heat exchanger, brazing, material compatibility
Aluminum is one of the most commonly used metals for manufacturing heat exchanger. Mass production of compact aluminum heat exchangers can be achieved by furnace or flame brazing with the assistance of fluxes. It is well known that a brazing process relies on the capillary flow of liquid filler metal on the base surfaces of various heat exchanger components. Proper selection of heater exchanger materials is essential for the success of a brazing process. For example, the 6xxx series aluminum alloys are a popular selection in production processes due to their excellent mechanical strength and good machinability. However, the high percentage of Mg content in this alloy category makes it difficult to braze these alloys by CAB furnace processes. On the other hand, the 3xxx series aluminum alloys with Mn as major alloying element are suitable candidates for CAB brazed aluminum heat exchangers because of the excellent wettability of Al based filler metal when assisted by fluxes. In this study, selected commercially available aluminum alloys are used for wettability tests by Al based filler metals under CAB brazing condition. During the manufacturing or installation processes of the aluminum heat exchangers, there is often the need to join components that are made of dissimilar metals, such as Al/Cu joints and Al/stainless steel joints. Therefore, wetting behaviors of selected filler metals on commonly used Cu and/or SS surfaces are investigated as well. The phenomena closely related to liquid filler metal wetting behaviors on base metal with different material compositions are studied using sophisticated visualization tools and facilities such as heating stage and transparent furnace. Metallurgical cross section samples are prepared and examined using optical microscope to study the interactions between filler and base metals.