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In order to clarify the effect of design and materials of the hem as well as the climatic factors on perforation corrosion of the automobile doors, field car and laboratory investigation has been carried out Field car investigation revealed that corrosion of the hem can be minimized by using two side galvanized steel plus adhesives. The ratio of wet/dry environment was evaluated in laboratory on hemmed sample, and it was found that the design of the hem in conjunction with the various wet/dry ratio affected the corrosion rate differently.

Three doors from three field vehicles made with one-side galvanized steel on the inside of the outer panels were investigated for perforation corrosion using microscopic and analytical methods after 8 or 10 years' field exposure in the snow-belt areas of North America. Perforation of these doors occurred within the lapped part of the door hems. Outer panel perforation began at the zinc layer on the inside surface of the outer panel at the lapped part and/or at the “bent part” of the outer panel of the door hems. Details of the micro corrosion behavior for the inside surface of the outer panel were made clear using EPMA analyses. The corrosion products on the inside surface of the outer panel were identified with X-ray diffraction. Initially, zinc corrosion begins at the zinc coating layer of the upper side at the wax-free zone of the lapped part.