Tailoring the strength and formability of Mg alloys through rare earth element additions (Gd and Dy) and dynamic recrystallizations

Nowadays, the improvement of workability and strength of Mg has received increasing attention. Rare earth elements have shown great potential in refining grains, weakening sharp basal textures, and thus improving the formability of Mg alloys. Therefore, yttrium-similarity index model has been developed previously to assist to search for the effective RE elements to improve the ductility of Mg alloys. Here, a series of new Mg alloys based on Mg-Gd-Dy-Zr system have been fabricated through casting and hot extrusion processes. Noticeably, through hot extrusion, the ultimate tensile strength and elongation of Mg-1.2Gd-0.6Dy-0.2Zr (wt%) alloy are increased by ~13.2% and ~100% respectively, reaching 171 MPa and 32%. Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectrometer, and Electron Backscattered Diffraction are utilized to investigate the microstructure evolution of Mg-Gd-Dy-Zr alloys. It is found that the intensity and type of texture dominate the variation of mechanical properties. The extrusion texture undergoes the evolution from <112¯1>//ED to <0001>//ED abnormal texture with the increase of rare earth additions. The elongation increases first and then decreases, while the trend of strength variation is on the contrary. Therefore, the strength and formability can be effectively tailored to a desired value by controlling the concentration of rare earth additions and dynamic recrystallizations.