On the defect formation during laser powder bed fusion of high-fraction SiC particle reinforced AlMgScZr composites

Laser powder bed fusion (LPBF) of SiC particle-reinforced aluminum matrix composites (PAMCs) is extensively utilized in aerospace and electronic device fields. High-fraction SiC-PAMCs exhibit superior intrinsic properties, but their mechanical performance is significantly compromised by defect formation. This study investigates the effect of SiC on the powder spreading behavior, melt pool characteristics, and defect formation during the LPBF of SiC/AlMgScZr composites. The results reveal a strong negative correlation exists between SiC fraction and the achievable relative density of the composites. Specifically, low-fraction SiC-PAMCs (≤2 wt%) achieve excellent powder bed homogeneity and melt pool stability, achieving relative density exceeding 98 %. In contrast, increasing the SiC fraction to 10 wt% induces severe powder agglomeration, which promotes the formation of lack-of-fusion defects and significantly reduces the relative density. This phenomenon originates from two aspects: powder spreading and fusion. The interplay between recoater blade-pushing force, interparticle cohesion, and friction, creating alternating agglomeration and cavity zones in powder bed. During laser processing, unmelted powder and SiC particle agglomerates are present within the agglomeration zones. While elevated laser power partially penetrates agglomerates, it cannot fully counteract agglomeration-induced defects. The critical fraction of SiC is 7.17 wt% under an acceptable relative density of 98 %. To break through the critical value, we recommend changes in powder mixing techniques, powder spreading strategies, and fabrication approaches. Within the current framework, this study provides qualitative guidance for practical production and establishes the foundation for further optimization of process parameters and composite design in LPBF-fabricated high-fraction PAMCs.