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Studies on AC Anodizing of Aluminum in Sulfuric Acid Electrolyte Containing Sodium Sulfate

ShanmugaSigamani, PR. Thangavelu, K N Srinivasan, M.Selvam

Anodizing is an electrolytic oxidation process. Good amount of work has been carried out in various electrolytes using direct current (DC). Anodizing may be regarded as the artificial thickening of the thin (1–5 nm) native oxide film that is always present on aluminum exposed to the atmosphere. In this investigation, a porous oxide coating has been formed on aluminum by using alternating current (AC) anodizing under a current density range of 1–5 A/dm2 and temperature of 15–350C in sulfuric acid electrolyte containing sodium sulfate. There is an increasing trend on the coating ratio up to 3 A/dm2. Anodizing time has some effect both on coating ratio and on anodic film thickness. Similarly, temperature of the electrolyte greatly affects both thickness and coating ratio. Increasing electrolyte temperature decreases both thickness and coating ratio. Addition of sodium lauryl sulfate (SLS) to the AC anodizing electrolyte improves the coating ratio even up to the current density of 5 A/dm2. When compared with plain bath addition of gelatin along with SLS improves the finish of the anodic coating as well as coating ratio. In AC anodizing, gelatin slightly improves the finish of the anodic coating; moreover, due to its inhibiting action on the surface gelatin reduces the dissolution of anodic coating thereby slightly improves both thickness and coating ratio compared with plain bath.