Role of pre-strain on the corrosion behaviour of Al-Zn-Mg P/M alloy

Abstract

In the present study, Al-Zn-Mg alloy has been fabricated through the powder metallurgy route by keeping Zn content at 5.6% and varying Mg from 0% to 3%. The optimum composition of Mg was found to be 2% based on relative density, microhardness and microstructure. Al-5.6Zn-2Mg was subjected to deformation at various temperatures (300 ^°C, 400^°C and 500^°C) and strain rates (0.5, 0.05 and 0.005). Potentiodynamic polarization and electrochemical impedance spectroscopy were used to assess the electrochemical behaviour of deformed preforms. Scanning electron microscopy was utilized to study the microstructure and corrosion morphology of Al-5.6Zn-2Mg under different conditions. In the present study, deformation behaviour (axial strain (ε_z), formability stress index (β_σ)) has been related to mechanical (hardness) and electrochemical properties (corrosion rate, pitting potential (E_pit)). By increasing deformation, potentiodynamic polarization results showed a decrease in corrosion current density (i_corr) and an increase in pitting potential, which increased the corrosion resistance of the alloy. The corrosion resistance of the alloy increased significantly by increasing deformation temperature and lowering strain rate. Corrosion rate also decreases with an increase in axial strain and formability stress index. The corrosion mechanisms found in deformed preforms were pitting and intergranular corrosion. The corrosion morphologies also revealed the closure of pores due to increase in temperature and a decrease in strain rate.