Effect Of Substitutional Atom On Microstructure And Deformation Behavior Of Mg-Zr Alloys

For the good comprehensive mechanical properties,magnesium alloys are praised as the most development perspective green structural materials in the 21 st century and have been extensively used in the areas of aerospace,automobile,the 3C electronics,etc.Nevertheless,the poor mechanical properties,such as root-temperature strength,plasticity and high-temperature creep resistance,of casting magnesium alloy limit their further industrial application.Therefore,it is very important to improve the room and high temperature strength of magnesium alloy.In this paper,effects of alloy elements,like Mn,Ag,Ca and Nd,on the annealing strengthening of Mg-0.3Zr alloys are firstly investigated by means of in-situ metallographic analysis,Transmission Electron Microscope,compression test and multi-directional deformation method.Secondly,influence of Nd and Zr contents on the microstructure and deformation behavior of Mg-Nd-Zr alloys are studied.Finally,the conclusions can be drawn as follows:The optimal solution treatment process of Mg-8.3Ag-0.3Zr,Mg-1Ca-0.3Zr and Mg-5.3Nd-0.3Zr alloy are 450?×8h,510?×8h,550?×9h,respectively.The main second phases in as-cast Mg-8.3Ag-0.3Zr,Mg-1Ca-0.3Zr and Mg-5.3Nd-0.3Zr,in turn,are AgMg3,Mg2 Ca and Mg12 Nd,respectively.There are no annealing strengthening effects of Mn and Ag elements on pre-deformed Mg-0.3Zr magnesium alloy.The additions of Ca and Nd elements can markably improve the compression strength of pre-deformed Mg-0.3Zr alloys and the optimal annealing process is 150?×24h with increment of 40 MPa and 180?×7h with increment of 76 MPa,respectively.Moreover,the compression strength increases with increasing of Nd content and excess Nd addition does not reinforce the annealing strengthening effect on pre-deformed Mg-0.3Zr alloy.During annealing process,Nd will segregate in the twin boundary of Mg-Nd-0.3Zr formed in the pre-compression test to hinder the broadening of the twin boundary.So the formation of new twins rather than the growth of the pre-deformed twins is the main deformation mechanism of Mg-Nd-0.3Zr alloy in the subsequent compression course,which results in the increase of the compression strength.The strength of Mg-Nd-0.3Zr alloy treated by the proper annealing process first increases and then decreases with increasing of pre-deformation degree and when the annealing temperature reaches to 210?,the annealing strengthening effect will disappear.Compared with low speed compression test at room temperature,the low speed compression properties of Mg-Ca-0.3Zr alloys at high temperature(150?)have not been obviously improved.Moreover,the plastic instability occurs in Mg-Ca-0.3Zr alloys when the compression speed is higher than 0.01mm/min.In the meantime,the low speed compression at high temperature can refine the twin lamellaes in Mg-5.3Nd-0.3Zr alloys,and the twin density increase and the annealing strengthening effect becomes more obvious with increasing of the multi-axial cumulative deformation.