Grain refinement and crack inhibition of selective laser melted AA2024 aluminum alloy via inoculation with TiC–TiH2

Abstract

AA2024 aluminum alloy easily forms coarse columnar grains and cracks during selective laser melting (SLM). Herein, a novel grain refiner composed of TiC nanoparticles and TiH2 powders was used to develop the microstructure of selective laser melted AA2024 aluminum alloy. Due to the heterogeneous nucleation of α-Al promoted by the cooperation of TiH2 and TiC, the microstructure of the TiC–TiH2/AA2024 composite converted from columnar grains with an average area of 729.0 μm2 into equiaxed grains with an average area of 3.4 μm2, and the morphology of the second phase changed from streamline to network-shaped. Moreover, cracks in the TiC–TiH2/AA2024 composite were intrinsically eliminated because of grain refinement. Benefitting from elimination of columnar grains and inhibition of cracks as well as the combined effect of refinement strengthening and Orowan strengthening, the TiC–TiH2/AA2024 composite exhibited excellent mechanical properties, the tensile strength and elongation of as-built samples rose from 240 ± 10 MPa and 0.3 ± 0.2% in AA2024 alloy to 390 ± 15 MPa and 12.0 ± 0.5% in TiC–TiH2/AA2024 composite. After T6 heat treatment, TiC–TiH2/AA2024 composite exhibited a tensile strength of 490 ± 20 MPa and elongation of 16.0 ± 1%, which were comparable to those of wrought AA2024 alloys. The results show that aluminum alloy with excellent mechanical properties can be prepared by SLM with effective microstructure control.