The nanoscale needle structures that form on the surface of treated galvanized steel. Image: Institute of Industrial Science, The University of Tokyo.
The nanoscale needle structures that form on the surface of treated galvanized steel. Image: Institute of Industrial Science, The University of Tokyo.

The manufacturing industry is constantly on the lookout for more efficient manufacturing materials, but most new methods for developing such materials in the lab are not suited for industrial-scale use. Now, investigators from the Institute of Industrial Science at the University of Tokyo in Japan have developed a cheap and simple method for bonding polymers to galvanized steel – steel with a coating of zinc over its surface – to create a lightweight and durable material that can feasibly be produced on an industrial scale.

As the manufacturing sector becomes increasingly aware of the environmental impact of its processes, new techniques are needed to ensure that parts can be made both sustainably (with a minimum of harsh chemicals and waste) and with a long lifetime before needing to be replaced. Galvanized steel is widely used in the automobile industry owing to its excellent mechanical properties and corrosion resistance.

However, because of the weight of galvanized steel, polymer-metal composites are increasingly being applied as alternative lightweight materials with high durability. Unfortunately, traditional techniques for bonding polymers to galvanized steel are unsuited for mass production as they often require harsh chemicals or specialized equipment.

In a paper in the Journal of Manufacturing Processes, researchers from the University of Tokyo report a new method for bonding a polymer to galvanized steel by simply pre-treating the steel with an acid wash and dipping it in hot water. The acid wash strips the outer ‘passive layer’ from the zinc coating, allowing the hot water to form rough nanoscale needle structures on the surface.

The researchers discovered that when they applied a polymer to the treated metal (in a process called injection-molded direct joining), it filled the tiny gaps and ridges between and within the needle structures, creating very strong mechanical linkages. “We found that immersion in hot water was a simple and effective method for producing nanoscale structures on the zinc coating for the polymer to adhere to, but that prior acid-washing to remove the passive layer was a necessary step for this to occur,” explains lead author Weiyan Chen.

The group also showed that the force the polymer could withstand before being torn off the metal, known as the tensile-shear strength, increased with the complexity of the nanoscale structures on the galvanized steel surface. By optimizing the hot water temperature and treatment time to achieve peak complexity in the nanoscale structuring, the team was able to significantly increase the tensile-shear strength compared with untreated metal.

“Our process can be adapted for a wide range of hybrid joining applications, in which metal and plastic parts need to be permanently bonded,” says senior author Yusuke Kajihara. “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 the optimization of polymer-metal joining, which would be a significant asset to the manufacturing industry.

This story is adapted from material from the University of Tokyo, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.