Techniques for Improved Surface Integrity of Aerospace Aluminum Alloys
The optimum performance of aerospace components and structures usually depends on the achievement of high strength, high fatigue resistance and resistance to many forms of surface degradation including wear, fretting, corrosion and stress corrosion cracking. In the case of high strength aluminum alloys, trade-offs are often made between strength and corrosion resistance, such as those brought about by standard heat treatments T651 or T7351. The Retrogression and Re aging Process, first described by Cina et al. has shown that near surface properties can be modified by novel heat treatment procedures to obtain strength levels equivalent to the T651 temper together with stress corrosion resistance equivalent to that of the T7351 temper. This success has stimulated other work to investigate derivative heat treatments that might provide similar benefits in thick section parts. This paper reviews these new approaches to heat treatment and provides examples of the effects of these treatments on the properties of thick section parts with major dimensions up to 76 mm. The effects of processing on the microstructure conductivity, resistivity, yield strength, hardness, fatigue, corrosion fatigue and stress corrosion cracking of typical 7000 series alloys are described.
KeywordsCrack Growth Rate Stress Corrosion Crack Closure Fatigue Crack Growth Rate Corrosion Fatigue
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