Statistical Analysis of Corrosion Current Density and Tensile Strength of Al-6061 Alloy by Ageing and Retrogression Heat Treatments

In this work, the effect of ageing and retrogression on the polarization resistance of the Al 6061 was assessed, in order to improve the corrosion resistance of the alloy with a negligible effect on the tensile strength. The corrosion resistance behavior was studied by exposing an Al 6061 alloy to a simulated marine environment, and then, the corrosion current density (icorr) was measured. The obtained corrosion results were correlated with tensile strength (TS) reported elsewhere and both measured, the icorr and TS and both were modeled by multiple linear regression. The results showed that the polarization resistance is inversely proportional to the temperature increment of the ageing and retrogression processes. In addition, the samples subjected to 200 °C of ageing and 250 °C of retrogression temperatures exhibited an enhancement on both corrosion resistance and tensile strength, when compared to the T6 condition and to lower ageing and retrogression temperatures. Furthermore, an empirical equation was proposed to correlate the icorr as a function of heat treatment parameters such as: ageing temperature and retrogression time–temperature for the aluminium alloy.