CORROSION BEHAVIOU R OF ULTRAFINE GRAINED AL ALLOYS

Abstract

For the production of bulk ultrafine grained (UFCi) materials with homogeneous and equiaxed microstructures whose average grain sizes I tni various techniques are employed. However, using some of these techniques it is difficult to obtain large samples with UFG structure. Many have worked on multiaxial forging technique at room temperature as well as at high temperatures but none had performed this work on cryogenic temperature (appro. 77k). The present work is to do multiaxial forging at lower temperature i.e. cryogenic temperature so as to suppress the dynamic recovery during deformation. Multiaxial Cryoforging (MACF) is characterized by higher deformation rates in order to produce bulk samples. 'l'hese factors along with the severity of deformation are expected to influence the microstructure evolution, mechanical properties and corrosion properties of MACF material. Aluminium 6082 alloy also known as structural alloy: is a medium strength alloy having high strength to weight ratio. In the first part of the work, the solution treated Al 6082 alloy was subjected to MACF at different conditions to true strain of 1.8, 3.6 and 5.4. It's effects on microstructure and mechanical properties were investigated by hardness tests, tensile tests, optical microscopy and TEM. A substantial improvement in the strength has been observed in MACF material as compared to solution treated Al 6082 alloy. In the second part of the work, the electrochemicat behavior of MACF 6082 alloy was compared to solution treated 6082 alloy by using open circuit potential (OCP) and Tafel Extrapolation Polarization. A small decrease in corrosion resistance of the MACF material as compared to solution treated Al 6082 alloy was observed.