Corrosion Testing of an Al-Zn-Mg-Cu Alloy After Different Heat Treatment Regimes by the Application of Electrochemical Methods

Abstract

Abstract: The corrosion tendency in the 7000 series aluminium alloys changes depending on the content of alloying elements, thermal and thermo-mechanical treatments, etc. An alloy of this type applied in the production of weapons and military equipment has been investigated by applying different electrochemical methods. A degree of the precipitation hardening (aging) of the alloy has been evaluated by measuring its electrical resistivity. The corrosion potential measurements (Ecorr.) gave information about the distribution of the alloying elements between the solid solution and the precipitation phases. The polarization measurements, performed in the 0.5 M NaCl solution, have shown a more positive value of the pitting potential (Epit.) and a greater corrosion resistance for the two-step aged alloy. The electrochemical impedance spectroscopy (EIS) has also shown that the two-step aged alloy has better corrosion properties (a higher value of polarization resistance, Rp, and a lower value of capacitance, Cdl) comparing to the one-step aged alloy. These results enable a deeper insight into the effects of both heat treatment and alloying elements, primarily copper, on the corrosion resistance of the tested alloy.