The effects of Pass number and Nano-Size ZrO2 powder on the Mechanical, Microstructure and Wear behavior in Friction Stir Welding of the Al-5083

In this study friction stir welding was used to perform butt joint of Al5083 and simultaneous production of Al-ZrO2 nanocomposite in weldment. Welding parameters such as rotational speed, travel speed and tilt angle were varied to obtain optimum weldment with no defect and high tensile strength, and then by adding zirconia nanoparticle to welding zone of optimum sample, the effects of pass number on microstructure, mechanical properties and wear characteristics of welded specimens were investigated. In order to investigate microstructure, optical and scanning electron microscope and atomic force microscope was used. Results showed that by increasing pass number, the distribution of nanoparticles in the matrix become more homogenous and grain size in the stir zone has considerably decreased. The reason of this phenomena could be attributed to the presence of reinforcement nanoparticles which it causes pinning the grain boundary, enhancing nucleation of new recrystallized grains and the effect on breaking of initial grains. The maximum microhardness and tensile strength of weldment were obtained for composite weldment after four pass of 111 Hv and 328.3 MPa, which these values were 24 and 26% higher than weldment without reinforcement. Wear resistance of the weldment was determined by pin on disk test and revealed that by increasing pass number of FSW, the wear resistance increased.