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Effect of Nitric and Oxalic Acid Addition on Hard Anodizing of AlCu4Mg1 in Sulphuric Acid

1
Lockwitzgrund 123a, D-01731 Kreischa, Germany
2
Materials and Surface Engineering Group, Chemnitz University of Technology, D-09107 Chemnitz, Germany
*
Author to whom correspondence should be addressed.
Metals 2018, 8(2), 139; https://doi.org/10.3390/met8020139
Received: 15 December 2017 / Revised: 7 February 2018 / Accepted: 13 February 2018 / Published: 17 February 2018
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Abstract

The anodic oxidation process is an established means for the improvement of the wear and corrosion resistance of high-strength aluminum alloys. For high-strength aluminum-copper alloys of the 2000 series, both the current efficiency of the anodic oxidation process and the hardness of the oxide coatings are significantly reduced in comparison to unalloyed substrates. With regard to this challenge, recent investigations have indicated a beneficial effect of nitric acid addition to the commonly used sulphuric acid electrolytes both in terms of coating properties and process efficiency. The present work investigates the anodic oxidation of the AlCu4Mg1 alloy in a sulphuric acid electrolyte with additions of nitric acid as well as oxalic acid as a reference in a full-factorial design of experiments (DOE). The effect of the electrolyte composition on process efficiency, coating thickness and hardness is established by using response functions. A mechanism for the participation of the nitric acid additive during the oxide formation is proposed. The statistical significance of the results is assessed by an analysis of variance (ANOVA). Eventually, scratch testing is applied in order to evaluate the failure mechanisms and the abrasion resistance of the obtained conversion coatings. View Full-Text
Keywords: anodic oxidation; additives; aluminum alloy AlCu4Mg1; nitric acid; oxalic acid; hardness; porosity; energy efficiency; scratch resistance anodic oxidation; additives; aluminum alloy AlCu4Mg1; nitric acid; oxalic acid; hardness; porosity; energy efficiency; scratch resistance
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Sieber, M.; Morgenstern, R.; Scharf, I.; Lampke, T. Effect of Nitric and Oxalic Acid Addition on Hard Anodizing of AlCu4Mg1 in Sulphuric Acid. Metals 2018, 8, 139.

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