The main problems with copper aluminum welding are corrosion and aging of the joints. Corrosion is caused by the electrode potential difference between aluminum and copper. During the welding process, copper aluminum brittle compounds are prone to occur in the weld seam. When the joint works in a high-temperature environment for a long time and is subjected to mechanical vibration, it can also cause the diffusion of copper aluminum atoms to form an intermetallic compound layer and continuously thicken it, resulting in a decrease in the impact toughness of the joint and an increase in resistance. During copper aluminum brazing, the use of highly corrosive fluxes to remove dense aluminum oxide films also results in the problem of flux residue corroding the joint.
In order to minimize corrosion and aging, the industry has adopted various welding methods such as pressure welding, melting welding, and brazing from different perspectives such as process and materials.
One of the more promising methods is the brazing process of coating Ni metal layer. The atomic diffusion barrier effect of Ni layer has been confirmed and widely applied. In copper aluminum brazing process, the use of Ni layer can not only avoid direct contact between copper and aluminum atoms, but also more effectively prevent mutual contact caused by diffusion of copper and aluminum atoms, thereby ensuring high strength.
If a layer of metal with good bonding and excellent brazing properties is plated on top of the Ni layer, no gas protection is required, only non corrosive or low corrosive fluxes can be used, thus solving the problem of corrosion resistance and simplifying the process.
Because copper and aluminum are both easily oxidizable metals, copper aluminum welding has always been an international welding challenge. Research in this area will help to obtain satisfactory copper aluminum joints and promote the widespread application of aluminum copper joints in industry.
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