Study of the influence of the RRA thermal treatment and plasma nitriding on corrosion behavior of 7075-T6 aluminum alloy

Abstract

Aluminum alloys are mainly used in aircraft's structural components, which present the fatigue process as a predominant failure mode. The fact that there are many airports in coastal regions makes the study of aluminum alloy corrosive processes relevant as localized corrosion causes adverse effects on mechanical properties of the material. Plasma nitriding is an alternative method of raising surface hardness, fatigue resistance, wear and corrosion of alloys, there is a trend to expand the applicability of the plasma nitriding process through utilization of new materials and nitriding of aluminum and its alloys would be of greatest interest. In order to improve the corrosion behavior of 7075-T6 aluminum alloy, this work evaluated and compared the effect of RRA thermal treatment and plasma nitriding on the corrosion behavior of AA7075-T6 alloy. The tests were performed in 3.5%wt NaCl solution at room temperature (~25 °C) and pH ~ 6. The linear potentiodynamic polarization study showed that RRA thermal treatment and plasma nitriding were effective in improving corrosion behavior in saline solution. The protective efficiency of plasma nitriding was 64.2% and RRA treatment was 18.4%. The corrosive process at the T6 condition was deeper and generalized, with a high concentration of corrosion pits. For the RRA condition, the process was less generalized and not so deep, while in the plasma nitrided condition it was more localized and superficial, preserving much of the exposed surface in the corrosion tests. These results can be considered very promising by indicating an increase in the useful life of this material. This directly implies a consequent reduction in the preventive maintenance costs of the industries that use this alloy, as replacing damaged parts that have been treated by the plasma assisted technique used in this study may be performed at longer time intervals than the alloy parts without any kind of treatment.