addition of 0.1%Sc to Al-4Cu-1Nd alloy significantly enhance its low-cycle fatigue life.However,the low-cycle fatigue life of Al-4Cu-1Nd-0.2Sc alloy has remarkably reduced with adding rare earth element Sc to 0.2%.The plastic and elastic strain amplitudes of extruded Al-4Cu-1Nd-xSc alloys with T6 treated state as a function of reversals to failure show a linear relationship and obeys the Coffin-Manson equation and Basquin equation,respectively.The observation results on the fatigue fracture surfaces reveal that the fatigue cracks for the extruded Al-4Cu-1Nd-xSc alloys with T6 treated state initiate in a transgranular mode on the surface of fatigue specimen and growth in a transgranular mode.