| The research and application of magnesium alloys are greatly accelerated with theincensement of traditional mineral resource consumption and development of new technology.Powder metallurgy is one of the main methods for magnesium alloy production. It is suitablefor components adjustment and producing high grade magnesium alloys. In this study, themicrostructure and the properties of magnesium alloys are studied under different techniqueparameters, such as cold pressing pressure, sintering temperature, heat treatment time. Theeffect of alloy elements on the microstructure and properties of magnesium alloys is studiedby adding different amount of alloy elements. The principle of reinforcement of differentalloying elements on the mechanical properties of magnesium alloy was discussed in detail.The effect of reinforcements on the microstructure and properties of magnesium alloys wasstudied by electron microscopy, x-ray X-ray diffraction (XRD) and scanning electronmicroscopy (SEM).It is shown from controlling the powder metallurgy process parameters: as the coldpressing pressure reaches320MPa, the hardness and yield strength reached the highest value,58.8HV and215MPa. When the sintering temperature increase, the hardness of the alloyincrease accordingly and at580℃reaches the maximum value62.7HV. More than580℃, thehardness drops down with the temperature further increase. As heat treatment time increase,the reaction among raw materials, grain boundary migration and grain growth are improvedapparently. And help the diffuse way changes from the surface diffusion to the volume change.With the improvement of sintering process parameters, the matrix pore number and size aredecreased; the pore changes from unicom to semi closed or closed, the density increased, andbecomes more homogeneous.The alloy elements have apparent influence of on microstructure and properties ofmagnesium alloy. After adding Al in the alloy, β-Mg17Al12and small amount intermediatephase of Al2Mg appeared in the microstructure. The number of pores in matrix is decreased asadding more Al in the alloy. The mechanical properties of the alloy can be effectivelyimproved with the increase of Al content. When the amount of Al increased to9%, thehardness of the alloy was the highest,58.5HV; the yield strength reached a maximum value,264MPa, when the Al content increased to8%. When the amount of Al further increases, theyield strength decreases because of the β-Mg17Al12precipitated phases increased. The phasesin the microstructure of alloy are α-Mg, Mg2Si and a small amount of MgO and MgZn afteradding Si element. As Si element in the alloy increases, the ratios of Mg2Si phase increaseaccordingly. The hardness of the alloy also increased as more Si element in the alloy, and thehighest value was reaching63.4HV. When the amount of Si element further increases, theMg2Si phase appears and clusters apparently, the microstructure uniformity is worse. Afteradding Ca element, the microstructure is mainly composed of the α-Mg matrix, MgO, MgZn phase. With the increase of Ca element, the hardness of the alloy is increased gradually andreached the highest value at0.6%,49.5HV. As the Ca element is further increased, it is easyfor Ca2Mg6Zn3gathering on grain boundary, which decreases the mechanical properties of thealloy.The effect of reinforcement phase on microstructure and properties of Mg-9Al-Zn-x%SiC（x=0,2,4,6,8%）were investigated in this study. The addition of SiC particles canobviously improve the alloy hardness and yield strength, when the ratio of SiC reached6%,the hardness and the yield strength is increased about19.6%and22.7%respectively.Reducing the SiC particle size can enhance the dispersion degree of SiC particles in themagnesium alloy and improve the uniformity and density as well as the mechanical propertiesof the alloy. When the SiC particle size increased to4000mesh, the hardness and yieldstrength are70.2HV and315MPa, have reached the maximum value. In addition, the wearresistant properties of magnesium alloy decreases first and then increases as the reinforcementphase particle mesh size decreased. |
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