Research On Processing And Mechanism Of AZ91d Magnesium Alloy By Selective Laser Melting

Magnesium and its alloys have been widely used in automobile, electronics,aerospace, military industries and so on due to their excellent specific strength, specificstiffness, electromagnetic shielding and radiation resistance. However, the deformabilityof magnesium alloys in room temperature is poor due to the hcp structure, which limits theabilities to forge complex parts. Moreover, there are many defects in casted magnesiumalloys such as coarse grains, shrinkage, inclusions and so on. Selective laser melting(SLM) is regarded as a new way to fabricate magnesium alloys because nearly any shapeof SLMed parts with excellent performances and high precisions can be produced withoutlimitation.In this paper, AZ91D magnesium alloy powers are used as the starting material andthe effects of parameters, such as laser power, scanning speed and scanning line space onthe ablation of elements, phases and the relative density have been investigated,respectively. Moreover, microstructure, composition distribution and microhardness of theSLMed samples at optimal processing parameters were tested.The main results are as follows:(1) The ablation of Mg element increases with thelinear energy. The extent of ablation has nothing to do with the types of phase butincreases the lattice distortion of the α-Mg.(2) The scanning speed plays the most key roleto influence the densities of SLMed samples. The relative density higher than99%can beobtained at a linear energy from6.6J/cm to12J/cm and a scanning line space of50～80μm. In our experiments, the optimized processing parameters are laser power170W,scanning speed10m/min, scanning line space50~80μm.(3) The grain sizes of the SLMedsamples at the optimal processing parameters is only2to3μm. Elements of Mg, Al, Zndisperse in the matrix uniformly and the content of Al concentrates at the grain boundaries.Finally, the average microhardness of110Hv can be reached for the SLMed AZ91Dsamples.