SOURCES OF VARIABILITY IN CATION ANALYSIS FOR A QUANTITATIVE EXFOLIATION CORROSION-RESISTANCE TEST

Exfoliation corrosion of some high-strength aluminum alloys results in delamination of the metal surface resulting in a reduction of mechani cal properties. The susceptibility is a strong function of the metallu rgical condition of the material. Artificial aging treatments leading to higher strengths generally lead to higher susceptibility to exfolia tion. The results of a new, quantitative test for exfoliation resistan ce based upon solution analysis of dissolution products are presented. Capillary electrophoresis (CE) has been used to quantify the Mg2+ and Zn2+ leached by 10 mM HCl from the thermal oxide of aluminum alloy AA 7075 artificially aged to different degrees. An empirical relationship was found between the ratio of Mg2+ to Zn2+ dissolved during the test and the susceptibility of material to exfoliation. The development of the test is discussed with a focus on an analysis of its reproducibil ity and sources of variance. The primary sources of variability were f ound to be spatial variations in the composition of the thermal oxide and inhomogeneities in the test solution.