摘要：For the purpose of applying hot-dip Zn-6%Al-3%Mg alloy coated steel sheet (“Zn-Al-Mg”) to automotive parts, we compared and investigated the corrosion resistance of Zn- Al-Mg and ordinary materials treated using a conventional rustproofing method (“post-Zn-coated material”) exposed to accelerated corrosion test environments. We also collected automotive parts made from Zn-Al-Mg from vehicles that had been driven for three to five years in Canada to examine corrosion resistance capabilities when exposed to actual vehicle environment conditions. We found that Zn-Al-Mg exhibited better corrosion resistance than post-Zn-coated material, even at portions where the steel substrate was exposed (along cut edges and in bent or spot-welded portions). Such Portions of the Zn-Al-Mg were observed as being covered by fine and dense Zn corrosion products containing Mg, which suppresses cathode reactions (dissolved oxygen reduction reactions). As a result, elution of the coating layer around such portions was suppressed and favorable corrosion resistance maintained. The flat and bent portions of automotive parts made of Zn-Al-Mg collected from actual vehicles were covered by fine and smooth corrosion products, with only little corrosion being observed. It was thus confirmed that Zn-Al-Mg also exhibits excellent corrosion resistance in an actual vehicle environment.
