A magnesium alloy with ultrahigh Gd content manufactured by laser directed energy deposition: Heat treatment and microstructure evolution

High RE content is able to improve the age-hardening response of Mg–RE alloys, thus enhancing mechanical properties. Here, we successfully produce a Mg–22Gd–2Zn–0.4Zr (wt%) alloy with ultrahigh Gd content using laser directed energy deposition (LDED) and investigate the microstructure evolution during heat treatment. Results show that for the studied alloy, the yield strength is 333 MPa after solution at 520 °C for 2 hours and aging at 200 °C for 64 hours, superior to most existing Mg–Gd alloys, due to the high number density of the strengthening β' phase resulting from high supersaturation. During solution treatment, increasing the temperature improves the solution efficiency by reducing the holding time, while preventing the overgrowth of grains. The peak hardness is around 139 Hv for both 175 °C and 200 °C aging, indicating that the peak hardness of Mg alloys with high Gd content is insensitive to aging temperature. This research can serve as guidance for the heat treatment and microstructure control of high-Gd-content magnesium alloys.