A class of corrosion-resistant brazing sheet materials, generally referred to as “long-life alloys,” has been in widespread use in brazed aluminum automobile radiators for over ten years. “K319” tube material was initially introduced in 1986 to address the problem of road-salt-induced, outside-in corrosion of tubes in vacuum-brazed aluminum radiators. The
development history, metallurgy, and field performance of long-life radiator brazing sheet are reviewed. This material utilizes the familiar sacrificial layer concept to improve corrosion resistance; however, it is unusual in that the layer is not introduced by conventional cladding means during sheet manufacture, but rather develops in situ by
metallurgical transformations which occur during the brazing cycle. The sacrificial layer, about 25 mV anodic to the core alloy, increases by an order of magnitude the time-to-perforation of radiator tube sheet tested in cyclic acidified salt spray (SWAAT), which mimics the corrosion morphology observed in the field. Radiators examined after ten years of field service show excellent corrosion resistance, as predicted by SWAAT.
Keywords: brazing sheet, aluminum radiators, vacuum brazing, road salt corrosion, long-life alloys, field retrievals, SWAAT