Enhanced manufacturing quality and mechanical performance of laser powder bed fused TiC/AZ91D magnesium matrix composites

The addition of ceramic reinforcements provides a promising approach to achieving high-performance magnesium matrix composites. In this work, AZ91D magnesium alloys and 2 wt.% TiC/AZ91D composites have been manufactured by laser powder bed fusion (LPBF) with variations of laser processing parameters. The effect of TiC reinforcement addition on the laser absorption behaviors, forming quality, microstructure evolution and mechanical properties of the magnesium alloys is investigated. The TiC addition improves the interactions of laser with alloy powder and laser absorption rate of alloy powder, and decreases powder spatter of powder bed. The results show that high relative density of ~99.4% and good surface roughness of ~12 µm are obtained for the LPBF-fabricated composites. The TiC addition promotes the precipitation of β-Mg₁₇Al₁₂ in the alloys and the transformation of coarse columnar to fine equiaxed grains, where the grains are refined to ~3.1 µm. The TiC/AZ91D composites exhibit high microhardness of 114.6 ± 2.5 HV_0.2, high tensile strength of ~345.0 MPa and a uniform elongation ~4.1%. The improvement of tensile strength for the composites is ascribed to the combination of grain refinement strengthening and Orowan strengthening from β-Mg₁₇Al₁₂ precipitates and Al₈Mn₅ nanoparticles. In the composites, the unmelted TiC particles can act as an anchor for the network structure of β-Mg₁₇Al₁₂ precipitates, effectively impeding crack propagation and enhancing their performance. This work offers an insight to fabricating high-performance magnesium matrix composites by laser additive manufacturing.