The Influence of PSA Pre-Anodization of AA2024 on PEO Coating Formation: Composition, Microstructure, Corrosion, and Wear Behaviors

In the frame of the current work, it was shown that plasma electrolytic oxidation (PEO) treatment can be applied on top of phosphoric sulfuric acid (PSA) anodized aluminum alloy AA2024. Being hard and well-adherent to the substrate, PEO layers improve both corrosion and wear resistance of the material. To facilitate PEO formation and achieve a dense layer, the systematic analysis of PEO layer formation on the preliminary PSA anodized layer was performed in this work. The microstructure, morphology, and composition of formed PEO coatings were investigated using scanning electron microscopy (SEM), x-ray diffraction (XRD), and glow-discharge optical emission spectroscopy (GDOES). It was shown that under constant current treatment conditions, the PSA layer survived under the applied voltage of 350 V, whilst 400 V was an intermediate stage; and under 450 V, the PSA layer was fully converted after 5 min of the treatment. The comparison test with PEO formation on the bare material was performed. It was confirmed that during the "sparking" mode (400 V) of PEO formation, the PEO coatings, formed on PSA treated AA2024, were more wear resistant than the same PEO coatings on bare AA2024

Mistet på sjøen? En nyoppdaget fiskekrok fra steinalderen i Søgne, Vest-Agder.

The starting point for the present paper is a recent discovery of a well-preserved bone or antler fishhook, which turned up in a test pit during an underwater survey outside Tømmervigodden in Søgne, southernmost Norway. The hook is the third archaeological bone find from submarine context in Søgne. Tømmervigodden is located two kilometers away from Hummervikholmen, a submarine site known for revealing the oldest human remains from Norway, dated to the Middle Mesolithic (c. 8300-6300 cal. BC). Furthermore, a harpoon has been found in Lundeelva, approx. eight kilometers inland to the northeast. These finds demonstrate the extraordinary conditions for preservation of organic remains in the area. This article present the artefact and we discuss the issue of dating and deposition based on typology, context, and shoreline displacement curves. How old is the fishhook? How did it end up in the sea, and why is it so well preserved? The site is located in one of three areas along the Norwegian coast with potential for transgressed Mesolithic sites. The sea levels has fluctuated in Vest-Agder since the end of the Ice Age, and the sea has periodically been both higher and lower than today.The location close to Hummervikholmen and another Mesolithic site located on dry land at Tømmervigodden, initially suggested a Mesolithic date. However, the form of the fishhook, with a barb and elongated knob for attachment of the line, differs considerably from well-dated Mesolithic fishhooks in the region. The newly discovered fishhook has a distinct barb, an attribute previously considered a Neolithic trait. A precise dating would be crucial, but the closest typological parallels are undated stray-finds and C14-analysis would have destroyed the small object. Hence, dating of the hook requires a new assessment of the typology and chronology of the Stone Age fishhooks. Based on chronological and regional comparisons, we argue for a Middle Neolithic date of the fishhook from Søgne. Based on current knowledge of the local shoreline displacement curve and the formation processes influencing the seabed, we further suggest that the fishhook was lost at sea during fishing, when the sea level was at least five meters above present

Zn-Al LDH growth on AA2024 and zinc and their intercalation with chloride: Comparison of crystal structure and kinetics

The dissimilarities and features of the crystal structure of ZnAl LDH-NO3 conversion layers grown directly on pure zinc and aluminum alloy 2024 were investigated in the present paper. Although the nature of the cations in the double hydroxides are the same in both cases (Al3+ and Zn2+), their sources differ according to the substrate. This leads to a difference in the cationic layers and interlayer structure, which consequently influences the anionic exchange reaction. In the frame of this work, the kinetics of the anion-exchange of nitrate by chloride was investigated as well as the crystal structure of the resulting ZnAl LDH-Cl on both substrates. Synchrotron high-resolution X-ray diffraction was the main method to obtain structural information and was supported by additional calculations and scanning electron microscopy.The current study revealed noticeable changes on the positioning of the interlayer atoms for the ZnAl-LDH-Cl on zinc in comparison with the ones on AA2024 substrate