Preferred Brazing and Soldering Conditions for Copper to Aluminum Transition Joints

As the global market for HVAC products continues to expand its use of aluminum components, the need for a suitable means of joining copper to aluminum has become apparent.  Manufacturers who are evaluating the use of aluminum components, such as evaporator and condenser coils, need to determine the best method of joining these aluminum coils to secondary copper lines or assemblies. Several joining means are used in industry for joining copper to aluminum including adhesives, mechanical joining, ultrasonic joining, soldering, and brazing.  When brazing or soldering is selected, several parameters need to be controlled to ensure proper joint integrity.  These parameters include the joint design (i.e. joint gap, shear depth, and Cu to Al orientation) and the brazing or soldering consumables (i.e. alloy and flux) that are selected.  Industry standards for these constraints are not currently available and recommendations on this topic vary from manufacturer to manufacturer.

In order to provide direction on what are preferred brazing/soldering conditions for joining of aluminum to copper, tests have been performed investigating the effect different joint designs and types of brazing/soldering consumables have on the overall quality of a copper to aluminum transition joint.  A series of specimens with varying joints gaps and copper to aluminum orientations were torch brazed/soldered with Al/Si and Zn/Al alloy systems.  These specimens were then mechanically and pressure tested to determine the resulting quality of the joined assembly.  Metallurgical examination was also performed to characterize the braze/solder quality that was achieved for each family of joints. The results of these tests have been summarized and are presented in this paper to assist manufacturers in determining suitable means for joining their copper to aluminum components.