Influences Of Element Gd And Hot Extrusion On Microstructure And Mechanical Properties Of AM50 Alloy

By means of hot extrusion and measurement of the mechanical properties,the influences of the trace Gd and hot extrusion treatment on microstructure and mechanical properties of AM50 alloy are investigated by microstructure observation OM,SEM and TEM.Results show that,after alloyed by trace element Gd,the microstructure of AM50 alloy consists ofα-Mg matrix,Mg₁₇Al₁₂ and Mg₂Gd phases,thereinto,the Mg₂Gd particles phase with high melting point are dispersedly distributed in the matrix of the alloy.By the alloying treatment of the element Gd,the ultimate tensile strength(UTS) and the yield strength of AM50 alloy are obviously improved,the extent of the alloy strength enhanced increases with the measuring temperatures.The yield strength of the alloy is decreased,and the plasticity of the alloy is improved after solution treatment.After hot extruded,the grains size of AM50 and AM50-1%Gd alloys are fined,which enhances the ultimate tensile strength(UTS) and the yield strength.As the extruded temperature decrease,the grains size of the alloy is reduced,and the strength value of the alloy increase to a great extent.In the period of the aging,the finer Mg₁₇Al₁₂ phase is precipitated along the grain boundary of the extruded alloy.This improves again the ultimate tensile strength and the yield strength of the alloy at RT and high temperature,the values of UTS and YTS are enhanced to 316.5 MPa and 233.9 MPa,respectively.,compared with as-casting state, the extent of the strength values increased is up to 83%and 155.2%,respectively.The finer grains in the extruded state alloy results from the dynamic recrystallization occurred during hot extrusion.The reason of enhancing the ultimate tensile strength of the alloy is attributed to the deformation strengthening and grain size fined occurred during hot extrusion.And the main reason that a better synthesis mechanical properties is displayed in the aged alloy results from the effect of the deformation strengthening,the grain refinement and the secondary strengthening.The deformation mechanism of the extruded state alloy during tensioned up to fracture is considered to be dislocation slipping and twinning.The density of the dislocation decreases with the increase of tensioned temperature,so as to weaken the effect of the deformed strengthening,which is a main reason of decreasing high temperature strength of the alloy.