A study on the microstructure and properties of Al/Cu lap joints welded by friction stir brazing with ultrahigh rotation speed

摘要

Friction stir brazing (FSB) with ultrahigh rotation speed was applied to join 6061 aluminum to pure copper with the aid of zinc foil. The effects of different shoulder diameters on the microstructure and mechanical properties of Al/Cu FSB joints were investigated combined with temperature and axial force. In the joint brazed by a 7 mm diameter shoulder, the filler metal layer exhibited the original zinc. Meanwhile, a layer of thick CuZn5 was found on the Cu interface. As the diameter of the shoulder was increased to 10 mm, the homogeneous structure of Al-Zn eutectic formed at the Al-Cu interface. Further increasing the shoulder diameter to 12 mm, however, resulted in the interlayer obtaining a microstructure of Al-Zn eutectic with refined and dispersed CuZn5. When the shoulder diameter increased to 15 mm, brittle intermetallic compounds (IMCs) such as Al2Cu and Al4.2Cu3.2Zn0.7 were generated and holes appeared owing to the high-temperature and axial force. Shear tensile tests showed that the joint brazed by a 12 mm diameter shoulder achieved the highest shear tensile strength.