Investigating the effect of tool dimension and rotational speed on microstructure of Al-B4C surface composite layer produced by friction stir processing (FSP)

Friction stir processing (FSP) was used for the fabrication of Al-B4C surface composite. Al-Mg-Si alloy was considered as the substrate and B4C particles were incorporated into the substrate by thermo-mechanical effect of FSP. The effect of tool dimensions and different rotational speeds on the microstructure and microhardness of the composite layers was evaluated and the optimum process parameters were determined. Microstructural evaluation of the samples after FSP was conducted by optical microscopy (OM) and scanning electron microscopy (SEM) of the cross-sections of surface composite layers fabricated by FSP. Hardness profiles were obtained from microhardness measurements across the cross-sections of FSPed samples. The results showed that by increasing the tool size and rotational speed the size of nugget zone increases and the volume fraction of reinforcing particles decreases in FSPed samples. Moreover, composite layers containing higher volume fractions of B4C particles obtained from smaller tool size, exhibited higher values of hardness.