Surface Control of High Strength Steel for Galvanization

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To be able to develop and produce smarter materials in an environmental and economical way, more flexible technologies are required. One such a potential breakthrough technology is flexible high-speed Physical Vapour Deposition (PVD). In this process, a vapour is generated in a vacuum and then sprayed onto a strip, thus forming a thin solid film. This technology allows the deposition of a unique selection of coatings onto high quality strip products enabling the optimization of both the substrate and the coating. Motivation to pursue PVD technology not only lies in its future applications, but also in current issues. The automotive industry is pushed to reduce CO2 emissions and improve fuel economy, and one route to achieve this is reducing vehicle weight. Cars can be made lighter by using coated novel Advanced High Strength and Ultra High Strength (UHSS) Steel grades as they deliver the same strength in thinner sections. These steel grades are produced with relatively high alloy levels of Mn, Si and Al. However, such alloying additions influence the coatability for corrosion (typically Zn galvanising), which results in different coating recipes for each steel grade. Some grades are impossible to coat with Hot Dip Galvanizing. Hence, to be able to assist the automotive industry in achieving the future weight saving both steel grade and coating development are essential. The flexible PVD technology will make it possible to coat this range of UHSS and will enable the manufacturing of future substrate/coating systems with an enhanced performance that can presently not be produced. This PhD project in collaboration with Tata Steel Europe will address the following research questions: How can the oxide formation and type be controlled during the strip production?How do different oxides affect the coating performance - adhesion, surface appearance, corrosion? How can the oxides be removed from the strip before coating - e.g, plasma cleaning?How does the thickness/stress in the Zn/ZnMg coating layer on top of the substrate influence the overall performance?