Influence of Heat Treatment of A 3003 Alloy on Chemical Treatment with the Mixed Solution of MgSO₄ and NaHCO₃

Abstract

The effects of heat treatment of A 3003 on the pitting corrosion preventive film prepared by the chemical conversion with aqueous solution containing MgSO₄ and NaHCO₃ were investigated. Resistance of the chemical conversion film to pitting corrosion was evaluated by polarization mesurements in 0.01M NaCl and the mesurements of the maximum depth of pits formed in aerated NaCl solution containing cupric ions. When A3003 was quenched from 600°C, the SEM photographs showed the intermetallic compounds such as (Fe, Mn) Al₆ on the alloy surface was refined. As the result, porous film about 10μm thick deposited on the heat treated alloy surface by the chemical conversion treatment. It raised the pitting potential and depressed reduction of oxygen dissolved in solution, resulting in the improvement of pitting corrosion resistance.