Effect of repetitive corrugation and straightening on the microstructure and mechanical properties of al li alloy and study of its thermal stability

Abstract

In this research work, Repetitive Corrugation and Straightening (RCS), a Severe Plastic Deformation (SPD) technique was employed for producing Ultrafine grain structure in AA 8090 Al-Li alloy. AA8090 alloy sheet was corrugated and straightened continuously up to the maximum number of passes till the failure of the specimen occurred. Different corrugation profiles, namely, a semi-circular die (radius 10 mm), a flat groove die (flank distance 5 mm, flank height 3 mm and corrugating angle 30o) and a V-groove die (pitch 20 mm, corrugating angle 30o and curve radius 2 mm) were used for the investigation of influence of die profiles on the severe strain imparted on the specimen and the grain refinement. The process was carried out at the isothermal condition (T=300°C), with three different pressing velocities of 1.5 mm.s-1, 2 mm.s-1 and 2.5 mm.s-1. The strain imparted in the specimen was found using the Optical Grid Analysis method. Grain refinement was studied from the microstructure examination using Electron Backscattered Diffraction (EBSD) analysis. The grain size distribution and misorientation of grain boundaries were studied using the EBSD data. Mechanical properties, namely hardness, yield strength and ultimate tensile strength were studied and relationship between the microstructure and the mechanical properties have been established. The study reveals the enabling of maximum strength by the corrugated die with v-groove profile, at lower pressing velocity (i.e. at 1.5 mm.s-1), after eight number of passes. At this stage, the material had an average grain size of 2 and#956;m, with a grain size distribution that ranges from 200 nm - 8 microns. newline