Abstract
Al-Si alloys have been used as a brazing material for constructing the car radiator, and are however corroded greatly in aqueous solution containing chloride anion even at a low concentration. A new surface treatment against the pitting corrosion of the alloys has been developed. The treatment consists of two steps, where a specimen of Al-Si alloy is immersed in neutral aqueous solution of Na4SiO4 at 2.5gdm-3 concentration at 95°C for 30min and then immersed in neutral aqueous mixture of 0.05 moldm-3 MgSO4 and 0.005 moldm-3 NaHCO3 at 95°C for 30min. The Al-Si alloy after the treatment is covered with a compact hydrated oxide film about 2μm thick and its resistance against pitting corrosion is much improved.
