Research About Microstructures And Mechanical Properties Of Mg-10Gd-xY-(Zn)-0.6Mn Casting Magnesium Alloys

Mg-Gd-Y based rare earth magnesium alloys which are thought as promising high-performance casting magnesium alloys,have broad application prospects in aerospace,military and other fields.At present,Mg-Gd-Y based rare earth casting magnesium alloys which have received more attention,are mainly concentrated on Mg-Gd-Y-Zn and Mg-Gd-Y-Mn based alloys,thereinto a large number of studies mainly involve Mg-Gd-Y-Zn based alloys,while Mg-Gd-Y-Mn based alloys are less studied.It is well known that alloying and/or micro-alloying and heat treatment have a crucial influence on the structure and properties of Mg-Gd-Y-Mn based casting magnesium alloys.Therefore,on the basis of the existing research and development for Mg-Gd-Y-Mn based magnesium alloys,further research and develop new Mg-Gd-Y-Mn based alloys with high-performance by means of alloying and/or micro-alloying and heat treatment strengthening,has important theoretical significance and practical reference value for promoting the application of Mg-Gd-Y-Mn based casting magnesium alloys.Based on the research results of the existing Mg-Gd-Y-Mn based rare-earth magnesium alloys,the new Mg-Gd-Y-Mn based rare-earth magnesium alloys were prepared by changing Y content and adding Zn element.Furthermore,by optical microscope(OM),electron microscope(SEM),X-ray diffractometer(XRD),energy spectrum analyzer(EDS),differential thermal analysis(DSC),tensile properties and micro-hardness testing and other methods,the effects of the change in alloy compositions and heat treatment process on the microstructures and mechanical properties of the experimental magnesium alloys were investigated,and the following main research conclusions were obtained:1)The as-cast microstructures of the Mg-10Gd-x Y-0.6Mn(x=1-3wt.%)experimental magnesium alloys exhibit the typical dendritic structure,which is mainly composed of the?-Mg matrix and the skeletal Mg₂₄(Y,Gd)₅and block Mg₅(Gd,Y)phases with large amount,which indicates that the change of Y content has no obvious effect on the type of alloying phase.However,as Y content increases from 1 wt.%to 3 wt.%,the amount of the second phases in the experimental alloys increases,and the size of the second phase and grains first decrease and then increase.Correspondingly,the tensile properties at room temperature for the experimental alloys first increase and then decrease.The experimental alloy containing 2 wt.%Y shows the relatively high as-cast tensile properties.2)Heat treatment has a significant effect on the microstructure and tensile properties of the Mg-10Gd-x Y-0.6Mn(x=1-3wt.%)experimental magnesium alloys.After being solid-solution treated at 460-520?for 4-24h,the type of the second phases in the alloys does not change significantly,but their quantity and size reduce.At the same time,after being aged at 520?×24h+200-250?×24h,the dispersed second phases in the alloys are precipitated in the grain boundaries and grains.In addition,after the experimental alloys are solid-solution treated at 520?×12h,the tensile properties of the alloys show a decreasing trend,while after being solid-solution treated at 520?×24h,the tensile properties of the alloys increase slightly.Furthermore,after being treated by solid solution at 520?×24h and aging at 200?/225?×24h,the overall tensile properties of the alloys are further improved,especially the most obvious improvement is observed for the alloy aged at 225?×24h.Among the experimental alloys with different Y content,the aged tensile performance of the alloy with 2 wt.%Y are relatively better,and its tensile strength,yield strength and elongation reach 228.4MPa,186.5MPa and 7.4%,respectively.3)The as-cast microstructures of the Mg-10Gd-x Y-1.0Zn-0.6Mn(x=1-3 wt.%)experimental magnesium alloys exhibit the typical dendritic structure,which is mainly composed of?-Mg matrix and the Mg₅(Gd,Y),Mg₂₄(Y,Gd)₅and Mg₁₂Zn(Y,Gd)eutectic phases,indicating that the change of Y content has no obvious effect on the type of alloying phase.However,as the Y content increases from 1 wt.%to 3 wt.%,the change in Y content causes the number of the second phases in the alloys to increase,and the size of the second phases and grains first decrease and then increase.Correspondingly,the tensile properties at room temperature for the experimental alloys first increase and then decrease.The experimental alloys containing 2 wt.%Y shows relatively high as-cast tensile properties.4)Heat treatment has a significant effect on the microstructure and tensile properties of the Mg-10Gd-x Y-1Zn-0.6Mn(x=1-3wt.%)experimental magnesium alloys.After being solid-solution treated at 460-520?×4-24h,the number and size of the second phase in the alloys are significantly reduced,and the higher is the solution temperature,the less is the number of the second phases.At the same time,after being aged at520?×24h+200-250?×24h,the size of the grain in the alloys becomes smaller and the dispersed second phases are precipitated.In addition,after being solid-solution treated at520?×12h/24h,the tensile properties at room temperature for the alloys show an overall increasing trend,thereinto the improvement under the conditions of the solid solution at520?×24h is better than that of under the conditions of the solid solution at 520?×12h.However,after being aged at 520?×24h+200?/225?×24h,although the elongation of the alloy is obviously increased,the tensile and yield strengthes are not improved.Among the experimental alloys with different Y contents,the aged tensile properties of the alloy with 2 wt.%Y are relatively high,and its tensile strength,yield strength and elongation reach 212.7MPa,189.6MPa and 9.8%,respectively.5)For the Mg-10Gd-x Y-0.6Mn(x=1-3 wt.%)and the Mg-10Gd-x Y-1Zn-0.6Mn(x=1-3 wt.%)experimental magnesium alloys,the change of Y content has the obvious effects on the as-cast and heat-treated tensile properties of the alloys.Among the alloys with four Y contents of 1,1.5,2 and 3 wt.%,the alloy with 2 wt.%Y shows the relatively high as-cast and heat-treated tensile properties.