A Study of the Environment–Friendly Chrome-Free Chemical Conversion Coating on 2024 Aluminium Alloy

Abstract

In order to develop an environment-friendly method of forming a chemical conversion coating on 2024 aluminium alloy surface without the toxic hexavalent chromium compounds, in this paper a process with sodium molybdate and potassium permanganate as the main compositions of the treating bath has been investigated. Solution composition and process parameters have been optimized. The chemical conversion coating has good corrosion resistance, evaluated with dropping test. Micro-structure and components of the conversion coating have been studied by various micro-analysis methods, and the growth mechanism of the chemical conversion coating has also been investigated.

The study on performances of environment-friendly colorless chemical conversion coatings on aluminum alloy

“…And, hexavalent chromium is harmful to human skin, respiratory tract, digestive system and kidney. The IOP Publishing doi:10.1088/1742-6596/2539/1/012049 2 treatment of wastewater from the chromate chemical conversion process is complicated, which is harmful to the ecological environment [4].…”

“…The environment-friendly chemical conversion process does not use hexavalent chromium compounds but often uses titanium/zirconium salts [5][6][7], molybdate [8,9], rare earth salts [10,11], cobalt salts [12], organic silane [13], trivalent chromium salts [14][15][16]. Some conversion coating can be prepared to be colorless.…”

Composition and Performance of Nanostructured Zirconium Titanium Conversion Coating on Aluminum‐Magnesium Alloys

“…Chemical conversion film is formed to oxidize the surface layer into the metal oxide layer [8]. Chromate treatment, including phosphate-chromate method, acid chromate method, and alkaline chromate method, is the concernful treatment method for chemical conversion [9][10][11][12]. Acid chromate treatment is more widely used in the actual application [13]; due to that, the films formed via alkaline chromate treatment are soft, loose, and vulnerable to scratches.…”