抄録
A new surface treatment has been examined to improve the corrosion resistance of aluminum alloys. In the treatment the alloys were immersed in aqueous solution composed of 0.01M LiNO3 and 0.005M NaHCO3 at 95°C for 30min. Preferable resistance of those alloys pretreated to pitting corrosion was elucidated by the polarization measurements in 0.01M NaCl solution and the measurements of the maximum depth of pits formed in aerated NaCl solution containing cupric ions. The SEM photographs showed uniform but porous film of 2-4μm thick formed on the alloy surface treated. The film was identified by the X-ray diffraction analysis to be a mixture of Al2(OH)6·H2O and LiOH·2Al(OH)3·nH2O. It raised the pitting potential and depress reduction of oxygen dissolved in solution, resulting in the improvement of corrosion resistance. The surface treatment of pure aluminum, A 3003, A 5052, and A 7072 was useful to prevent pitting corrosion in chloride solution, but was ineffective to BA 4045 because of difficult formation of uniform protective film on the eutectic silicon segregation.
