Microstructure and mechanical properties of dissimilar barrier butt joints of AA6061/SiC/55p to AA2024 in friction stir welding

Dissimilar barrier butt joints of SiC particles reinforced aluminum matrix composites with a volume fraction of 55% to 2024 aluminum alloy were fabricated by friction stir welding. Investigation of microstructure and mechanical properties of the joint was conducted. Results show that, a large amount of small SiC particles, with a strip-shaped distribution, was found in the advancing side in SAZ. Microstructure features of the weld in direction of weld thickness changed a lot in WNZ1, which at the lower side was the interval distribution of large SiC particles riched bands and small SiC particles riched bands. Grain size of the upper side was larger than that of the lower side in WNZ2, while grains surrounded by SiC particles were prone to grow larger. Bonding level of the material was different in different locations in IZ, which was affected also by debris fallen from the welding tool. A higher tensile strength was obtained in rotational speed of 750 r/min, 83.1% that of the composite base material. Fracture mode of the joints was detected to be the the matrices fracture and matrices segregation to SiC particles.