Development of Quad-layer Clad Brazing Sheet for Drawn Cup Type Evaporators: Part 1 2001-01-1253

Having a light weight, a good heat conductivity and a good brazability, aluminum alloy is widely used for automotive heat exchanger systems. The major problem with Aluminum is perforation of the tube by pitting corrosion and corrosion protection is necessary in the field. In radiator and condenser systems using the the Nocolok brazing process given good corrosion resistance using cathodic protection with sacrificial anode made of Zn-sprayed onto tube or low corrosion potential fins etc. On the other hand, in drawn-cup type evaporators, that are fabricated from brazing sheet tubes in vacuum brazing method and then covered low electro-conductive drain water film in operation, the effect of cathodic protection by the anode fin is limited to a very small area. Therefore, this has been studied to improve self-corrosion resistance of the core in the brazing sheet tube.

As the results of these problems, tube thickness of a drawn cup evaporator been remained from two to three times thicker than that of a radiator and a condenser. In order to achieve downsizing of a drawn cup evaporator, the quad-layer brazing sheet tube, that has a sacrificial anode layer between an out-side solder layer and a core layer was studied. This paper describes the basic study of the material development and the next paper describes its actual use. Using some accelerated corrosion tests, the quad-layer brazing sheet tube had successful corrosion resistance. Besides the corrosion tests, basic electrochemical measurements and galvanic coupled corrosion tests were carried out as well. These results suggested that the balance of corrosion potential among core alloy, sacrificial anode alloy and outer solder alloy was important to get good cathodic protection effect for the longest duration.