Effect of FSP parameters and tool geometry on microstructure, hardness, and wear properties of AA7075 with and without reinforcing B₄C ceramic particles

The aim of this work is to produce a surface composite by incorporating B₄C particles on the surface of AA7075 alloy through friction stir processing (FSP) using both a pinless and a cone pin tool. The influence of friction stir processing parameters on the microstructure, hardness, and wear properties of the processed surface composites was investigated. The studied parameters include rotational tool speed (400 and 600 rpm) and number of passes (1, 2, 3, and 4 passes). Microstructural analysis and microhardness profiles were performed on cross sections of FSPed samples at different depths. Wear behavior of the processed samples was evaluated by means of dry sliding tests. The results indicate that (i) increasing the number of passes results in improving the distribution of B₄C reinforcing particles, (ii) samples processed with the pinless tool displayed a more homogeneous distribution of the reinforcement in the outer layer of the material with respect to the samples processed with the cone pin, (iii) the addition of B₄C particles improved the wear resistance of the AA7075 alloy even if it led to a raise in the coefficient of friction.