From gradient to homogenous: thermal behavior-induced microstructure evolution and mechanical properties of selective laser-melted TiB_2p/2024Al composite

As one of the important additive manufacturing techniques, selective laser melting (SLM) has shown great advantage in the production of metal matrix composite components with complex geometry. However, the layer-by-layer manufacturing procedure causes a nonnegligible thermal accumulation and cycling. Thus, the SLM-deposited component always presents gradient microstructure and mechanical properties. In this work, the dense TiB_2p/2024Al composite prepared by SLM was employed to investigate the heat-induced microstructure evolution and mechanical properties. The as-deposited composite presents a uniform distribution of TiB₂ reinforced particle in α-Al matrix with an oriented < 100 > texture α-Al dendrite microstructure. The yield strength (YS), ultimate tensile strength (UTS), and the elongation of as-deposited sample increase from 230.06 MPa, 302.52 MPa, and 4.49% to 244.17 MPa, 365.36 MPa, and 11.48% from the bottom to top regions. According to the TEM results, this phenomenon is attributed to the high cooling rate induced low content of θ-Al₂Cu phase at the bottom of the sample. In addition, agglomeration of the TiB₂ particles due to the insufficient convention is responsible to the poor elongation at the bottom of the sample. After the solid solution and aging heat treatment (T6), thanks to the uniform distribution of S strengthening phases, this gradient in microstructure and mechanical properties in the deposit can be eliminated, and the deposit presents higher YS, UTS, and a lower elongation of 380.23 MPa, 421.50 MPa, and 3.14%.