Application of zinc alloy coated steel sheets as the substrates of weldable prepainted steel sheets has been investigated.
As zinc-nickel alloy coating improves corrosion resistance of the weldable prepainted steel sheets to agreat extent, thickness of electrically conductive paint film is able to be reduced to 5 μm. This results in improvement in their weldability and formability. The zinc alloy coating containing iron more than 9wt% is apt to form red rust.
Based upon above results, the surface coated steel sheet having 5 μm of electrically conductive paint film containing totally 30 vol% of zinc, stainless steel and aluminium powders upon 10 g/m2 of zinc-nickel-chromium-iron alloy coating has been developed. This product is much superior in press formability, weldability and corrosion resistance to zincrometal and has been put into practical use in the automotive industries.
