On the role of cooling and tool rotational direction on microstructure and mechanical properties of friction stir processed AZ91

Abstract

This paper deals with an experimental investiga- tion focused on the effects of water cooling treatment, friction stir processing pass number, and tool rotational direction on the microstructure and mechanical properties of friction stir processed AZ91 magnesium alloy. Specimens were produced using different combinations of process parameters. Parallel to increasing the amount of oxide par- ticles in the processed area, water cooling was found to reduce the final grain size and enhance their hardness and strength. Changing the rotational direction in each pass reduces the grain size severely (from 150 to ~4 μm) and increases the hardness (from 63 to 98 HV) and strength (from ~130 to ~250 MPa). However, no significant differ- ence was found in wear resistance of the specimens pro- duced with different process parameters.