Grain refinement of AZ31 magnesium alloy by means of hydrogenation treatment

Abstract

To develop a fine grain structure on the surface of a magnesium alloy, a multi-axial alternative forged AZ31B magnesium alloy was subjected to hydrogenation treatment using the resultant hydrogen compounds as the trapping source for dislocations, which were induced following the application of the shot peening technique used for surface high strain working and recrystallization treatment. The effect of hydrogenation for grain refinement and the relationship of grain refinement and strength were examined. The storage hydrogen content in forged materials subjected to hydrogenation treatment is 2.1×10−1 mass%, and hydride compounds can be confirmed by X-ray diffraction down to a depth of 0.5 mm beneath the surface. Following the shot peening process, the microstructure of the forged material shows high dislocation density and the average grain size following recrystallization heat treatment is about 1 μm. It was confirmed that the hydrogen absorption process coupled with the shot peening process and recrystallization heat treatment was an effective process to increase surface strength and grain refinement in the material surface.