Synchrotron characterization of alkaline cleaned ZM coated steel

Zinc coatings alloyed with aluminium and magnesium (ZM) have been of great interest in recent years for providing better corrosion performance than conventional hot dip galvanized steel (HDG) in the automotive industry. In addition, ZM has shown favorable stamping properties, higher production flow and less scrap from the stamping operation  providing a reduced coating thickness of 30% compared to HDG. These beneficial properties have been a main driver for many car manufacturers, to some extent replace HDG with ZM in exterior surfaces. However, the amount of alloying elements in the ZM coating effect the surface chemistry of the coating and results in a unique surface morphology with phases of different shape and composition. The microstructure strongly effects the formation of protective oxide layers and results in an inhomogeneous reactivity which can affect the effectiviness of the cleaning and pretreatment processes. 

The aim of this project is to investigate the surface chemistry of ZM coatings to understand composition on specific microscopic phases using a synchrotron-based surface analytical, X-ray photoemission electron microscopy (XPEEM) which has a high surface sensitivity and sub-micron spatial resolution. A detailed understanding of the surface chemistry is necessary to solve  issues in the washing process and ensure proper pretreatment formation on the surfaces prior to painting.

The project is coordinated by RISE and performed in collaboration with Volvo Cars.