Microstructure, Mechanical Properties and Fracture Behavior of Micron-Sized TiB2/AlZnMgCu(Sc,Zr) Composites Fabricated by Selective Laser Melting

In this paper, micron-sized TiB2/AlZnMgCu(Sc,Zr) composites were fabricated by selective laser melting (SLM) using directly mixed powder. Nearly fully dense (over 99.5%) and crack-free SLM-fabricated TiB2/AlZnMgCu(Sc,Zr) composite samples were obtained and its microstructure and mechanical properties were investigated. It is found that the laser absorption rate of powder is improved by introducing micron-sizedTiB2 particles, then the energy density required for SLM forming can be reduced, and the densification can finally be improved. Some crystalline TiB2 formed a coherent relationship with the matrix, while some broken TiB2 particles did not, however, MgZn2 and Al3(Sc,Zr) can perform as intermediate phases to connect these non-coherent surfaces to aluminum matrix. All these factors lead to an increase in strength of the composite. The SLM-fabricated micron-sized TiB2/AlZnMgCu(Sc,Zr) composite finally shows a very high ultimate tensile strength of ~646 MPa and yield strength of ~623 MPa, which are higher than many other aluminum composites fabricated by SLM, while maintaining a relatively good ductility of ~4.5%. The fracture of TiB2/AlZnMgCu(Sc,Zr) composite is occurred along the TiB2 particles and the bottom of the molten pool. This is due to the concentration of stress from the sharp tip of TiB2 particles and the coarse precipitated phase at the bottom of the molten pool. The results show that TiB2 plays a positive role in AlZnMgCu alloys fabricated by SLM, but finer TiB2 particles should be studied.