Researchers from the Institute of Industrial Science at the University of Tokyo have devised a new method for bonding polymers to galvanized steel in a bid to manufacture lighter weight and more durable materials that can be produced at industrial scale.

Because traditional methods for bonding polymers to galvanized steel — which is steel coated with a layer of zinc — are typically unsuitable for mass production, oftentimes requiring harsh chemicals or specialized equipment, the team devised a better method.

Researchers at the University of Tokyo developed a method of bonding polymers with galvanized steel to create a lightweight and durable product. Source: Institute of Industrial Science, the University of Tokyo

To bind polymers to galvanized steel, which already demonstrates ideal mechanical properties and corrosion resistance for a host of applications including the automobile industry, the researchers pre-treated the steel with an acid wash and dipped it in hot water. While the acid wash reportedly stripped away the outer passive layer on the zinc coating of the steel, the hot water created nanoscale needle structures on the stripped surface of the galvanized steel.

When a polymer was then applied to the treated metal via injection-molded direct joining, the tiny gaps and ridges created by the hot water were subsequently filled, thereby creating extremely strong mechanical linkages.

"Our process can be adapted for a wide range of hybrid joining applications, in which metal and plastic parts need to be permanently bonded," explained the researchers. "Furthermore, our method does not use harsh chemicals or complicated procedures and thus is suited to the scale-up required for industrial application." This work could lead to optimization of polymer-metal joining which would be a significant asset to the manufacturing industry.

The process is detailed in the article, Effect of nanostructured zinc coating on high joining strength of polymer/galvanized high-strength steel composite via injection molding, which appears in the Journal of Manufacturing Processes.