Microstructure and mechanical properties of a TiB 2-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 alpha-Al grains' mean size to be 0.64 mu m +/- 0.26 mu m TiB2 particles with sizes of several tens of nm up to 1.5 mu m were observed in the as-built component. Small TiB2 particles of up to approx. 200 nm are located within the alpha-Al grains, which show a semi-coherent interface to the alpha-Al phase. Larger TiB2 particles of up to 1.5 mu m accumulate in the liquid between the growing alpha-Al grains during solidification and inhibit grain growth. Al2Cu phase is precipitated at the alpha-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%.

Automated summary

By using laser powder-bed fusion, crack-free samples with a relative density of 99.5% were successfully produced, showing a homogeneous equiaxed microstructure with an average grain size of 0.64 µm and TiB2 particle sizes ranging from several tens of nm to 1.5 µm. The novel fine-grained microstructure resulted in a tensile strength of 401 ± 2 MPa and total elongation at fracture of 17.7 ± 0.8% in the as-built state.