Development Of New High Strength And Toughness Die-cast Magnesium Alloy

As one of the lightest metal structural materials,magnesium alloy is of great significance for promoting the lightweight development of automobiles and other fields.Magnesium alloy parts are generally mass-produced by die-casting in industry.The commercially available die-cast magnesium alloys are mainly based on magnesium-aluminum systems,and the mechanical properties are relatively low,which limits the application range of die-cast magnesium alloy products.At present,researchers have developed a number of high-performance magnesium alloy materials,which are based on magnesium-rare earth alloy systems,but these high-performance magnesium alloy materials are generally prepared by gravity casting or hot working.The research on die-casting magnesium-rare earth alloys is relatively less.In this paper,the research and development of die-casting magnesium alloy,which based on magnesium-rare earth alloy system,is carried out.It is expected to develop a new high strength and toughness die casting magnesium alloy and promote the widely application of die casting magnesium alloy.In this paper,the solidification interval together with the types and contents of the second phases,within Mg-Nd-Zn,Mg-Gd-Zn and Mg-Y-Zn alloy systems,were analyzed by JMat Pro^TM material simulation software.And the microstructures and mechanical properties of alloys with typical compositions were analyzed for verification.Finally,the Mg-Y-Zn alloy system was determined to be the base system for the development of die-cast magnesium alloy.A series of（12 kinds）alloy compositions were designed based on Mg-Y-Zn alloy system.And the optimized component content was determined by the study of the microstructure and mechanical properties of gravity casting alloys in these compositions.The optimized composition of Mg-3Y-2Zn-1Al-0.3Mn was used to prepare die-cast alloy.And the die-cast microstructure and mechanical properties of the alloy were studied.The heat treatment of the die-casting alloy was also performed to study the evolutions of alloy microstructure and mechanical properties after heat treatment.The main research conclusions are:AS the content of Nd,Gd and Y within 1～5 wt.%,Zn content within0～8 wt.%,among Mg-Nd-Zn,Mg-Gd-Zn and Mg-Y-Zn alloy systems,the solidification interval of Mg-Y-Zn system is the narrowest in a wide content range.The as-cast microstructure and mechanical properties of Mg-Y-Zn system are also the optimal.It is suitable to be used as the base compostions for the development of die-cast magnesium alloy.In Mg-Y-Zn-Al-0.3Mn as-cast alloys with Y content of 3～4 wt.%,Zn content of 1～2 wt.%and Al content of 0.5～2 wt.%,the overall mechanical properties of Mg-3Y-2Zn-1Al-0.3Mn are optimal,with the yield strength of 128 MPa,tensile strength of 226 MPa,and elongation of 7.9%.A large number of fine particle phases are dispersed in the grain of Mg-3Y-2Zn-1Al-0.3Mn die-casting alloy,and the phase size is about 1μm,which has a good dispersion strengthening effect.At the same time,the phase has a good stability under high temperature.It is stable at 450°C for10 h.The room temperature tensile properties of Mg-3Y-2Zn-1Al-0.3Mn die-casting alloy are greatly improved compared with the as-cast state.It is due to the significant dispersion strengthening and fine grain strengthening effects.The tensile properties of the die-cast alloy at room temperature are yield strength of 191 MPa,tensile strength of 286 MPa,elongation of7.1%.