Failure mechanism analysis based on laser-based surface treatments for aluminum-polyamide laser joining

The development of strong metal to polymer assemblies is currently an important research subject thanks to its
prominence to develop lightweight structures. Furthermore, laser welding is known to be a fast, reliable, and
versatile joining process, and it was demonstrated recently that it can be applied to such metal to polymer
systems. To enhance the mechanical properties of the laser-joined aluminum-polyamide (Al-PA) specimens, laser
polishing and laser ablation processes have been implemented on the aluminum surface before joining. The
polyamide surface was also treated with the laser beam, separately. The surfaces were tested by several characterization
techniques before and after each surface treatment. Then aluminum and polyamide samples with
different surface treatments have been joined with an identical laser joining process. The mechanical properties
of the joints in single lap shear configuration are reported and the failure mechanisms are discussed based on
micro-computed x-ray tomography imaging of joined specimens and microscopic analysis before failure. Results
show that both surface treatments of aluminum significantly improve the shear load of the joint; however, with
different failure mechanisms. Polyamide surface treatment and increasing degree of crystallinity are effective
when combined with the laser polishing of the Al surface. This combination is responsible for further
enhancement of the shear load of the joint to the limit of base metal strength which is approximately 60 %
improvement compared to the untreated samples. Finally, energy dispersive X-ray mapping shows the physicochemical
bonding between aluminum oxide and polyamide at the interface.