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

This paper deals with an experimental investigation 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 particles 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 mu m) and increases the hardness (from 63 to 98 HV) and strength (from 130 to 250 MPa). However, no significant difference was found in wear resistance of the specimens produced with different process parameters.