The effect of quench rate and overageing temper on the corrosion behaviour of AA7050

• We study effect of quench rate on corrosion behaviour in various over-aged alloys.
• Corrosion resistance keeps increase with ageing time if slowly quenched.
• Severe overageing will slightly reduce corrosion resistance if fast quenched.
• Quenching has a much higher effect on intergranular corrosion than overageing step.
• Copper content in precipitates is the most important factor for corrosion property.

The corrosion behaviour of AA7050 on different quench rates and ageing conditions has been studied using immersion tests and complementary techniques like SEM, TEM-EDS and Scanning Kelvin probe force microscopy. The results reveal that overageing temper can effectively reduce corrosion sensitivity caused by peak-ageing treatment. The comparison of corrosion resistance in the over-aged and severely over-aged alloys shows significant dependence of the changes in corrosion resistance with ageing time on quench rate. The results are discussed in terms of the changes in the composition and distribution of precipitates, width of precipitate-free zone and diffusivity of alloying elements.