Customized heat treatment process enabled excellent mechanical properties in wire arc additively manufactured Mg-RE-Zn-Zr alloys

Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials, especially for the alloys with complex phase constituents and heterogenous microstructure. However, the interrelated evolutions of different microstructure features make it difficult to establish optimal heat treatment process. Herein, we proposed a method for customized heat treatment process exploration and establishment to overcome this challenge for such kind of alloys, and a wire arc additively manufactured (WAAM) Mg-Gd-Y-Zn-Zr alloy with layered heterostructure was used for feasibility verification. Through this method, an optimal microstructure (fine grain, controllable amount of LPSO structure and nano-scale β' precipitates) and the corresponding customized heat treatment process (520 °C/30 min + 200 °C/48 h) were obtained to achieve a combination of a high strength of 364 MPa and a considerable elongation of 6.2 %, which surpassed those of other state-of-the-art WAAM-processed Mg alloys. Furthermore, we evidenced for the first time that the favorable effect of the undeformed LPSO structure on the mechanical properties was emphasized only when the nano-scale β’ precipitates were present. It is believed that the findings promote the development of advanced Mg alloys and help to establish customized heat treatment process for additively manufactured materials.