Effects of different cooling conditions on friction stir processing of A356 alloy: Numerical modeling and experiment

In the present work, the effects of in-process cooling are investigated on the material flow, temperature distribution, axial force, wear resistance, and microstructural and mechanical properties of friction stir processed (FSPed) Al-Si aluminum alloy. The finite element method (FEM) was developed for modeling the process, based on the eulerian-lagrangian technique, and then verified by the experimental force and temperature histories. Next, the material flow and temperature distribution during the friction stir process (FSP) with in-process cooling under different conditions were considered. After that, the experimental investigations, including the optical microscopy, hardness, and wear tests, were conducted. Finally, the stir zone (SZ) shape obtained by experiments and simulation model were compared for the FSPed samples without cooling and with air cooling. The material flow achievements reveal that using a coolant affects the material flow in the pin-driven zone more significantly than in the shoulder-driven zone, leading the SZ to change from the basin shape into the V shape. The SZ shapes obtained from the experiments and the simulation model show a good agreement between the shapes of the samples FSPed without cooling and with air cooling. Moreover, experimental results showed that using in-process cooling reduces Si particles' size and thus significantly increases the hardness and wear resistance. The Si particles size is reduced from 10 μm in the base metal to 2.6 μm and 2 μm in the air-cooled and water-cooled samples. Consequently, the wear mass loss reduced almost 28% and 40%, and hardness increased almost 35% and 80% for the air-cooled and water-cooled samples compared to the processed samples without coolant.