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ABSTRACT: Conditions for forming zinc phosphate conversion coatings on AA6061 aluminum alloy have been investigated by characterizing coatings formed for different parameters of the coating bath. Morphological and compositional information on the coatings was assessed by SEM, EDX and XPS, and simple adhesion tests were undertaken to indicate the strengths of coating attachment. The emphasis was to identify conditions that give high coverage, uniform coatings of small, strongly adhered, zinc phosphate crystals. The use of low-zinc solutions (e.g. an atomic Zn/P ratio of 0.07) and normal-zinc solutions (Zn/P ratio 0.25) were compared; coatings formed by the two solution types appear comparable at pH 2, although at pH 4 the low-zinc solution is more effective. Fluoride in the concentration range 200–400 ppm is indicated to be a useful additive for the normal-zinc coating bath and in the 600–1000 ppm range for the low-zinc process. The use of acid etching in the pre-treatment appears to yield better coatings than when mechanical polishing alone is used.
Journal of Materials Science 07/2001; 36(16):3941-3946. · 2.02 Impact Factor
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ABSTRACT: Chromate conversion coatings formed on samples of 2024-T3 aluminum alloy, which had been given different pre-treatments, were examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and corrosion tests. Two pre-treatments were considered, namely a simple mechanical polish, and polishing followed by an etch in a HF-H2SO4 solution. The latter treatment leads to significant Cu enrichment at the oxide-alloy interface, and this in turn can lead to a deleterious effect on the corrosion protection afforded by a subsequently applied chromate coating. Discussions are given of the behaviour of Cu in the coating formed on the sample that received an acid etch in the pre-treatment. This involves both migration through the coating and a non-uniform redeposition of Cu on to the coating surface. By contrast, the sample that initially was given just the mechanical polish in the pre-treatment does not show a Cu enrichment in the surface region, and the subsequently applied coating appeared stable after a 24 h immersion in a NaCl test solution.
Journal of Materials Science 01/2001; 36(13):3215-3220. · 2.02 Impact Factor
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ABSTRACT: 7075-T6 aluminium alloys panels were surface conditioned in a titanium colloid suspension, under a variety of different conditions, and subsequently these samples were immersed in a ZnO + H3PO4 coating mixture, and the phosphate coating layers characterized. Morphologies observed by scanning electron microscopy (SEM) reveal that the coating layer consists of two phases, namely an amorphous phase, which is directly bonded to the substrate, and a crystalline phase, in which larger crystal grains grow on top of the amorphous base. Chemical compositions of the coating layers were analysed by X-ray photoelectron spectroscopy (XPS) and by static and imaging secondary ion mass spectroscopy (SIMS). It is found that the details of the surface conditioning affect the final coating, both in terms of morphology and chemical composition. For example, larger amounts of Zn and P are detected in coatings for which the initial conditioning is done at 40C, compared with room temperature; a similar statement can be made for surfaces which are water rinsed after the Ti pretreatment, compared with those which are not water rinsed prior to the coating treatment.
Journal of Materials Science 12/1995; 31(3):565-571. · 2.02 Impact Factor
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Journal of Materials Science Letters 12/1994; 14(20):1461-1463.
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ABSTRACT: X-ray photoelectron spectroscopy (XPS), combined with scanning electron microscopy (SEM), weight loss tests and atomic absorption spectroscopy (AAS), has been applied to investigate the corrosion protection properties of zinc phosphate when coated on 7075-T6 aluminium alloy. XPS is consistent with the coating process leading to both physically adsorbed and chemically absorbed zinc. The former is washed away by ultrasonic washing, but the chemically absorbed component, identified as ZnO
x
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Journal of Materials Science 02/1994; 29(5):1368-1373. · 2.02 Impact Factor
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Journal of Materials Science Letters 12/1992; 12(11):844-846.
