Aluminum radiator tubes must have several demanding properties to be successful including good heat transfer, high strength to withstand internal pressures, brazeability for attaching external fins and headers, corrosion resistance to cooling fluids, and long service life. Tubes having a wall thickness of approximately 320 microns (11.8 mils) must meet all these properties. A modified simulated service test (SST) of various aluminum radiator tube alloys was conducted to determine how well coolant-side alloys of eight different composite materials resisted corrosion. Both coupons and actual radiator tubes were used in these tests. Coolant-side alloys that were examined included 1145, low-copper 7072, low-iron 3003, 3003 plus zinc, and 3005. The results of these tests indicate that corrosion will tend to proceed laterally along the tube surface when it is anodic to the core alloy. A coolant-side alloy consisting of 3003 plus zinc exhibited advantages over 7072 because its pit density was lower. The role of microstructure in the corrosion behavior of composite brazing sheets is discussed.
Keywords: aluminum braze alloys, internal corrosion, Oyama water, ASTM water