Mechanical interlocking has been proven to be an effective bonding mechanism for dissimilar material groups like polymers and metals. Therefore, this contribution assesses several surface pretreatments for the metallic adherent. Blasting, etching, combined blasting and etching, thermal spraying, and laser structuring processes are investigated with regard to the achievable interlaminar strength and the corresponding surface roughness parameters. The experiments are carried out on EN AW-6082/polyamide 6 polymer-metal-hybrids, utilizing a novel butt-bonded hollow cylinder specimen geometry for determining the shear and tensile strength. The experimental results indicate that the surface roughness slope has a major impact on the interlaminar strength. A laser-generated pin structure is found to provide the best mechanical performance as well as the highest surface slope of all investigated structuring methods.

The surface hardening of single-face-centred cubic (fcc)-phase CrMnFeCoNi and the manganese-free CrFeCoNi alloy was conducted using low-temperature nitrocarburisation. The microstructural investigations reveal the successful formation of a homogeneous diffusion layer with a thickness of approximately 16 µm. The interstitial solution of carbon and nitrogen causes an anisotropic lattice expansion. The increase in microhardness is in accordance to the graded concentration profile of the interstitial elements. Wear tests show a significantly enhanced resistance at different loads. The electrochemical tests reveal no deterioration in the corrosion resistance. The absence of precipitates is proven by microstructural investigations. The results prove the applicability of the concept of solution hardening by the formation of supersaturated solutions for the material group of high-entropy alloys. Hence, an increase of entropy with the consideration of lattice interstices provides new development approaches.

The interlaminar strength of mechanically interlocked polymer–metal interfaces is strongly dependent on the surface structure of the metal component. Therefore, this contribution assesses the suitability of the fractal dimension for quantification of the surface structure, as well as interlaminar strength prediction of aluminum/polyamide 6 polymer–metal hybrids. Seven different surface structures, manufactured by mechanical blasting, combined mechanical blasting and etching, thermal spraying, and laser ablation, are investigated. The experiments are carried out on a butt-bonded hollow cylinder testing method that allows shear and tensile strength determination with one specific specimen geometry. The fractal dimension of the metal surfaces is derived from cross-sectional images. For comparison, the surface roughness slope is determined and related to the interlaminar strength. Finally, a fracture analysis is conducted. For the investigated material combination, the experimental results indicate that the fractal dimension is an appropriate measure for predicting the interlaminar strength.

In this study, various structuring methods for creating adhesion by mechanical interlocking in the interface of metal/FRP (fiber-reinforced polymer) joints are investigated. A novel processing route using thermal spray coatings as additive structure is presented. Different coating systems are first assessed by axial loading tests with spray-coated plungers for the evaluation of the additive layer adhesion on the metallic base material. Additional microstructures, produced by different abrasive processes (corundum blasting, laser structuring, and fine milling) are compared with the additive structures. All surface structures are characterized by electron microscopy for two sheet materials: DC06 and AA6016-T4. The abrasive structures show a significant material dependence, while the selected coating system offers the adjustment to different base materials by an independent surface layer. The structured metal sheets were further joined to glass-fiber-reinforced polyamide 6 (PA6) by hot pressing to evaluate the interface properties in tensile shear tests. The results confirm a suitability of thermal spray coatings for providing a high bonding strength in metal/FRP joints for both investigated metallic substrate materials.

The lap shear test is a common method for determining the interlaminar shear strength of material compounds due to its simplicity with regard to specimen production and experimental realization. However, the obtained results strongly depend on the material pairing and the specimen geometry, which have a significant influence to the stress state within the interface during the experiment. A torsion test method using butt-bonded hollow cylinders seems more appropriate due to the expected more homogeneous shear stress distribution. The aim of this work is to compare both testing methods by experimental and numerical investigations. A comparative study with thermally joined aluminum-polyamide hybrid compounds was performed. The corresponding simulations were carried out with the commercial FE-software Abaqus™, using a user defined material model for the thermoplastic joining partner and the built-in cohesive behavior contact property for modelling interfacial damage.

Laser structuring is by far the most investigated metal surface-pretreatment method for creating adhesion in polymer–metal hybrids. Especially, cone-like protrusions show excellent wetting behaviour as well as high compound strength. However, the processing time is extremely high. Therefore, this paper assesses a process strategy for creating pin structures with scalable height by single pulse drilling with an Nd/YVO₄ nanosecond laser system on EN AW-6082 aluminium alloy. The strength testing is carried out by butt-bonded hollow cylinder torsion. The samples are manufactured by heat-conduction thermal joining with polyamide 6. Ten different surface structures with two different ablation diameters are investigated and compared to cone-like protrusions in terms of processing time, wetting behaviour, shear strength and fracture behaviour. The experimental results show that pulse drilling pins structures with high aspect ratio reach-strength values close to cone-like protrusions but with 31 times higher processing rate.