Diffusion at the interface of laser welded polyamide-6.6 and aluminum assemblies

Polymer/metal assemblies are widely used in industry, especially the automotive industry, to get more cost efficient and light weight structures. Although they present many advantages, their assembly remains challenging. Laser welding is an effective solution. Indeed, it is fast, presents high design freedom, and does not require any interstitial material. Furthermore, surface pretreatment can tune mechanical resistance. However, the root causes of adhesion remain partly unknown. The existence of chemical bonding at the interface has already been established, but other adhesion phenomena, such as diffusion, remain to be investigated. The aim of this study is to investigate the existence of diffusion at the interface between the polymer and the metal after laser welding. Therefore, a common material combination was used: polyamide-6.6 and aluminum. A thin film of polyamide-6.6 was deposited on mirror-polished aluminum, and two depth profiles out and in the weld were acquired by ToF-SIMS and compared. The results show that the diffusion of aluminum occurs at the interface of polyamide-6.6, with a diffusion length of approximately 22 nm.