Automotive corrosion protection - Interview with Aperam and Voestalpine

In the run-up to Automotive IQ's conference on Automotive Corrosion Protection, Aperam's Saghi Saedlou and Dr. Karl-Heinz Stellnberger from voestalpine gave us the opportunity to talk to them about the challenges of the topic and what they will be doing at the conference. Dr. Stellnberger, tell us a little bit about yourself. Where are you working at, what is your position, and what are you working on?

In short, I’m a corrosion expert for the automotive industry. I have been working for voestalpine, a steel producer in Austria, for the last 37 years. I am responsible for corrosion protection and thin film layers and head the R&D department in Linz, Upper Austria.

Could you give us a small glimpse of the presentation you will be giving at the conference?

The presentation concentrates on the most important and most dangerous corrosion problems to the car body and explains the corrosion process in a simple way.

It explains only the relevant corrosion damage which has ramifications to the end user of vehicles. The paint delamination due to mechanical damage, corrosion to flanged areas, damage during transport and corrosion accelerated by galvanic elements are covered in this presentation.

From this objective point of view, you can form your own subjective opinion and use the information in your specific situation with regards to protection against corrosion and the development of new products for the automotive industry. There is no reference to specific products or brands in the steel industry. The attendees are invited to use the information correctly, intelligently and eventually cost-effectively in the fight against corrosion.

With the integration of more and more diverse materials in the automobile, galvanic corrosion becomes more of a challenge. Are there solutions available?

Yes, but we can‘t prevent corrosion forever, we can use corrosion protection for the short life time of a vehicle. Isolation is the solution for this dangerous corrosion mechanism. Joints and sheet connections with different materials must be isolated electrochemically in the best way possible. You must prevent the anodic metal and follow the anodic/cathodic rule for corrosion protection.

Overall, corrosion protection on cars has improved very much over the years. Where do you think is still room for improvement? Why?

Not all automakers have improved their corrosion protection. Corrosion protection is a very expensive process. A paint shop in the automotive industry has a length of app. 3 to 5 km. It is the most expensive step in the production line.

When it comes to car bodies, where do you see the biggest challenges for corrosion protection? How will this change in the future? Why do you think so?

Weight reduction, new propulsion systems (electric/hydrogen), a wide variety of material usage, new coatings, generational transfer of know-how, simulation of corrosion processes etc. There are huge challenges for corrosion protection. We are in touch with the industry and these topics always come up.

Mrs. Saedlou, for starters, please introduce yourself. Where do you work, what is your position, and what are you working on?

I am located at the French Research Center of Aperam in the Stainless Steel Research Team. I am in charge of the Stainless Steel Solutions department which works on offering stainless steel solutions for the market. Our work consists of determining in use properties, limits of use of our stainless steel grades and coconception with customers to place the right grade to the right application.

When it comes to car parts, where do you see the biggest challenges for corrosion protection? How will this change in the future? Why do you think so?

I think that there are two big challenges concerning corrosion protection:

The first one is linked to safety issues. Car durability is still improved, and so any corrosion initiation is not admissible due to structural failure risk. With autonomous cars the crash parts will be reinforced and have to keep their integrity to insure their role. The second one is the cost of corrosion protection. With longer durability of the car, corrosion protection has to stay efficient during service life without costing more. A real challenge. New materials in the production process bring new challenges with them. How do you think will these be tackled? Are there already solutions available?

Our work is a good example on this point. It concerns stainless steel solutions through the hot stamping process. It was a double challenge to bring new material for structural parts AND a new process for this material. The change in surface made corrosion protection is a challenge and we found levers to offer a complete solution. Thus I think that this kind of issue can only be fixed when people consider the product as a solution and not only as raw material.

Overall, corrosion protection on cars has improved very much over the years. Where do you think is still room for improvement? Why?

Globally speaking improvement is always possible on lightweight and cost reduction, even concerning corrosion protection - even if today it is not the major point of interest to save cost through fuel consumption reduction.

For me the challenge today is in multi material. For mass production, the car of tomorrow will not be exclusively in aluminum or magnesium alloys, but will consist of a mixture of several materials. Then the durability of assembly (crevice corrosion and galvanic coupling) will be a topic of interest. In this context Ecoat treatment will probably have to be adapted to be compatible to all materials involved without price increase (or even with cost reduction if new materials allow it).

Could you give us a small glimpse of the presentation you will be giving at the conference?

Stainless steel application in the automotive industry is traditionally associated with the exhaust system. Sometimes we forget that, 30 years ago, the introduction of stainless steel for exhaust systems was a small revolution in car construction. Since then, several grades were developed to meet warranty requirements and to last in an ever more aggressive environment (temperature and media) and also due to more stringent emission regulations that introduced new sub-systems (DPF, EGR, DeNOx system…).

This experience led stainless steel companies to develop specific methodologies to characterize their grades while staying representative of in service conditions.

Recent innovations using hot stamping processes opened new possibilities concerning the material selection for automotive structures (Body-in-White and chassis). In this context, new martensitic stainless steel grades with high mechanical properties unlocked potential concerning lightweight and design. With these products presenting high mechanical characteristics, unexpected challenges emerged on the side of corrosion properties of stainless steel material.