Evaluation of the pitting corrosion for aluminum alloys 7020 in 3.5% NaCl solution with range of temperature (100-500) °C

Abstract

The effect of homogenous heating variables (temperature and time holding) on the tendency of high strength Al-alloys type 7020 is investigated. The experiments were carried out by heating the specimens at different temperatures (100, 150, 200, 250, 300, 350, 400, 450 and 500) °C for two periods of holding time (one hour and two hours). Microstructure of an alloy was investigated by the optical microscope before and after heating at each temperature and precipitation phase and clearing revealed MgZn2. An immersion test was applied on specimens after heating to show the reduction in weight. Polarization technique was used to study the effects of microstructures on their electrochemical behavior in 3.5% NaCl solution. Microscopic and X-ray examination were used to reveal pitting corrosion on the microstructure of non-heated and heated 7020 Al-alloys. The results show that increasing the temperatures of heating from 100°C to 500°C caused the appearance of pitting corrosion on the precipitated phases and increase of pitting corrosion tendency with increase of temperature of heating; increasing time holding of heating from 1 hr. to 2 hrs. increases the pitting corrosion.