Friction stir welding of foamable AlSi7 reinforced by B4C

Friction stir welding was successfully performed on B4C-reinforced foamable AlSi7 materials produced via a powder metallurgy route. Starting materials of 1 wt.% TiH2, 7 wt.% Si and 6 wt.% B4C were mixed with aluminum matrix powder. Mixed powders were then pressed, extruded and rolled for the production of foamable materials. Microstructural and macrostructural examination along with microhardness and tensile tests were performed to evaluate the weld zone characteristics of foamable materials welded by friction stir welding. Tunnels or needle-shaped gaps were observed in the macrostructures of the weld zones of samples joined at 1 250 rpm and 2 000 rpm rotational speeds. Moreover, the rough surface in the welding zone of materials decreased with increasing rotational speed. Defect-free joints were observed for samples at 1 600 rpm rotational and 40 mm min(-1) traverse speeds. There was no significant difference between the microstructures of the weld zone and the base material in terms of particle size and distribution. It was observed that the (BC)-C-4 particles in the nugget zone were partly directed or clustered as a result of the physical mixing. Ultimate tensile strength values of (BC)-C-4-reinforced foamable AlSi7 materials joined by friction stir welding were found to be lower compared to the base material. The maximum ultimate tensile strength of 135 MPa was obtained at a 1 600 rpm rotational speed and 40 mm min(-1) traverse speed. The minimum tensile strength in the samples of 95 MPa was obtained at a 1 250 rpm rotational speed and 80 mm min(-1) traverse speed. In all welding conditions, the hardness in the nugget zone increased compared to the base material.