By Josh Perry, Editor
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German researchers have developed new continuous infrared laser technique for pretreating aluminum sheets to better adhere with thermoplastic polyamides in injection molding applications to create stronger lightweight materials, according to a report from the American Institute of Physics.

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. (Matthieu Fischer)

The researchers found that by roughening the surface of the aluminum sheets with laser beams to create adhesive for a polyamide layer to molded over. The sheets were put into and injection mold and overmolded with thermoplastic polyamide.

“Tests using optical 3-D confocal microscopy and scanning electron microscopy revealed that the aluminum sheets treated with pulsed lasers enjoyed much smoother line patterns in the trenches on their surfaces than those pretreated with continuous laser radiation,” the report explained. “Aluminum sheets treated with infrared lasers also exhibited stronger bonding, but these properties diminished in tests with increasing levels of moisture.”

Researchers are continuing to study the process and the materials to optimize the process and make it more viable for manufacturers. One issue that remains is thermal contraction of the thermoplastics when cooled and the mechanical stresses that result.

The research was recently published in the Journal of Laser Applications. The abstract read:

“The aim of this work is to investigate the influence of surface structures on the adhesion strength of metal-plastic hybrids. Aluminum substrates were structured with continuous wave and picosecond pulsed laser systems and overmolded with a thermoplastic polyamide material.

“The materials were examined in terms of structure topography, molding accuracy, and a tensile shear test. It was found that the surface pretreatment by laser structuring with continuous wave laser enhances the effective joining surface, creates a mechanical interlocking, and increases the adhesion strength of the hybrid compared to the untreated condition significantly.

“A shear strength of 11.9 MPa was achieved, which exploits 90% of the pure polyamide properties.”