Development of low rare-earth containing magnesium alloy with high strength-ductility synergy by engineering nano-spaced lamellae

Abstract

Conventional Mg-RE-based alloys containing a high content of RE solutes can generate high strength, but there is often low ductility. Herein, we reported a low RE alloying Mg–5Er-1Nd-1Zn-0.2Zr extrusion alloy with only 6 wt% RE addition, showing a high strength-ductility synergy, such as a yield strength of ∼380 MPa and an elongation of ∼12.5 %), which is superior to the majority of traditional Mg-RE-based wrought alloys with at least 12 wt% RE addition. Nano-spaced lamellae was formed in the α-Mg matrix during extrusion, such as stacking faults (SFs) evolved in dynamically recrystallized (DRXed) grains and the 14H long-period stacking-ordered (LPSO) phase developed in unDRXed grains as a result of dynamical solute partitioning during extrusion. And this alloy characterizes a high proportion (∼70 %) of elongated unDRXed grains with a strong basal texture. Thus, high strength is mostly related to SFs/LPSO lamellae strengthening and texture hardening, instead of the commonly accepted refinement strengthening and precipitation hardening in those of high RE containing Mg alloys. While high ductility is heavily dependent on SFs/LPSO lamellae to trigger strain hardening and dislocations glide, independent of fine grains as in traditional Mg alloys with high elongation. The findings give an insight into the development of high-performance Mg wrought alloys with a high strength-ductility synergy.

Keywords

• Mg-RE alloys
• Strength-ductility synergy
• LPSO/SFs
• Microstructure