Universal chromic acid anodizing method

摘要

What is disclosed is an improvement in a method of anodizing aluminum alloy parts to meet predetermined specifications regarding salt spray corrosion resistance, fatigue failure resistance, paint adhesion and coating weights and including the steps of connecting the aluminum alloy parts to an anode of a direct current voltage source that is positive with respect to a cathode, immersing the aluminum part near the immersed cathode in an electrolyte comprising an aqueous solution of chromic acid; and carrying out the anodizing under a predetermined voltage differential for a predetermined time with the electrolyte at a predetermined temperature. The improvement comprises employing a differential voltage in the range of 15-25 volts direct current between the anode and cathode, maintaining the temperature of the electrolyte in the range of 85 DEG F.-110 DEG F. and carrying out the anodizing for a time interval in the range of 20-60 minutes. In a preferred embodiment, the anodized aluminum parts are given a seal commensurate with the paint adhesion characteristic desired. For example, if a lesser degree of paint adhesion is desired, a hot water seal is employed; whereas if a higher degree of paint adhesion is desired a sodium dichromate seal is employed, or given the anodized aluminum part.