Effect of Hexavalent Chromium Content on Performance of Chromate Films

摘要

An analytical method, developed to determine relative amounts of Cr (6+) and Cr (3+) in a chromate film makes possible correlative studies of chromium content and film properties such as salt spray life, electrical resistance, and paint adhesion. For the proprietary film studied, salt spray life and electrical resistance increase with increasing soluble Cr (6+) content. Removing the Cr (6+) by bleaching or rendering it insoluble by heating, decreases salt spray life and electrical resistance. The salt spray life of a bleached film which has been heated is approximately the same as that of a bleached film which has not been heated. The effect of chromium content and chromium species on paint adhesion is not clear cut as yet. These preliminary tests indicate pretreatment to be of more significance. (Author)