Effect Of Alloying Elements On Microstructure And Properties Of PM Mg Alloys

For structural components, especially the structural components requiring higher intensity, lowdensity of Mg and Mg alloys are more attractive. An important field in improving properties ofmagnesium alloys is the addition of alloying elements. In this paper, Mg alloys were fabricated bypowder metallurgy. Subsequently, effect of alloying elements Al, Zr, Si and Mn on microstructure andproperties of Mg alloys were respectively studied through OM, XRD, SEM, and various mechanicaltests.Mg-xAl-1.5Zr（x=0,2,4,6,8mass%, the same in the following） alloys were prepared by powdermetallurgy under the conditions of550℃for4h, Ar atmosphere. The microstructure of the alloy wasconsist of α-Mg matrix, β-Mg17Al12, Zr and some micro-porosities. With the increasing of Al contents,amount and size of pores decreased, and microstructure of alloys became more homogeneous.Hardness and bending strength of alloys first increased then decreased with the increasing of Alcontents. When Al content was6%, hardness and bending strength of alloy reached the highest value,being79.7HV and224MPa.Mg-6Al-xZr（x=0,3,6,9%） alloys were prepared by mechanical alloying and powder metallurgy.Mechanical alloying increased free energy of milled powder, and accelerated the subsequent sinteringprocess. Microstructure of sintered alloys under condition of550℃for4h contained Mg matrix, Zrand Mg17Al12, together with lots of micro-porosities. Increasing of Zr contents resulted in gradualdecreasing of Mg grains, together with more homogeneous of microstructure. Addition of Zr elementpromoted hardness and bending strength of alloys. Its hardness and bending strength reached thehighest values with9%Zr, being75.6HV and321.125MPa. Grains of α-Mg matrix of re-sinteredalloys at650℃and700℃were still irregular, with no obvious change. With the increasingtemperatures, amount and size of pores decreased gradually. Simultaneously, element Al diffused intoZr particles and formed Al₃Zr intermediate phase.For Mg-xSi-1.5Zr（x=1,3,6%） and Mg-xMn-1.5Zr（x=1,3,6%） alloys, no intermediatecompound was formed as a result of mechanical alloying. Mn, Si, Zr were still exist as a form ofsimple substance. The former had an appearance of Mg2Si phase after sintering, and amount of Mg2Siphase increased with the increasing of Si contents. Addition of Mn element weakened the effect ofgrain refinement. Grains of alloys slightly increased with more Mn. Bending strength and hardness ofMg-Si-Zr alloys increased with the increasing Si contents, and the value of bending strength ofMg-6Si-1.5Zr was the highest, reaching132MPa. Also, Bending strength and hardness of Mg-Mn-Zr alloys increased with the increasing Mn contents, and the value of bending strength of Mg-6Mn-1.5Zrwas the highest, reaching117.8MPa.