HIGH TEMPERATURE HARD ANODIZING WITH TARTARIC ACID-OXALIC ACID-TRIETHANOLAMINE BATH.

Abstract

Tartaric acid does not produce uniform films on A6063 alloy (Al-Mg-Si). Uniform films are formed when oxalic acid is added to the tartaric acid bath, but hardness above Hv 400 cannot be obtained at a voltage below 100 V. When 1 mol dm** minus **3 tartaric acid-0. 4-0. 6 mol dm** minus **3 oxalic acid baths were adjusted with triethanolamine (0. 26-0. 54 mol dm** minus **3) to pH 1. 00 and 1. 25, crack-free films with hardness above Hv 430 were formed at 40 degree C in the range 65-85 V. The hardness of the film is independent of the anion content of the film, increasing with increase in the thickness of cell wall and lowering in porosity.