Microstructure and Mechanical Properties of Ultrasonically Assisted Brazing of Dissimilar Cu-Al Alloys

An ultrasonic assisted brazing method, without flux and conducted in air, was developed to braze dissimilar copper-aluminum (Cu/Al) alloys. The microstructure and properties of Cu/Al joints of Sn-9Zn eutectic solder with different parameters were studied. The results show that the Intermetallic Compound (IMC) of the Sn-9Zn/Cu interface is mainly composed of Cu5Zn8 and Cu6Sn5. According to first-principles calculations, the covalent bond formed by Cu and Zn atoms in Cu5Zn8 is weak, whereas the covalent bond formed by Cu atoms and Sn atoms in Cu6Sn5 is strong. In the absence of ultrasonically assisted brazing, the shear performance of the joint at 220 degrees C is 21.8 MPa. At the same temperature, the performance of the joint with the ultrasonically bonded 10 s is 36.8 MPa, which represents an average increase of 68% compared to the non-ultrasonic welding joints.