Microstructural, Mechanical and Wear Properties of Friction Stir Welded AA6061/AlN_p Composite Joints

Friction stir welding (FSW) process is an appropriate welding process to successfully join the aluminum matrix composites (AMCs) reinforced with ceramic particles. In this study, AA6061 AMCs reinforced with 10 and 20 weight percentages of aluminum nitride particles (AlN_p) were welded by FSW process. The effect of FSW on microstructure, microhardness and tensile strength of AA6061/AlN_p composite joints as well as wear behavior of the weld zone (WZ) was analyzed. It was found that reinforcement particles were broken and fragmented in the weld zone of FS-welded composite joints. Microhardness of the weld zone was higher compared to other metallurgical zones. Average microhardness at the WZ of AA6061/20 wt.% AlN_p composite was 134 HV which is 36% higher than that of its base composite. It was observed that grain size of the AA6061 matrix was refined at the WZ. Average grain size of AA6061 alloy was 138 µm which was reduced to 3.8 µm at the WZ of AA6061/20 wt.% of AlN_p composite joint. Around 90% of the particles size in the WZ was reduced to less than 5 µm from the relatively large size existed in the base composite. Ultimate tensile strength of FS-welded AA6061 alloy was 151 MPa which increased to 231 MPa in FS-welded AA6061/20 wt.% AlN_p composite joint. Wear rate of FS-welded composite joints was less than that of its corresponding base composites under the same wear testing conditions. Average coefficient of friction at the WZ of FS-welded AA6061 alloy and AA6061/10 and 20 wt.% AlN_p was found to be 0.41, 0.33 and 0.22, respectively. Wear mechanism of FS-welded joint was characterized to be abrasive.