For aluminum alloys, anodizing is a common electrochemical surface treatment to allow for protection against corrosion and wear. The produced conversion layers are first sealed in industrial processes to further enhance the corrosion protection by closing the coating surface pores. In their lifetime, anodized components often undergo cyclic loadings. However, despite the relevance of a sealing treatment, there is a lack of systematic studies regarding its influence on the fatigue behavior of anodized aluminum components. In this work, a 6082-aluminum alloy was anodized in sulphuric acid and the effect of the anodizing treatment with and without further hydrothermal sealing on the fatigue strength was investigated. The thickness and Martens hardness of the coatings were determined and the coating appearance in non-sealed and sealed conditions was analyzed by scanning electron microscopy prior to and after cyclically loading at R = −1. The fatigue strength was significantly decreased by the anodizing treatment, when compared to the bare substrate. However, hydrothermal sealing had a positive influence as the anodized and sealed condition attained a fatigue strength in the range of the bare aluminum. Distinct differences regarding the coating appearances, thickness, and hardness were not observed when comparing the non-sealed and the sealed conditions. After fatigue loading, numerous pronounced radial cracks were present in the anodic coating, but the number of cracks were significantly lower for the hydrothermally sealed coating. Fatigue failure occurred due to propagation of one crack from the coating towards the substrate, resulting in single-point crack initiation, which was similar to the fatigue fracture behavior of the bare aluminum substrate.

In this work the high cycle fatigue behavior of a particulate reinforced 2124 aluminum alloy, manufactured by powder metallurgy, is investigated. SiC particles with a size of 3 μm and 300 nm and a volume fraction of 5 and 25 vol %, respectively, were used as reinforcement component. The present study is focused on the fatigue strength and the influence of particle size and temperature. Systematic work is done by comparing the unreinforced alloy and the reinforced conditions. All of the material conditions are characterized by electron microscopy and tensile and fatigue testing at room temperature and at 180 °C. With an increase in temperature the tensile and the fatigue strength decrease, regardless of particle size and volume fraction due to the lower matrix strength. The combination of 25 vol % SiC particle fraction with 3 μm size proved to be most suitable to achieve a major fatigue performance at room temperature and at 180 °C. The fatigue strength is increased by 40% when compared to the unreinforced alloy, as it is assumed the interparticle spacing for this condition reaches a critical value then.

In this study, an attempt was made to improve the mechanical properties and in particular the strength of a precipitation-hardenable aluminum alloy while still maintaining high ductility. For this purpose, AlSi7Mg0.6 (A357) powder with an average particle diameter of d₅₀ = 40 µm was consolidated using field assisted sintering technique (FAST), and two material conditions were compared: an as-sintered and an underaging heat treated condition (T61). Mechanical properties were determined using tensile tests and hardness measurements. In addition, the microstructure was investigated by optical microscopy. Further, porosity and density were analyzed after the different heat treatments. By the underaging heat treatment, the surface hardness was increased by 100% and the yield strength was increased by 80% compared to the as-sintered material. However, the elongation to failure dropped to one third of that of the as-sintered material. Presumably, this effect was a result of an increased porosity due to the heat treatment. It is assumed that the observed pores were generated by artefacts from the FAST process used to manufacture the samples. The internal gas pressure and equilibrium diffusion supported by heat treatment temperature, and the reduction in surface energy caused by coalescent micropores, led to the enlargement of previously undetectable inhomogeneities in the as-sintered material that resulted in pores in the heat-treated sintered alloy.