Behavior Of Intermetallic Compounds On Interfaces Of Cu-al Ultrasonic Aided Brazing Joints

The main problem of joining copper and aluminum is intermetallic compounds on joining interfaces, which is usually fragile. The main purpose of this study is to reveal the mechanism how interfaces connect with each other and mechanical behavior of intermetallic compounds on the interfaces. A new way to join copper and aluminum was proposed.A series of Sn-Zn solders were used and ultrasonic aided brazing technology was employed to investigate structure and joining mechanism on the copper-solder and aluminum-solder. It is found that, when pure Sn, pure Zn and Sn-xZn are used as solders, aluminum join with solder with solid solution interfaces, while copper join with solder through chemical reaction with intermetallic compounds on interfaces. Intermetallic layers on copper are mainly made of Cu-Sn intermetallic compounds with low brazing temperature and short brazing time, and Cu-Al-Zn ternary intermetallics with high brazing temperature and long brazing time. As more aluminum dissolve into solders and more aluminum and zinc segregate on the surface of copper, Cu-Sn intermetallics are replaced by Cu-Al-Zn ternary intermetallics.A series of Cu-Al-Zn intermetallic layers with thickness of 1-5μm were obtained by changing brazing parameters. When the interfacial intermetallics were 2μm and 5μm thick, tensile stress of the joints was 65-70MPa. As it decreased to 1μm, the tensile stress was 75-80MPa.A new way to join copper and aluminum was proposed. Using ultrasonic aided plating technology, solders were plated on copper pieces before brazing, meanwhile, intermetallic layers formed between copper an solders were crushed into small pieces and scattered in solder, forming a depletion layer. This kind of structure was kept even after brazing. In this way, tensile strength of the joints was improved to 77-89MPa. A new way to enhance interfacial connection is discussed.