Surface modification of Aluminium alloy (7xxx series) by multipass friction stir processing

Multipass friction stir processing (MP-FSP) is a solid-state surface modification technique, which was developed based on the simple principle of FSW. Aluminium plates were subjected to MP-FSP from 1 to 14 passes along the longitudinal direction with the specified process parameters such as rotational speed of 1000 rpm and travel speed of 70 mm/min and axial force of 15 kN. Subsequently, similar process parameters had followed by doublepass friction stir processing (DP-FSP) in order to help determine the effectiveness of multipass in creating high strength of aluminium alloys. Now-a-days extensive research had focused on various process parameters such as rotational speed, traverse speed, tool design on processing of aluminium alloys and proficiently enhanced material properties. This technique has considered mostly development of green technology, which is energy efficient and environment friendly technique. Experimentally proven that the Al-Zn-Mg-Sc alloys are characterized through OM, FESEM, DSC, SEM, TEM, and mechanical properties. The tensile strength and ductility of the MP-FSP specimen improved significantly to 122.48%, and 42.55% respectively, but hardness decline to 4.84% as compared to DP-FSP. This is due to not only for refinement of cast dendritic structure and eliminate segregation in the as-cast alloy, but also to the refining of grains, such as the uniform distribution of Al3Sc and hardening precipitates. To aim of this research work is to mainly focusing on MP-FSP may enhance mechanical properties better than DP-FSP and useful for macroscale applications.