Improvement in the Brazeability of Aluminum Clad Thinner Fin for Automotive Heat Exchanger

Through the years, aluminum automotive heat exchangers have been developed in order to have a high performance and a light weight. Therefore, the thickness of the aluminum sheets for the application has been reduced. As the brazeability declines with the reduction in thickness, fins having a thickness under 80μm may be difficult to secure a good brazeability. Therefore, we studied the brazeability to determine the limit of thickness using clad fins from 40 to 80μm. The fillet volume formed at the joints of the fin and tube decreased with the decreasing fin thickness and the Si content in both the filler metals and the core alloys. The suitable range of Si content in the filler metals and the core alloys to obtain a good brazeability decreased with the decreasing fin thickness. When the fins were thinner than the critical values, it was impossible to have a good brazeability. It was found that molten filler alloy was reduced by diffusion into the core during the heat up process before reaching the melting point of the filler alloy. Our results indicated that it was possible to obtain a good brazeability using the rapid heating cycles for brazing, even when the thickness was 40μm.