| dc.description.abstract | In this work, main similar (6061 aluminum alloy) and dissimilar (commercially pure aluminum and copper) materials were butt joined via friction-stir welding (FSW). The influence of FSW parameters, namely, small pin geometry, rotational speed, welding
speed, and surface roughness of material, on the macrostructure, microstructure, and mechanical properties of only similar material joint characteristics were evaluated. The effects of FSW tool rotational speeds, with and without preheating on the copper side for dissimilar material joints, were also examined. For tool pin geometry, the triangular tool pin profile produced the most feasible metallurgical and mechanical weld properties among other tool pin profiles. Furthermore, the lowest tensile strength and
microhardness were obtained for the joint FSW with square tool pin profile. Smaller tool pin profiles and shoulder diameter led to narrow heat-affected zone (HAZ) and a desired softening level. The 6061 aluminum alloy workpieces stirred by friction were
welded at different tool rotational speeds and treated with and without reinforcement of 10 vol. % SiC powder from the welding volume. The results indicated the presence of the optimal mechanical properties when the joint was fabricated at 1750 rpm rotational speed because of the pinning effect and enlarged nucleation sites associated with the insertion of SiC powder in the welding zone. The results also revealed that the ultimate tensile strength (UTS) was significantly enhanced by approximately 52% of the base material (6061 aluminum alloy), at 1750 rpm because of the effect of the SiC powder. All process parameters used in this research significantly affected the microstructure and mechanical properties. The results also indicated that the welding speed
significantly influenced the joint microstructure and mechanical properties when reinforced with SiC powder. Results demonstrated that spherical nano-sized grains of the joints were produced when the top surface of the workpieces ground smoothly (i.e.98, 60, 51 and 37 nm). Experimental results also indicated that the tensile strength of FSW 6061 aluminum alloy was notably affected by the joining process at different selected values of workpiece surface roughness. However, Vickers microhardness was improved in the HAZ because of the effect of surface roughness, which narrowed the width of this zone. The FSW of commercial pure aluminum and copper demonstrated high bonding strength when preheated on the copper side compared with the optimal joint of the specimen conducted without preheating. Furthermore, X-Ray Diffraction (XRD) data showed that changes in metal alloy crystallite sizes, densities, and lattice parameters occurred over the test distances at different rotational speeds. The grains were fine and dynamically recrystallized near the weld interface and elongated at various distances. The fracture surfaces showed varied results when different parameters were used. These surfaces presented either ductile or brittle fracture. | en_US |
