Optimizing the Strength and SCC Resistance of Aluminum Alloys used for Refurbishing Aging Aircraft

摘要

The focus of this report is on the mechanical end corrosion properties of high-strength aluminum alloys. Aluminum alloy 7075, a common material in the aerospace industry, is susceptible to stress-corrosion cracking (SCC) in the T6, or peak-aged temper. The susceptibility of this temper to SCC is alleviated through the use of the T73, or overaged temper. This temper exhibits significantly better SCC resistance, but at a 10-15% strength loss compared to the T6 temper. Cina end Ranish patented a new heat treatment known as retrogression end reaging (RRA) in 1974. Experimental test results indicate that the RRA heat treatment reduces the traditional trade-off between T6 strength end T73 SCC resistance. However, the short time heat treatment limits the applicability of REA to thin sections of material. The primary goal of this research was to determine if lower retrogression temperatures could be used in the REA process to extend the applicability of this heat treatment to thick sections. Tensile, fatigue, fracture toughness, and hardness tests were conducted to characterize the mechanical properties of the T6, T73, and various RRA tempers. Alternate immersion and double-cantilever beam tests were conducted to evaluate the corrosion properties of the different tempers.