Galvanostatic Anodizing of Additive Manufactured Al-Si10-Mg Alloy

Abstract

The galvanostatic anodizing behavior of additive manufactured (AM) Al-Si10-Mg alloy was studied in H2SO4 electrolyte. The analysis of the voltage vs time response was complemented with a systematic characterization of the anodic oxide layer using a variety of techniques. In addition, a cast alloy of approximately the same chemical composition as that of the AM specimens was used as a reference in this study. Significant differences were found in the voltage-time characteristics of the samples analyzed. Besides, an anisotropic anodizing behavior was observed in the additive manufactured specimens. Due to the fine silicon microstructure present in the additive manufactured samples, the anodic oxide growth was much more obstructed than for the cast alloy. Nevertheless, even though the oxide layer was generally thinner in the AM samples for the same conditions and anodizing time, a much more continuous and uniform oxide layer was found in the additive manufactured specimens compared to the cast alloy. The porous structure was found to be greatly affected by the fine distribution of the silicon phase in the AM parts.

Effect of Heat Treatments on the Anodizing Behavior of Additive Manufactured AlSi10Mg

“…They could indicate that a very small fraction of the material remains unoxidized but are thought to result from the polishing procedure. Regardless, for a NHT specimen most of the silicon in the oxide layer is oxidized as has been recently demonstrated by XPS analysis 17 . The border between oxide layer and unoxidized material has an irregular appearance.…”

“…The AM specimens show a much larger transition region than the cast alloy. Previous research 17 on NHT specimens has pointed out that the time interval of the transition region corresponds with the time required to oxidize one cell. A similar behavior is now found for the stress released specimens.…”

“…Anodizing or anodic oxidation is an electrolytic process that enables the production of much thicker oxide coating, improving properties like abrasion resistance, electrical insulation, adhesion and corrosion resistance 15 . Previous research 16,17 has pointed out that additive manufactured and cast alloy material shows different anodizing behavior. Higher anodizing voltages, lower oxide growth rates and a smoother oxide film were obtained for the additive manufactured specimens.…”

“…These differences were found to depend on the distribution of silicon, the cast alloy having large dendritic structures while the AM specimen has a fine distribution in a 3D network 16 . During anodizing, the silicon of the AM materials is completely oxidized, unlike the silicon in the cast alloy which is only superficially oxidized 17 . This is related to the size of the silicon inclusions.…”

Influence of Si Content on the Microstructure and Corrosion Behavior of Additive Manufactured Al-Si Alloys

“…Several Al-Si alloys are nowadays available as spherical metal powder and largely, in terms of volume production, processed by additive manufacturing [9]. The microstructure of additive manufactured (AM) Al-Si alloys has been described in a number of studies [10][11][12][13][14][15][16][17]. The untreated specimens present a very fine distribution of silicon, forming a 3-dimensional network that encapsulates the aluminium phase in very small cells.…”