Microstructure, Mechanical Properties and Fracture Behavior of Micron-Sized TiB(2)/AlZnMgCu(Sc,Zr) Composites Fabricated by Selective Laser Melting

In this paper, micron-sized TiB(2)/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 TiB(2)/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-sizedTiB(2) particles, then the energy density required for SLM forming can be reduced, and the densification can finally be improved. Some crystalline TiB(2) formed a coherent relationship with the matrix, while some broken TiB(2) particles did not, however, MgZn(2) and Al(3)(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 TiB(2)/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 TiB(2)/AlZnMgCu(Sc,Zr) composite is occurred along the TiB(2) particles and the bottom of the molten pool. This is due to the concentration of stress from the sharp tip of TiB(2) particles and the coarse precipitated phase at the bottom of the molten pool. The results show that TiB(2) plays a positive role in AlZnMgCu alloys fabricated by SLM, but finer TiB(2) particles should be studied.