An Investigation Of The Effect Of Retrogression And Reaging (RRA) Treatment On Stress Corrosion Cracking (SCC) Of Aluminum Alloy 7075

Nurul Mardhiah, Mohd Azizuddin (2010) An Investigation Of The Effect Of Retrogression And Reaging (RRA) Treatment On Stress Corrosion Cracking (SCC) Of Aluminum Alloy 7075. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

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. Retrogression and Reaging (RRA) is a new thermal process introduced for the purpose of enhancing corrosion resistance of 7075-T651 aluminum alloy while maintaining its T6 strength. In this study a 7075 material so treated was investigated for its mechanical and corrosion resistant properties. Results indicated that the RRA treated 7075 was significantly better than the T6 temper in resistance to stress corrosion cracking and exfoliation corrosion. The loss in strength from RRA treatment was minimal. Electron microscopy of the fractured surface showed a distinct difference in the fracture mode when compared to the T6 temper condition. Tests results indicated that the RRA heat treatment resulted in fatigue and fracture toughness properties superior to the 7075-T651.

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