Elevated Temperature Aging of 24S Aluminum Alloy

Abstract

The aging of strong aluminum alloys at elevated temperatures is not a new process and the attainable physical properties have been studied for a number of the alloys used in aircraft construction. However, the fear of corrosion difficulties and the lack of detailed information regarding the physical properties obtainable and the optimum conditions of time and temperature required to attain these desired properties for 24S alloy have delayed the application of this process in aircraft fabrication up to this time. Various combinations of time and temperature will produce similar results, but the most satisfactory treatment for 24S aluminum alloy appears to be at 375 °F. for 8 hours. This treatment will raise the tension yield point of the material approximately 50 per cent and the ultimate tensile strength about 10 per cent, while at the same time the elongation is reduced to approximately 5 per cent in 2 in. In general, after aging treatments, the physical properties in compression are slightly lower than in tension. The corrosion resistance of aluminum-coated sheet is not seriously impaired but that of bare 24S alloy is appreciably lowered. Elevated temperature aging of bare 24S in thicknesses below 3 / i6 in. is not advisable because of the increased tendency for inter crystalline corrosion. The maximum physical properties obtainable by aging with any combination of time and temperature are largely dependent on the elastic strain present as a result of cold-work performed after the solution heat-treatment and before the elevated temperature aging. In order to assure consistent physical properties after an elevated temperature aging has been performed, it is necessary to control the degree of cold-working which the material undergoes during its manufacture.