Variation of thickness of hard anodic films

An investigation was made of the effects of varying processing conditions on the thickness of anodic films produced by the Martin Hard Coat (4) process on commercially pure aluminum and nine aluminum alloys. This study was conducted to provide sufficient data for designing coating thicknesses on aircraft accessory parts that would conform to the close tolerances maintained in the course of manufacture of precision components. Coating thicknesses up to 0.0051 in. were obtained. Changes in electrolyte strength, temperature of the bath, alloy composition, and current density were made to see their effect on the thickness of the film and growth of the part. The first three aforementioned variables caused slight variations in the film thickness. Current density was the chief determinant of the thickness of the hard coat film. Growth of the part was only affected slightly by changes in processing conditions. The growth of the part averaged 0.41 of the over-all film thickness. Coating ratios increased with time of film formation; higher coating ratios were obtained with low strength electrolytes, low bath temperatures, and high current densities