The galvanisation process has been in use in the automotive industry, specifically in advanced markets, since the 1980s. The North American market completely shifted from painted cold rolled sheet steel to painted galvanised sheet steel body panels in the 80s and 90s in a bid to reduce the amount of rusting that happens on the vehicles’ body, thereby reducing safety issues arising out of weak body panels.
The Indian Institute of Technology, Bombay (IIT Bombay), with the support of the International Zinc Association conducted a study on the amount of rust that car bodies – using cold rolled sheet steel instead of galvanised steel – face in the coastal areas of Chennai. Auto Tech Review caught up with Dr Dough Rourke, Consultant – International Zinc Association (IZA), Canada, (Above) and Prof Anand Khanna, Former Professor, Department of Metallurgy Engineering, IIT, Bombay (Below) to get their perspectives on the use of galvanised steel in car manufacturing among others.
GALVANISATION & ITS BENEFITS
The key areas of a car that leverages galvanised steel sheets include the Body-in-White (BIW) and closure panels, in order to provide corrosion-free vehicles, said Dr Rourke. The use of this processed steel is becoming a standard in markets across the world, save for India, which given its large passenger vehicle sales should mandate a certain amount of galvanised steel during production, in order to make vehicles safer, he noted.
The galvanisation process applies a layer of zinc, which keeps moisture, salt, and corrosive atmospheres away from the steel. Zinc is electro-chemically more active than steel, which acts as a deterrent to the possibility of rusting. Zinc offers cathodic protection, and sacrifices itself during small damages, thereby preventing the steel beneath it from corroding.
Galvanised steel sheets are used for body panels, which is then coated with the top layer of paint, so as to offer two layers of protection before any damage can reach the vehicle body. While the paint provides barrier protection over thin zinc coating, the underlying zinc coating greatly extends paint life by preventing steel corrosion and undercutting the paint film. This ‘duplex’ system lasts a number of times longer than a single coating on its own, thereby providing a synergetic solution, explained Dr Rourke. The main result of switching to galvanised steel sheets is that corrosion warranties can be applied on all vehicles, since the cosmetic and perforation effects are taken care of.
PROJECT ON RUSTING
The IIT Bombay study showcased the extent of corrosion taking place on different car body parts for various brands in the coastal region of Chennai. It included a survey of about 500 cars aged 1-16 years, across locations such as parking lots, open and sheltered areas, as well as on the beach front. These included cars from a variety of brands costing less than ` 10 lakh. The study used the methodology to check for visible perforations, paint blisters, and surface red rust.
The IIT report based on the survey showed that there is a corrosion problem affecting the durability and the eventual safety of cars in India. The study was then repeated selecting only Indian made cars using galvanised steel. This report revealed that the percentage of cars in the similar age group showing corrosion defects was observed to be drastically lower.
On an average, Indian car manufacturers use about 20-25 % galvanised steel for models manufactured and sold in the domestic market. However, these same manufacturers use over 70 % galvanised steel for the same models they export to markets in Europe, Asia and Africa. In addition, it is important to note that the vehicles for domestic sales, as well as export markets are produced from the same stamping and assembly facilities.
Car companies are not presently using galvanised steel for the domestic market because Indian consumers are not demanding it, and it is not mandated by law, the report said. The lack of legal requirements in India for the amount of galvanised steel to be used leads manufacturers to offer the same models for domestic sales with a far lower percentage of this processed steel, noted Dr Rourke.
On repair of such galvanised steel in contrast to regular cold rolled sheet steel, Prof Khanna said it is almost identical in nature. While damage may chip the top layer of paint alone, or extend into the layer of zinc, the repair work of denting and repainting remains unchanged for either type of steel used. Since a higher percentage of galvanised steel is used in the BIW, rather than the outer shell, it is seldom that repairs are needed in those parts of the vehicle.
There is an obvious advantage in covering a higher percentage of BIW and vehicle closure panels with galvanised steel, as opposed to cold rolled sheet steel. The main factor of additional cost is also something that is already covered, since almost all manufacturing facilities of OEMs already have the infrastructure to create galvanised steel. It is as simple as increasing the quantity of steel required for the body and outer shell to be put through the galvanising process before being assembled onto the vehicle.
IZA is in talks with OEMs on the advantages associated with galvanisation, for which it is receiving encouraging feedback. It is also working with steel companies to make products that add to the strength and can bring out the galvanisation benefits better.
TEXT: Naveen Arul