This report describes the results of weathering tests on 34 wrought aluminum alloys exposed seven years at four ASTM sites in the United States. Also included, for comparison, are data on three additional aluminum alloys exposed six years at five sites in England. The British industrial atmosphere exposures at Sheffield and London were found to produce the most corrosion, particularly on the sheltered sides of these panels which were exposed at an angle of 30 deg from the horizontal. The self-limiting corrosion characteristics were observed on weather surfaces at all test sites in both countries. The test will be continued and again reported after twenty years, as was the case in a previous ASTM B-3 test (ASTM STP 175) on older aluminum alloys.

Atmospheric exposures of 18 to 39 months have been completed at seacoast and inland industrial locations to determine the resistance to exfoliation corrosion of specially heat-treated test panels of high-strength aluminum alloys. Two seacoast locations, one at Point Judith, Rhode Island, and another at Daytona Beach, Florida, were selected, together with an industrial location near Chicago, Illinois, to represent the relatively severe atmospheric conditions to which aluminum alloy aircraft structures are subjected in service. The purpose of these tests was to demonstrate the relationship of the performances in the accelerated exfoliation corrosion tests previously evaluated by this task group with those in relatively aggressive natural environments. The exfoliation performance is being evaluated on test panels heat treated to produce three different metallurgical structures that would be expected to provide a high, low, and medium resistance to exfoliation of both a 7075 alloy extrusion and a 7178 alloy rolled plate. Results obtained thus far are gratifying in that the atmospheric exposures are ranking the test materials in the same relative order as the new ASTM Standard Method of Test for Exfoliation Corrosion Susceptibility in 7XXX Series Copper Containing Aluminum Alloys (G 34-72, EXCO test). That is, the materials that showed either a high or a low resistance to exfoliation in the EXCO test also showed the same performance in the seacoast atmosphere, and that which showed an intermediate resistance in the EXCO test showed more spotty and a slower rate of exfoliation in the atmospheric exposures. Exfoliation of the most susceptible items initiated more rapidly (within five months) at the seacoast, but the exfoliation tended to be more uniform at the industrial site. Other factors such as the climatic conditions at the seacoast, location, and exposure position of the test panels are considered.

A task group sponsored jointly by The Aluminum Association and the ASTM has recommended a standard method of test for susceptibility to stress-corrosion cracking (SCC) of 7XXX aluminum alloy products (ASTM G 47-76). The proposed standard is a comprehensive method that specifies the corrosive environment and period of exposure, type of test specimen and method of loading, procedures for sampling various manufactured product forms, and guidelines for interpretation of test results. Final selection of test procedures was based on round robin tests performed in nine different laboratories and 3-year exposures to the atmosphere in both seacoast and inland industrial locations. A summary of test results is given to illustrate how the relative performance of three different tempers of 7075 alloy plate can be influenced by the choice of a test specimen, differences in the outdoor atmosphere, and interlaboratory variations in performing the standard 3.5 percent sodium chloride alternate immersion test.