Effect of T6 heat treatment on microstructure and mechanical properties of Hf-modified Al7075 alloy fabricated by laser powder bed fusion

Very recently, we have proposed a new Hf-modified Al7075 alloy, which was demonstrated to have good compatibility with laser powder bed fusion (LPBF) processing. The present work has further explored the response of the microstructure and mechanical properties of the alloy to a T6 heat treatment (solution treatment at 470 °C for 1 h + aging at 120 °C for 24 h). It was found that after the heat treatment, Al₃Hf precipitates have experienced a huge change, from a spheroidal form with an L1₂ structure to a needle-like form with a D0₂₂ structure, whereas the grain morphology, size, orientation have little been altered. Meanwhile, the strength of the alloy has obviously been improved without losing much of the ductility after the heat treatment. The improvement of the strength is mainly attributed to the produced D0₂₂-Al₃Hf particles, which have an unexpected coherent interface with the α-Al matrix, a large volume fraction, and a small radius of the repeated building blocks.