Microstructure and mechanical properties of a TiB₂-modified Al–Cu alloy processed by laser powder-bed fusion

In this work, crack-free samples with a relative density of 99.5 ± 0.1% were produced from a gas-atomized Al–Cu–Ag–Mg–Ti–TiB₂ powder via laser powder-bed fusion. The homogeneous equiaxed microstructure without preferred grain orientation shows the α-Al grains’ mean size to be 0.64 μm ± 0.26 μm TiB₂ particles with sizes of several tens of nm up to 1.5 μm were observed in the as-built component. Small TiB₂ particles of up to approx. 200 nm are located within the α-Al grains, which show a semi-coherent interface to the α-Al phase. Larger TiB₂ particles of up to 1.5 μm accumulate in the liquid between the growing α-Al grains during solidification and inhibit grain growth. Al₂Cu phase is precipitated at the α-Al grain boundaries. Coarse Al₂Cu precipitates, which are slightly enriched with silver and magnesium, are also observed within the grains preferentially precipitated on small pores and TiB₂ particles. The novel fine-grained microstructure results in the as-built state in a tensile strength of 401 ± 2 MPa and total elongation at fracture of 17.7 ± 0.8%.