Correlation between Accelerated Laboratory Tests and Field Tests for Filiform Corrosion of Painted Aluminum Alloy Sheets for Automobiles

Correlation between accelerated laboratory tests and field tests for filiform corrosion of painted aluminum alloy sheets for automobile was investigated by conducting six kinds of laboratory tests with different pH, dry-wet condition, etc., and two sites of outdoor exposure tests, and vehicle test. It was found that susceptibility to filiform corrosion in the laboratory tests increased with the decrease of pH and/or the increase of repetition rate of wet/dry cycle. The susceptibility in the laboratory tests also increased with the increase of Cu contents in the alloy or with the sanding treatment before painting. The same tendency was obtained in the outdoor exposure tests and vehicle test. However, the correlation of the outdoor exposure tests and the vehicle test was low. In conclusion, the laboratory tests with relatively low wet ratio (70%) correlated well with the outdoor exposure tests, and the tests with relatively high wet ratio (95%) correlated well the vehicle tests.