Anticorrosion mechanisms of aluminized steel for hot stamping

An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compared to untreated 22MnB5 steel is observed in cyclic corrosion tests even though cracks are present in the coating after the hot stamping resulting in the simultaneous corrosion of the coating and the steel beneath. The coating shows a poorer performance in continuous salt spray test than in cyclic corrosion test. Electrochemical measurements and in situ measurement of the elemental dissolution rates combined with the characterization of the corroded surface are used to argue in favor of an anticorrosion mechanism related to the barrier protection by corrosion products formed. Al and Fe oxides were formed in continuous test and aluminosilicates and a mixture of hydroxides after the cyclic test. The formation of specific corrosion products is assumed to be due to a specific surface pH evolution during corrosion testing.