Metal-Plastic Bonding Gets Stronger Through Laser Treatment

Designing lightweight materials -- a goal in the automotive and airline industries -- requires carefully joining together different types of materials like metals and polymers, and these additional steps drive up manufacturing costs. New work in laser technology recently increased the adhesion strength of metal-plastic hybrid materials; engineers demonstrated a technique for binding plastic to aluminum by pretreating sheets of aluminum with infrared lasers. They discuss their work in the Journal of Laser Applications. This image shows SEM images of (a) aluminum swarfes at the edges of the continuous wave laser structure and (b) remaining aluminum in the trenches of the molded polymer surface after tensile shear test. (Image courtesy of Matthieu Fischer.)

The design of efficient and durable vehicles from sturdy, light-weight materials is still an important objective in the airline and automotive industries. However, the process of creating light-weight materials usually requires a careful joining together of different kinds of materials—such as polymers and metals—through specialized processes.

One such process is injection molding, which involves generating and “molding” the plastic component over the metal component within the machine’s cavity. As expected, this process tends to be more difficult when compared to other joining technologies (such as thermal pressing), mainly because of the high level of thermal specificity required.

In order to tackle this problem and also create a stronger metal-plastic bond, a new technique involving the roughening of the metal surface with laser beams before over-molding with plastic, was developed. Two approaches were employed in this technique: one was to pretreat the aluminum surface with continuous laser beams and the other involved using a laser beam pulsed for 20 picoseconds at a time.

The pretreated sheets were then placed in an injection mold and over-molded with a layer of thermoplastic polyamide. Upon completion, the surface topography of the hybrid material was examined and a series of mechanical tests were conducted to understand the bonding behavior of the materials and which conditions produced the greatest bonding strength.

With the aid of electron microscopy and 3D confocal microscopy, it was observed that the aluminum sheets pretreated with pulsed lasers had trenches with smoother line patterns when compared to those treated with continuous lasers. In the end, the results revealed that the aluminum sheets pretreated with infrared lasers exhibited a stronger bonding than that of the untreated sheets.

And although more research is still required on this subject, to understand issues like how the bonding behaves under increasing moisture levels, the initial results are certainly promising and may very well ease up the metal-plastic hybridization process in the near future.

This study was conducted by a group of German scientists from Technical University Dresden, Leibnitz Institute for Polymer Research and The Fraunhofer Institute for Material and Beam Technology. The full details of their findings are published in the Journal of Laser Applications.

For more interesting laser research, check out Raytheon Test Fires a Laser Weapon From a Chopper.