Influence of heat treatment on microstructure evolution and mechanical properties of TiB2/Al 2024 composites fabricated by directed energy deposition

Abstract

The influence of heat treatment on microstructure evolution and mechanical properties of TiB2/Al 2024 composites fabricated by laser-powder directed energy deposition (DED) were investigated. The results showed that the addition of TiB2 resulted in a significant grains refinement with random orientation. Compared with DED-Al 2024, a lot of network-like θ-Al2Cu phases was generated in the as-deposited TiB2/Al 2024 composite, leading to low plasticity. After 10h solution treatment, the θ phase disappeared, the thermally stable block T-Al20Cu2Mn3 phase was formed and the ultimate tensile strength (UTS) and elongation improved due to solution strengthening. During the aging process, Cu element was precipitated and semi-coherent θ’ phase was generated, improving the effect of Orowan strengthening. The composite material reached the maximum UTS of 453.65 MPa after 10h aging. The yield strength (YS) enhanced with the increase of aging time. After 15h aging, the YS and microhardness reached the maximum of 245.73 MPa and 133.50HV, respectively. This research provides a theoretical basis for the repair and manufacture of Al 2024 alloy and composite parts.