Microstructure And Mechanical Properties Of High-Performance Of Extruded Mg-Al-Ni Alloys

Extruded magnesium alloys have much greater application and development potential, compared with those cast magnesium alloys.Through solid forming,such magnesium alloy products as plate,rod,pipe and forging with various size can be manufactured.In addition,by controlling the microstructure of magnesium alloys and performing heat treatment,extruded magnesium alloys can achieve the higher strength,better ductility and multiplex mechanical properties in order to meet the need of more components and extend application fields of magnesium alloys.Obviously,to develop new high-performance of extruded magnesium alloys have become the hot point in present research field of magnesium alloys.Through melting,casting and hot extrusion,the Mg-xAl-3%Ni alloys with different Al contents have been fabricated.Subsequently,the extruded Mg-xAl-3%Ni alloy are subjected to solid solution plus aging.The effect of heat treatment on the microstructure, mechanical properties and fracture behavior of the extruded Mg-xAl-3%Ni alloys has been investigated.The microstructure observations reveal that the grains of extruded Mg-xAl-3%Ni alloys become coarse after solid solution plus aging treatment,compared with those of as-extruded alloys.The results of tensile experiments at room temperature,150℃and 200℃show that solid solution plus aging treatment can increase elongation of the extruded Mg-xAl-3%Ni alloy at room temperature,but decrease elongation of the extruded Mg-xAl-3%Ni alloys at high temperature as well as ultimate tensile strength and yield strength of the alloys at various temperatures.With increasing temperature,the ultimate tensile strength and yield strength of the extruded Mg-xAl-3%Ni alloys decrease,while the elongation of the alloys increases.The results of low-cyclic fatigue tests show that the extruded Mg-xAl-3%Ni alloys exhibit the cyclic strain hardening during fatigue deformation.For the extruded Mg-xAl-3%Ni alloys,the relation between plastic and elastic strain amplitudes as well as reversals to failure can be described by Coffin-Manson and Basquin equations,respectively. Among the four extruded Mg-5%Al-3%Ni alloy,the fatigue lives of the extruded Mg-5%Al-3%Ni alloy are the highest.The fractographic analysis reveal that under tensile loading conditions,as-extruded Mg-xAl-3%Ni alloys show typical ductile fracture.The extruded Mg-xAl-3%Ni alloys subjected to solid solution plus aging treatment show the mixed ductile and brittle fracture. Under low-cycle fatigue loading conditions,the cracks initiate transgranularly at the surface of the fatigue samples and propagate in a transgranular mode.