1. ABSTRACTThe use of low-density materials in body panels is increasing as a measure to reduce the weight of the vehicle body. Honda has developed an aluminum/steel sheet hybrid door that is more effective in reducing weight than an all-aluminum door. Because aluminum was used in the door skin, bimetallic corrosion at the connection between the aluminum and the steel sheets represented an issue. It was possible that the difference in the electrical potential of the two metals might promote corrosion at the connection between the aluminum door skin and the steel sheet door panel, in particular at the lower edge of the door, where rainwater and other moisture tends to accumulate, with the result that the appeal of the exterior of the door might decline. To address this issue, a watertight structure realized through the use of a high-ductility sealer was employed in order to help prevent water from infiltrating to the connection between the metals, and steel sheets with a zinc-aluminum-magnesium alloy coating, highly effective in controlling bimetallic corrosion, were employed in the door panels. This produced rust-resistance specifications for the hybrid door able to maintain durability in market use environments. This paper discusses the effect of the zinc-aluminum-magnesium alloy-coated steel sheets in controlling bimetallic corrosion.