Copper and brass radiators have served the automobile industry for many years using traditional fabrication processes. Demand for newer and stronger radiators with lighter weight for the modern vehicles prompted investigation of alternate materials. Properties of zinc alloys and their compatibility with brass suggested these could be used for radiator manufacture.
Many zinc alloy compositions were investigated in the initial studies, because a solder alloy has to have many positive attributes. The first screening studies evaluated the ability of the solder to spread over copper and brass surfaces, representing tube, fin, and header materials. The second most important feature was the melting range of the developed alloy. In order to retain the anneal resistance of the fin and temper in the tube it was desirable to have a zinc solder with a melting temperature at 800°F or less. Metallurgical compatibility with the copper materials was investigated followed by joint strength testing at room and radiator operating temperatures. Corrosion resistance to ethylene glycol engine coolants and road salt environments was investigated to develop zinc solders with sufficient corrosion protection in addition to manufacturing benefits.
The new zinc solder joining system provides better thermal conductivity at the critical tube to fin joint. Zinc solders sustain their strength up to 300°F. Radiators made with the material do not have any strength reduction at automobile operating temperatures. The zinc solder material is also lighter, reducing average radiator weight by approximately one pound.
These characteristics made the development program for a practical manufacturing system a worthwhile proposition.
This paper includes work on development of the zinc solders, fluxes, and joining methods. Radiator tube manufacture is described and a new core bake furnace introduced that is capable of rapid tube joining. Prototype radiators have been made with manual joining of the tube to header joints. Service durability is under investigation by simulated vehicle service testing. Internal and external corrosion studies have demonstrated that zinc soldered radiators will have a longer life than current lead tin joined copper brass radiators.