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Aluminum Tech Talk: Stress Corrosion Cracking Resistance of Peak Aged Al-Zn-Mg-Cu Alloy

Aluminum Tech Talk 

Stress Corrosion Cracking Resistance of Peak Aged Al-Zn-Mg-Cu Alloy

The project was aimed at evaluating and improving the stress corrosion cracking (SCC) resistance of forged AA7010 alloy. A forged block of dimensions (550x150x100) mm was subjected to different heat treatment processes and the response to SCC resistance was compared and studied. Standard round SCC samples were machined from blocks of (70x10x25) mm cut off from the original block where the tensile axis was along short transverse direction for the first batch and along longitudinal direction for the second batch. An attempt was made to study the effect of SCC in both the directions of the forged alloy to compare and explore ways to mitigate SCC by thermal treatments. Optical and Scanning Electron Microscopy was used to study initiation and propagation of SCC, crack morphology and other physical properties of forged and heat-treated AA7010 alloy subjected to ASTM G44 and ASTM G47/79 tests. Crack initiation and  propagation in inter-granular mode  were related to various models proposed in the literature. The crack initiation mechanism started at the corrosion pits with propagation mechanism being attributed to the tarnish rupture model and also crack propagation due to wedging. It was concluded that the alloy in short transverse direction is more susceptible to stress corrosion cracking than in the longitudinal direction after forging. Retrogression and re-aging treatments when compared to T6 and T7 tempers improved the stress corrosion cracking resistance of the alloy.

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June 9, 2014 - Posted by | Blog Posts

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