Laser welding of polyamide-6.6 and titanium: a chemical bonding story

Hybrid materials are more and more common in biomedical applications, such as implants. However, assembling the materials is still challenging. Mechanical fastening solutions present durability problems, and adhesive solutions rarely combine strong mechanical properties and biocompatibility. To address these difficulties laser welding is a promising solution. It is a fast process with great design freedom that requires no additional material at the interface. Since the process is quite recent, the involved fundamental mechanism are not well understood. Hence this work aims at exploring the existence of a chemical bond between two materials: titanium and polyamide-6.6. Samples composed of a block of polyamide-6.6 welded to a titanium sheet were broken and analysed using XPS and ToF-SIMS. Results show more polymer in the weld and the chemical bond seems to be a complexation of titanium with the amide function

Laser welding of polyamide-6.6 and titanium:a chemical bonding story

Hybrid materials are more and more common in biomedical applications, such as implants. However, assembling the materials is still challenging. Mechanical fastening solutions present durability problems, and adhesive solutions rarely combine strong mechanical properties and biocompatibility. To address these difficulties laser welding is a promising solution. It is a fast process with great design freedom that requires no additional material at the interface. Since the process is quite recent, the involved fundamental mechanism are not well understood. Hence this work aims at exploring the existence of a chemical bond between two materials: titanium and polyamide-6.6. Samples composed of a block of polyamide-6.6 welded to a titanium sheet were broken and analysed using XPS and ToF-SIMS. Results show more polymer in the weld and the chemical bond seems to be a complexation of titanium with the amide function

Influence of Aluminum Laser Ablation on Interfacial Thermal Transfer and Joint Quality of Laser Welded Aluminum–Polyamide Assemblies

Laser assisted metal–polymer joining (LAMP) is a novel assembly process for the development of hybrid lightweight products with customized properties. It was already demonstrated that laser ablation of aluminum alloy Al1050 (Al) prior to joining with polyamide 6.6 (PA) has significant influence on the joint quality, manifested in the joint area. However, profound understanding of the factors affecting the joint quality was missing. This work investigates the effects of laser ablation on the surface properties of Al, discusses their corresponding impact on the interfacial thermal transfer between the joining partners, and evaluates their effects on the joint quality. Samples ablated with different parameters, resulting in a range from low- to high-quality joints, were selected, and their surface properties were analyzed by using 2D profilometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX). In order to analyze the effects of laser ablation parameters on the interfacial thermal transfer between metal and polymer, a model two-layered system was analyzed, using laser flash analysis (LFA), and the thermal contact resistance (TCR) was quantified. Results indicate a strong influence of laser-ablation parameters on the surface structural and morphological properties, influencing the thermal transfer during the laser welding process, thus affecting the joint quality and its resistance to shear load

Influence of laser ablation and plasma surface treatment on the joint strength of laser welded aluminum-polyamide assemblies

Laser assembly of a metal with a polymer is an innovative process for the development of hybrid lightweight structures. It was already demonstrated that surface treatment of aluminum prior to laser joining has a critical influence on joint strength of laser assembly with polyamide. In this work, further investigation of the influence of surface treatment prior to laser assembly is carried out. In particular, two kind of surface modification pretreatments of aluminum, laser ablation and plasma surface modification, in combination with plasma surface pretreatment of polyamide, were investigated. Surface properties of aluminum and polyamide after pretreatment are compared to their untreated state. More precisely, surface chemistry, surface energy and roughness characteristics are evaluated by X-ray photoelectron spectroscopy (XPS), sessile drop tests and 3D profilometry, respectively. Joint strength of laser assembly of treated aluminum and polyamide is reported. The more influential surface characteristics for the improvement of joint strength are determined, paving the way to significant advances in metal-polymer laser assembly technology

Chemical Bonds in Laser Welded Aluminum and Polyamide

Automotive industry is showing an increasing interest towards polymer/metal assemblies, essentially in order to increase fuel efficiency through the reduction of car body weight. In parallel, these assemblies are interesting for biomedical applications, because of the potential to obtain improved or new properties e.g. for implants. Laser welding is considered one of the most promising methods of joining dissimilar materials because of its unique advantages; the process is fast, can be adapted to complex geometries and is totally solvent free, which is a major asset for biomedical applications [1]. A strong adhesion between polyamide 6.6 (PA-6.6) and aluminum (Al) plates was obtained from laser welding in optimized conditions [2]. However, the root causes of this adhesion are not yet understood. Several effects may come into play, such as covalent binding, electrostatic binding, interdiffusion and mechanical interlocking. This is further complicated in “real life” samples by the high roughness of the metal sheet, the additives contained in the polymer, the Al and PA-6.6 surface composition and the difficulty to reach the metal-polymer interface. In order to gain information on the chemical binding between the oxydized Al surface and the PA-6.6, model samples were prepared by spin coating ultrathin PA-6.6 films on polished Al (99.999 % purity) plates (Fig. 1.). The two materials were subsequently welded by laser irradiation. FT-IR, XPS and ToF-SIMS have been used to carry out this study. The interface was reached by sputtering the polymer with low energy Cs+ ions in ToF-SIMS and Ar clusters GCIB in XPS. In this preliminary study, ions binding the Al with polymer were identified in both the positive (AlCH3O+, AlNH+, AlNH2 +, Al2NH+) AlCNO+, AlONH3 +) and negative polarities, (AlN-, AlNO-, AlCO-, AlCNO-). Depth profiles and images near the interface were obtained. Results obtained on our model samples will be compared with laser joints obtained on “real” samples. Ultimately, this work aims at providing guidelines for improving the mechanical resistance of the weld

Binding Mechanisms between Laser-Welded Polyamide-6.6 and Native Aluminum Oxide

[Image: see text] Nowadays, hybrid polymer/metal assemblies experience a growing demand in the industry, especially for transports and biomedical purposes. Those assemblies offer many advantages, such as lightweight structures and corrosion resistance. The main difficulty to assemble them remains. In this sense, laser welding is more than a promising technique because of its rapidity, the absence of intermediate materials, and its high design freedom. Unfortunately, several fundamental aspects are not well understood yet, as the chemical bonding at the interface. For this work, common materials are studied: polyamide-6.6 and aluminum. A previous published work strongly suggests the formation of a C–O–Al bond at the interface, but this information needs to be confirmed and the reaction mechanism is still uncertain. To achieve this goal, two different model samples were prepared. The first ones are spin-coated layers of polyamide-6.6 on mirror polished aluminum; the other samples are made of a layer of N-methylformamide mimicking the reactive part of the polymer, dip-coated on aluminum. Both sample types were analyzed with XPS and ToF-SIMS and display similar results: C–O–Al bond formation at the interface is confirmed and a reaction mechanism is proposed