Solid recycling of an AZ31 Mg alloy with a vapor deposition coating layer of high purity Mg

Solid recycling of AZ31 Mg alloy with vapor deposition coating layer of high purity Mg was evaluated. In the open die forging experiments, two AZ31 Mg alloy specimens with the pure Mg deposition coating layer of the 30 put in thickness were forged. The specimens were sufficiently bonded by forging at 673 K. Furthermore, the elements (Al and Zn) of the AZ31 substrate diffused up to the center of the pure Mg deposition coating layer. The theoretical analysis in which only the lattice diffusion was considered showed that the elements in the AZ31 substrate cannot diffuse to the center of the pure Mg deposition coating layer. The grain boundary diffusion coefficient of Mg at 673 K is about 25 times larger than the lattice diffusion coefficient. Therefore, it is suggested that the grain boundary diffusion enhanced by grain refinement due to hot forging largely contributes to the solid state bonding of the forged specimens. Also, the solid recycled specimen was fabricated from the AZ31 Mg substrate with pure Mg deposition coating layer by hot extrusion at 673 K. The solid recycled specimen showed almost the same tensile properties as the virgin extruded specimen. This is probably related not only to the grain boundary diffusion enhanced due to grain refinement, but also severe plastic deformation by hot extrusion.