“…3 c and d). A similar effect is known for PEO of Al–Si alloys as the inheritance of chemical inhomogeneity in the oxide layer from Si-particles of silumin [ 50 ]. Fig.…”
“…3 c and d). A similar effect is known for PEO of Al–Si alloys as the inheritance of chemical inhomogeneity in the oxide layer from Si-particles of silumin [ 50 ]. Fig.…”
“…Generally, from the literature, the homogeneity in the distribution of the elements in the PEO coatings is related to the microstructure of the substrate and to the electrical parameters employed during the treatment. In detail, an increase in the silicon content in the coating was observed near the zones of the substrate enriched in silicon 40 . Moreover, an increase in the duty cycle or the use of direct current produced an increase in the inhomogeneity of silicon into the coating 45 .…”
Section: Resultsmentioning
confidence: 89%
“…Considering Al-Si alloys, Krishtal et al . 40 found that an inhomogeneous distribution of Si in the substrate produced an inhomogeneous distribution of Si into the PEO layer; Li et al . 41 found that a reduction in the size of the eutectic Si causes the formation of a thicker PEO layer; Wu et al .…”
In this work, plasma electrolytic oxidation (PEO) process was applied on AlSi10Mg samples, produced with laser powder bed fusion (L-PBF), in the as printed condition and after different heat treatments, and, for comparison, on as-cast samples of AlSi10Mg. PEO process was performed in direct-current mode using high current densities and short time in a basic silicate electrolyte. For the first time, the effects of silicon morphology in L-PBF AlSi10Mg samples, in as printed condition and after different heat treatments, on the obtained PEO coating were investigated in terms of microstructure and corrosion properties. The microstructure of the substrate was characterized with optical and electron microscopy observations (optical microscopy OM, scanning electron microscopy SEM, and transmission electron microscopy TEM) and with X-ray diffraction (XRD). The analysis showed that heat treatments of annealing and solution treating modified the morphology and distribution of silicon in the samples obtained through L-PBF. The PEO coated samples were characterized with SEM, both on the surface and in the cross-section, and compositional analysis were performed with energy dispersive spectroscopy (EDS) analysis and elemental mapping. The coatings were also analyzed with XRD and the corrosion properties evaluated through electrochemical impedance spectroscopy (EIS) tests. Also microhardness tests were performed on the substrates and on the coatings. The microstructure of the coatings was strongly influenced by the silicon distribution. In particular, a non-uniform distribution of silicon and the presence of iron-rich intermetallic (obtained in the as-cast and solution treated samples) induced the formation of more porous and thinner coatings in comparison with the ones obtained in the as printed and annealed samples. The not-uniform silicon distribution produced a not-homogenous distribution of silicon into the coatings. The particular cellular structure of the as printed sample induced the formation of a coating with a higher amorphous fraction, in comparison with the ones produced on the other samples. The higher thickness and lower porosity of the coatings obtained on the annealed and as printed samples resulted in an increase of the corrosion resistance.
“…The authors of [20,21] before oxidation subjected alloys containing more than 3% of silicon before oxi dation to thermal treatment. By studying coatings and the support itself using a scanning electron micro scope, while concluded that such treatment results in an increase in the dimensions of silicon crystals.…”
This work presents the results of studying the electrochemical microplasma formation of coatings based on the AK21 alloy of hypereutectic composition in silicate-alkali electrolyte. It is found that the boundary size of primary silicon inclusion in the alloy and additional cathodic surface treatment affect sig nificantly the shape of voltage chronograms and growth dynamics of the coating thickness. It is shown that thick (more than 180 μm) layered coatings with a mosaic inner layer structure formed by fragments on the basis of the aluminum forms (amorphous Al(OH) 3 , α , δ , γ Al 2 O 3 ) in the matrix of amorphous SiO 2 are formed on this alloy at all the applied treatment modes and silicon crystal sizes. It is found that the coating inner layer structure is regularly related to the limiting dimensions of primary silicon crystals. In addition, introduction of an additional cathodic component in the high voltage polarization modes of the electrolytecoating-alloy system yielded a pronounced positive effect in the pattern of inner layer microhardness distri bution that also characteristically depends on the limiting dimensions of primary silicon crystals in the initial samples.
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