Metallization of a polymer using cold spray: Application to aluminum coating of Polyamide 66

Numerous automotive and aircraft/aerospace applications involve metallic coating of organic matrix composite materials, e.g. for aesthetic, electric, or engineering functions. In the thermal spray process family, cold spray is very attractive for the achievement of metallization of low-temperature resistant materials such as organic composites, due to its “cold” characteristic. However, despite the current (and justified) craze for cold spray, little is still known about the potential of this process for this type of application.

      The present work investigated into cold spray of aluminium onto PA66 (polyamide-Nylon 66) and 30% glass fiber-reinforced PA66. The study showed that the key point for the success of the metallization was the creation and control of a so-called “intermediate layer” between the coating itself and the substrate. This intermediate layer was made of Al mixed with PA66 (and fibers), which resulted in a transition from the substrate to the coating. All the major features, e.g. thickness, Al content and distribution, in-depth gradient, relevant to the intermediate layer were determined as a function of processing conditions, i.e. spray parameters and particle size. This involved both 2-dimensional (2D) and 3-dimensional (3D) observation and analyses using scanning electron microscopy (SEM), X-ray MicroTomography (XMT), White light profilometry, and quantitative image analysis. Basic mechanisms which govern the formation of the intermediate layer are discussed in the light of the viscoelastic behavior of PA66 in dynamic conditions and of the Al particle size and morphology. The influence of intermediate layer characteristics on the coating-substrate bond strength was studied using innovative LAser Shock Adhesion Testing (LASAT^®).

      The work demonstrated the feasibility of cold spray for satisfactory metallization of PA66-matrix composites with Al. This paves the way for using cold spray as an advantageous substitute process for the industrial protection of polymer-based composites.