In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting (SLM) was employed to achieve nearly full dense and crack-free AZ91D components with fine equiaxed grain structure. The formation mechanism of typical pore defects (gas pore, lack-of-fusion pore and keyhole pore) and melting modes (keyhole mode and conduction mode) were systematically studied by varying the laser power and scanning speed. The morphology and volume fraction of the pores under different processing conditions were characterized. A criterion based on the depth-to-width ratio of the melt pool was established to identify different melting modes. The strength and ductility (tensile strength up to 340 MPa and uniform elongation of 8.9%) of the as deposited AZ91D are far superior to those of the casting components and are comparable to those of its wrought counterparts. The superior balance of strength and ductility of SLMed AZ91D, as well as the negligible anisotropic properties are mainly ascribed to the extremely fine equiaxed grain structure (with average grain size of ∼1.2 µm), as well as the discontinuous distribution of β-Al₁₂Mg₁₇ phases. It thus provides an alternative way to fabricate high-strength magnesium alloys with complex geometry.

在全球碳中和的背景下，轻质镁合金的应用越来越有吸引力。在这项研究中，采用选择性激光熔化（SLM）来获得具有细等轴晶结构的几乎全致密且无裂纹的 AZ91D 部件。通过改变激光功率和扫描速度，系统研究了典型孔隙缺陷（气孔、未熔合孔和匙孔）的形成机制和熔化模式（匙孔模式和传导模式）。对不同加工条件下孔隙的形貌和体积分数进行了表征。建立了基于熔池深宽比的标准来识别不同的熔化模式。沉积态 AZ91D 的强度和延展性（抗拉强度高达 340 MPa，均匀伸长率为 8.9%）远远优于铸造部件，与锻造部件相当。SLMed AZ91D 的强度和延展性的优异平衡以及可忽略不计的各向异性性能主要归因于极细的等轴晶结构（平均晶粒尺寸约为 1.2 µm）以及 β-Al 12 的不连续_分布镁₁₇相。因此，它提供了一种制造具有复杂几何形状的高强度镁合金的替代方法。