Corrosion Resistance of Different Metallic Coatings on Press‐Hardened Steels for Automotive

Abstract

The corrosion resistance of laboratory press-hardened components in aluminized, galvanized or galvannealed boron steels was evaluated through VDA 621-415 cyclic test for the automotive industry. 22MnB5 uncoated steel for hot stamping and standard galvanized steel for cold forming were also included as references. Corrosion resistance after painting (cosmetic corrosion) was quantified by measuring the delamination of electro-deposited paint from scribed panels. The rusting on their edges was used for determining the cut-edge corrosion resistance. The corrosion resistance on unpainted deformed panels (perforating corrosion) was quantified by mass losses and pit depth measurements. Zinccoated boron steels were found to be more resistant to cosmetic corrosion than the other materials, and slightly more resistant to cut-edge corrosion than the aluminized one. Red rust apparition could not be avoided due to the high iron content in all these hot-stamped coatings. The three coated boron steels showed similar performances in terms of resistance to perforation. Aluminized boron steel presents the advantage of being less sensitive to hot-stamping process deviation. Its robustness has been proved for many years on cars.

Surface and Coating Analysis of Press‐Hardened Hot‐Dip Galvanized Steel Sheet

“…All in all hot dipped galvanized steel sheet has a much higher corrosion resistance after press hardening and the generated coating is still able to offer protection for the steel substrate according to the cathodic protection effect, which is also observed in Ref 12…”

State‐of‐the‐Knowledge on Coating Systems for Hot Stamped Parts

“…They explained this observation to the fact that a stable corrosion product consisting of the Fe–Si–Al compound filled the corrosion cavities, thereby, hindering the oxygen inward diffusion and the corrosion progress 28. Dosdat et al31 compared the corrosion resistance of aluminized, galvanized (GI), and galvannealed (GA) coatings after hot stamping. The coated panels were phosphated and painted.…”

“…The hot stamped GA coating had similar performance to the as produced GA specimen, but slightly inferior than the as produced GA coating due to its higher Fe content 50. Dosdat et al31 studied the corrosion resistance of aluminized coating, GI and GA coating after hot stamping. The coated panels were phosphated and painted.…”

Surface Oxide Formation during Rapid Heating of Zn-coated Press Hardening Steel

“…The coating does however not provide cathodic protection, and the corrosion of the underlying steel can occur in areas where the coating layer has been damaged during the diequenching. 15,16) Zn and Zn-alloy coatings have been developed to address this issue, as Zn and Zn-alloys have the advantage of providing cathodic protection to steel. The use of a Zn coating results in a mild form of liquid metal induced embrittlement (LMIE), characterized by microcrack formation and the presence of a thick ZnO layer at the surface after die-quenching.…”