A major program was launched by Ford Motor Company in 1976 to develop lightweight and durable aluminum heat exchangers. This program resulted in the identification of two radiator designs: a brazed flat tube design for maximum efficiency and weight savings and a mechanically assembled design with superior mechanical durability at a reduced facilities investment. Both designs have plastic tanks mechanically crimped to the header and an epoxy coating added to the air side of the header to insure mechanical integrity and leak-free tube-to-header joints.
Heat exchanger development testing of both brazed and mechanically assembled aluminum radiators ranged from simple laboratory glassware tests to controlled fleet and limited production field tests. A key element of this development program was the tracking and retrieval of radiators from two large-scale field trials. Radiators from these trials were analyzed metallographically for internal and external corrosion. Only 3 of 150 mechanically assembled aluminum radiators analyzed showed significant corrosion. For these three samples, high chloride levels (>100 ppm), low glycol concentrations (<30%), and very low inhibitor levels were found. Significant internal corrosion in prototype vacuum brazed aluminum radiators was found to be related to tubes clad with AA7072 and the use of a AA6951 header material. Subsequent production level radiators with no sacrificial clad on the tube interior surfaces and a AA3005 header material showed very little corrosion. External corrosion was noted on tube surfaces for some vacuum brazed radiators retrieved from areas near the seacoast or where large amounts of deicing salts are used.
In general, projections made on the basis of the retrieval studies indicated that the aluminum radiators have comparable or better durability than current production copper/brass radiators. Copper/brass radiators appear to be more susceptible to field performance degradation because of external fin-to-tube solder corrosion after several years in service. Although material and design improvements have led to a marked improvement in the corrosion resistance of both copper/brass and aluminum radiators, further effort is required to attain a “corrosion proof” system. Current investigations involve improving clad/core alloys, external coatings, gasket materials, header designs, and braze processes.