Selective laser melting of high-strength TiB₂/AlMgScZr composites: microstructure, tensile deformation behavior, and mechanical properties

A TiB₂/AlMgScZr composite was fabricated by selective laser melting (SLM) with direct powder mixing. The microstructure and mechanical properties of SLM-fabricated TiB₂/AlMgScZr composites were investigated. Nearly fully dense and crack-free SLM-fabricated TiB₂/AlMgScZr parts were obtained. The results showed that TiB₂ formed a coherent relationship with the matrix and was swallowed by the solid–liquid interface as a nucleation point to refine grains during the SLM process. In addition, some TiB₂ particles did not form a coherent relationship with the matrix, moving the solid–liquid interface at the grain boundary, which reduced the recrystallization fraction and refined the grains significantly. TiB₂ also promoted the precipitation of Al₃Sc and Al₃Zr phases and increased the volume fraction of the Al₃Sc and Al₃Zr phases during the SLM process. The SLM-fabricated TiB₂/AlMgScZr composites showed a very high ultimate tensile strength of ∼483 MPa and excellent ductility of ∼15.8%, which are higher than those of wrought Al alloys. The solid solubility of the Mg element slightly increased in the SLM-fabricated TiB₂/AlMgScZr composites because of the high heating and cooling rate during the SLM process. The high heating and cooling rate caused discontinuous strain and Portevin–Le Chatelier effect and weakened the strengthening effect of TiB₂ in SLM-fabricated TiB₂/AlMgSc composites.