Surface defects in car paint from recombination of atomic hydrogen

Car-body sheet was corrosion protected by galvanic zinc coating, followed by several corrosion protective layers and paints and finally baked at elevated temperature to harden the paint. Point defects were observed on the outer and inner surfaces of a bonnet after finishing of the painting process. Metallographic examination of cross sections of defects showed that the defects were craters, which spread through all protective layers. The bottom of the crater was connected with a crack in the zinc layer. The main reason for the defects was gas from the galvanic zinc coated sheet.