Coating of Aluminum Alloys by Micro Arc Oxidation in Nitrate Salt

TL;DR

This study explores a novel plasma electrolytic oxidation method in nitrate molten salt for coating aluminum 1050 alloys, producing a contaminant-free, two-layer oxide with enhanced properties.

Contribution

It introduces an alternative PEO process in nitrate salt, expanding coating techniques beyond aqueous electrolytes for aluminum alloys.

Findings

Coating has a two-layer structure with specific thicknesses.

The coating contains corundum and gamma and theta Al2O3 phases.

The process produces contaminant-free oxide layers.

Abstract

Plasma electrolytic oxidation (PEO) is a process for obtaining oxide coatings on valve metals. Mostly PEO is done in an aqueous solution electrolyte which limits the size of treated parts due to the system heating up. In presented work an alternative method of PEO processing applied in aluminum 1050 alloy in nitrate molten salt was investigated. The morphology, phase and chemical compositions, micro-hardness, and corrosion resistance were examined using. The obtained results showed that formed coating contains from two sub-layers, outer soft layer with the thickness of 4 micrometer and inner, denser layer with the thickness of 5 micrometer. The formed coating consists of corundum, {\gamma} - Al2O3, {\theta} - Al2O3 and is free of any contaminants originated from the electrolyte.