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As a demand for vehicles of higher functionality grows, automakers and material suppliers are devoting increasing efforts to develop technologies for greater safety, lighter weight, higher corrosion resistance, and enhanced quietness. The resin-sandwiched vibration damping steel sheet (VDSS), developed as a highly functional material for reducing vehicle vibration and noise, has been used for oil pans1) and compartment partitions2). First applied for a structural dash panel of the new Mazda 929, a Zn-Ni electroplated VDSS which allows direct electric welding has contributed to greater weight reduction as well as improved quietness.

Research work was conducted on the development of two-layer coated steel sheet, a new corrosion-resistant material based on galvannealed steel that can be used in automotive outer panels and can be easily produced to a heavy coating weight as long-life corrosion-resistant steel and electroplated with an iron-rich iron-zinc alloy. As a result, the two-layer coated steel with a 30 g/m2 galvannealed coating + 3 g/m2iron-zinc alloy electroplated coating on the exterior surface and a 60 g/m2 galvannealed coating on the interior surface was found to be excellent in electrodeposited primer film cratering resistance, wet adhesion and blister resistance, to last long against scab corrosion and perforative corrosion, and to have good press formability and weldability. The method employed for electroplating the iron-rich iron-zinc alloy on the galvannealed coating is also described.