Atmospheric corrosion and impact toughness of steels: Case study in steels with and without galvanizing, exposed for 3 years in Rapa Nui Island

Contributions to a More Realistic Characterization of Corrosion Processes on Cut Edges of Coated Metals Using Scanning Microelectrochemical Techniques, Illustrated by the Case of ZnAlMg-Galvanized Steel with Different Coating Densities

Corrosion processes at cut edges of galvanized steels proceed as highly localized electrochemical reactions between the exposed bulk steel matrix and the protective thin metallic coating of a more electrochemically active material. Scanning microelectrochemical techniques can thus provide the spatially resolved information needed to assess the corrosion initiation and propagation phenomena, yet most methods scan cut edge sections as embedded in insulating resin to achieve a flat surface for scanning purposes. In this work, the galvanized coatings on both sides of the material were concomitantly exposed to simulated acid rain while characterizing the cut edge response using SECM and SVET techniques, thereby maintaining the coupled effects through the exposure of the whole system as rather realistic operation conditions. The cut edges were shown to strongly promote oxygen consumption and subsequent alkalization to pH 10-11 over the iron, while diffusion phenomena eventually yielded the complete depletion of oxygen and pH neutralization of the nearby electrolyte. In addition, the cathodic activation of the exposed iron was intensified with a thinner coating despite the lower presence of sacrificial anode, and preferential sites of the attack in the corners revealed highly localized acidification below pH 4, which sustained hydrogen evolution at spots of the steel-coating interface.

Accelerating stabilization of weathering steel through rust modification pre-corrosion treatment

To accelerate the formation of the protective rust layer on weathering steel, a new pre-corrosion method containing a replacement reaction was explored. This process was mixed with Cu in the pre-corrosion rust layer to imitate the enrichment of alloying elements through long-term corrosion. By using various analysis methods, the initial corrosion behavior of weathering steel and carbon steel with/without pre-corrosion treatment was studied under indoor wet-dry cycle conditions. The results showed that the pre-corrosion treatment covers the steel surface with a rust layer containing high-concentration Cu. Subsequently, the corrosion uniformity of the weathering steel was significantly improved, and the protective performance of corrosion products was enhanced due to the high concentration of Cu enrichment. This technology is expected to provide a new way to perfect the service performance of weathering steel at the initial stage of application.