Oxide Layer Formation on Al-Si-Zr Alloy using Anodizing process

Abstract

Anodizing is a process for producing decorative and protective films on articles made from aluminium and its alloys. It is essentially the process of producing the film of aluminium oxide which forms on aluminium when direct current at sufficient voltage is passed through a suitable electrolyte in which the aluminium is the anode and a suitable material is cathode. By far the largest amount of anodizing is carried out in an electrolyte consisting of sulphuric acid dissolved in water. For some special aircraft requirements chromic acid solutions are used, whilst oxalic acid anodizing was used widely for many years, particularly in Germany and Japan, and still find limited application. Phosphoric acid anodizing has been used as a basis for plating but now the use of zincate immersion deposit processes is general practice. Other specialized electrolytes or mixtures of electrolytes have found limited fields of application. One of the most important of these is the use of sodium ammonium borate or ammonium phosphate electrolytes for electrolytic condensers.