Microstructural effect on the wear behaviour of the hard-anodised aluminium alloys EN AW-6082 and EN AW-7075

The suitability of hard-anodising of high-strength Al alloys (EN AW-7075-T651) for the fabrication of protective coatings which are also applicable on screws was investigated. A medium-strength AlSilMgMn alloy (AA60682-T6), generally rated as applicable for anodising, was used as reference material. After possible setting phenomena of a screw joint, the load-bearing surface of the screw can be subjected to an oscillating relative movement. The damaging tribological load was simulated in an oscillation wear test. The resulting wear appearances have revealed that the untreated oxide coatings on the EN AW-6082 substrate are not capable of providing protection against tribological load. Since hot-water sealing increases the hardness of the coating but also contains the technology-induced risk of softening the substrate material, other tribological protection methods have been looked for. The analysis of the tribological tests (characterisation of the structure and the resulting properties of the material, measurement of the wear amount and analysis of the wear appearance) have shown that the films sealed with wax emulsion on both substrate materials are the most promising candidates for the application of devices under oscillation wear. The obtained roughness, friction coefficients and hardness values confirm the positive behaviour of the anodically oxidised EN AW-7075-T651 alloy under the chosen tribological load.