Research On Microstructure, Properties And Alloying Of Magnesium Alloys

Magnesium alloys are qualified as ideal materials for lightweight constructions because they offer numerous merits in physical,mechanical and casting properties:high specific strength and stiffness,excellent castability,low density,high damping capacity,good thermal and electrical conductivity etc.In recent years,magnesium alloys have been widely used as the light structure materials in the aerospace,automobile industries and electronic industry, On the other hand,wrought magnesium alloy based on microstructure refinement is the chief orientation enhancing the strength and deformability of Mg alloys.In this paper,grain refinement of Mg-6Al and AZ31 alloys of Mg-Al system have been studied,and the reaseach focused on the effects of solute element Ca on microstructure and mechanical properties of the Mg-Al based alloy.The relationship between the chemical compositon,microstructures and mechanical properties of Mg-Al based alloy were discussed to improve their mechanical properties.The influences of Ca on the microstructure of Mg-6Al and AZ31 alloys have been investigated by using optical microscope(OM),scanning electron microscope(SEM),and X-Ray diffraction and so on.The results demonstrate that Ca element can form a new Al₂Ca phase,reduce the quantity ofβ-Mg₁₇Al₁₂ phase and refine the grain in both Mg based alloys. The average grain size of Mg-6Al-3Ca alloy reduced from 163.3μm of Mg-6Al to 71.4μm, and that of AZ31-1.54Ca also decreased from 194.5μm of AZ31 to 63.4μm.The grain refinement mechanics of Ca on Mg-6Al and AZ31 can be attributed to two aspects:Ca at the solid/liquid interface front during solidification strongly restricts the grain growth of a-Mg phase,on the other hand,the formation of primary Al₂Ca phase,which acts as heterogenous nucleus.The tensile tests in the investigated range show that addition of a little Ca can improve tensile strength of as-cast Mg-6Al at room temperature and also increase significantly its elongation.However,with more than 1%Ca addition to the as-cast Mg-6Al alloy,its mechnical properties decrease.A little Ca can also increase the ultimate strength of AZ31,but if the addition is more,the mechnical properties begin to decrease.Both of Mg-6Al and AZ31 alloys with Ca are improved in microhardness.Effects of Zr on microstructures and properties of AZ31 alloy are also investigated using electromagnetic suspension casting technology.Mechanical properties are improved because of the addition of Zr.However,the concent of Zr in the detection is very little,the grain refinement and strengthening of Zr addition to AZ31 alloys are not sure in this paper at present.