Although it requires practice, brazing of aluminum to copper can be successful using a tightly controlled process. The most appropriate technique to use when joining these two base metals is flame brazing, using a low-temperature melting flux and brazing alloy. While the process of brazing aluminum to copper is similar in nature to the process of brazing aluminum to aluminum, certain steps must be taken to insure a quality braze joint.
One of the most common braze failure issues when joining aluminum to copper is related to heating the joint. If improper technique is used and heating takes too long, excessive diffusion will occur at the braze joint. Excessive time at the brazing temperature may also compromise corrosion resistance due to metallurgical changes. It is important to use good braze technique, applying heat adjacent to the joint rather than on the joint itself, allowing heat transfer by conduction, and removing the flame as soon as the filler metal reaches a liquidus state.
Equally important to keep in mind when brazing aluminum to copper is the different melting points of each of the base metals. While copper melts at 1984˚, aluminum melts at 1220˚ and as such, flame should be directed onto the copper. However, once heat transfer from the copper to aluminum allows the aluminum to reach 1220˚, the aluminum will very quickly reach the flow temperature. This process is complicated by the continued absorption of heat by the copper and its subsequent transfer to the aluminum; therefore it is recommended that the flame be removed from the copper as soon as the aluminum begins to melt. Overheating of the aluminum will cause alteration of its metallurgical properties.
Aluminum to copper brazing is used by many companies for large scale production. Bellman-Melcor offers a variety of ChannelFlux alloys to help meet the needs of customers brazing aluminum. ChannelFlux provides an ideal design and chemical composition for the easy brazing of aluminum to copper. Call for a quote or with technical brazing questions today!