COMPARISION OF CORROSION BEHAVIOUR OF ULTRASONICALLY PROCESSED AND CONVENTIONALLY CAST AZ9I ALLOYS

Abstract

Ultrasonic processing of magnesium alloys during casting leads to considerable refinement in its grain size. It leads to considerable improvement in mechanical properties as well. 1-lowever, limited information is available on corrosion behavior of ultrasonically treated and refined magnesium alloys. In this work, AZ91 alloy is investigated for its corrosion behaviour after processing it ultrasonically. Ultrasonic processing of casting during solidification led to fine grained structure as compared to conventionally cast AZ91 alloy. The materials were characterized using SEM/FESEM, EDS, XRD and optical microscope. Electrochernical methods and immersion tests have been used for corrosion investigations. The corrosion rate of ultrasonically processed AZ91 alloy decreased considerably as compared to conventionally cast AZ91 alloy. Thus a comparison has been made between corrosion behaviour of ultrasonically cast and conventionally cast AZ91 alloy. The improved corrosion resistance of ultrasonically processed AZ91 alloy over conventionally cast AZ91 alloy is attributed to formation of continuous and protective oxide film over l- phase. This was possible because of reduced inter-particle distance between 1- phase particles caused by grain refinement. This oxide film has higher stability because of higher aluminum content and acts as a protective barrier to limit corrosion attack.