Incorporating oxygen-free copper to improve the microstructure and mechanical properties of friction-stir-welded joints for aluminum alloys

The main objective of the present work was to establish a friction-stir-welding process to weld dissimilar metal joints on AA6082 and AA6066 aluminum alloy plates. Joints were made while varying tool rotation speed at a constant traveling speed and at the same time adding oxygen-free copper reinforcement inside the weld nugget for the purpose of analyzing the microstructural evolution and mechanical properties of the joint. Results showed that the morphology of the microstructure in the weld nugget changed significantly with rotation speed. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy analyses revealed that oxygen-free copper particles could be uniformly dispersed into the weld nugget because of higher rotation speeds. Because of the presence of reinforcement particles homogenously distributed inside the nugget zone, the mechanical properties, such as ultimate tensile strength and hardness of weld joint, were greatly improved.