Effects of Quenching on Corrosion and Hardness of Aluminum Alloy 7075-T6

Quenching affects the mechanical and corrosion properties of precipitation-hardenable alloys such as aluminum alloy 7075-T6 (AA7075-T6). In this paper, the properties of as-quenched AA7075-T6 are predicted within the framework of quench factor analysis (QFA), using cooling curves obtained from a quench test. Theoretical and computational approaches are used to predict spatial and temporal variations of temperature. The temperature variations are used to predict the quench factor and consequently the material properties. A test is carried out on a block of AA7075-T6 quenched partly in water and partly in air followed by hardness measurements and electrochemical characterizations. The results show that the hardness and the corrosion potential of the quenched block decrease as the cooling rate decreases. The results further suggest the existence of a corrosion product layer for the water-quenched part of the sample. This was not observed for the air-cooled part. A new corrosion prediction model is developed by using the QFA method, cyclic polarization, and electrochemical impedance spectroscopy test results. The present model may be used to potentially reduce the number of corrosion tests in evaluating corrosion properties of quenched AA7075-T6. Model predictions for corrosion and hardness are in good agreement with experimental results.