High Strength and Heat Resistance of Low-RE-Containing Mg Alloy Achieved via Substantial Dynamic Precipitates

Conventional high-strength Mg-RE-based wrought alloys usually contain a high amount of RE solutes, which largely increases the alloy cost and thus restricts their adoptions. In this work, we developed a low-RE-containing Mg-3Sm-1Nd-0.6Zn-0.4Zr alloy by hot extrusion with low extrusion ratio, which shows a high tensile yield strength (TYS) of 435 MPa and a satisfactory elongation of 5.6% at room temperature, outperforming most Mg-Gd-Y-based extrusion alloys with RE contents of 12 wt% at least. Outstanding high-temperature strength, such as the TYS of 280 MPa at 200 °C and 251 MPa at 250 °C, is also obtained in this alloy. The alloy presented a typical bimodal grain structure including coarse hot-worked grains with a strong texture and fine recrystallized grains with random orientations. Also, abundant Mg₃RE particles were mostly introduced in hot-worked grains and at recrystallized grain boundaries by dynamic precipitation during extrusion. Consequently, the high strength of this alloy is principally attributed to the combined hardening effect of numerous Mg₃RE particles, fine recrystallized grains, and strongly textural hot-worked grains, rather than the ultra-strong age-hardening effect in traditional high RE-alloyed Mg alloys.