Correlation between mechanical properties and corrosion behavior of an Al 6061 alloy coated by 5% CH3COOH pressurized steam and RRA heat treated

In this work, aluminium 6061 alloy samples were subjected to a 5% CH3COOH pressurized oxidizing steam process and to sequential heat treatments. The heat treatments effect on the ultimate tensile strength UTS, yield strength YS, and its correlation with the corrosion current density icorr and the corrosion potential Ecorr, along with the coating formed on the alloy surface were characterized. Empirical equations were developed in order to describe the behavior and correlation among the process parameters on the YS, UTS, icorr and Ecorr. The X-ray diffraction XRD and the Energy Dispersive Spectroscopy EDS were used to characterize the chemical composition of the oxide layer formed after the oxidizing steam process and the designed heat treatments. Chemical reactions were proposed following the EDS results and the reactants (alloy and steam), finding the formation of aluminium carbonate Al2(CO3)3, which is unstable and decomposes in α − Al2O3 alumina as the main phase, and the potential formation of a periclase oxide type (MgO) and a spinel oxide type (MgAl2O4) as the trailing phases, deposited on the material surface. According to the potentiodynamic polarization test results, the coated samples subjected to ageing (200 °C)-retrogression (250 °C)-reageing (150 °C) heat treatment showed an enhancement on its corrosion resistance without significant losses in the mechanical properties, when compared to the aluminium 6061-T6 alloy condition.