Layered Microstructure Generated by Multipass Friction Stir Processing in AZ91 Alloy and Its Effect on Fatigue Characteristics

摘要

Layered microstructure with three different configurations was developed by multipass friction stir processing (FSP) on as-cast (AC) AZ91 magnesium alloy using three different tools with probe lengths 7, 5 and 4 mm. They were half thickness processed (HFSP), surface modified (SFSP) and full thickness processed (FFSP). FSP was performed at tool rotation rate of 720 rpm and transverse speed of 150 mm/min. The large β-Mg_(17)Al_(12) particles with an average size of 20 μm and α-Mg matrix grains of 100 μm were reduced to approximately 1 and 2 μm, respectively, after multipass FSP. Texture of FSPed samples measured by X-ray diffraction technique had shown basal texture. Constant amplitude axial fatigue test was performed on all the microstructural configurations, with process direction parallel to loading axis. Life of the fatigue tested samples was found to increase with the increasing fraction of FSPed region in AZ91 alloy.