EFFECT OF INHOMOGENEOUS MICROSTRUCTURE ON SUPERPLASTIC FORMING CHARACTERISTICS OF Al 5086 ALLOY

Abstract

Friction Stir Processing (FSP) was the severe plastic deformation technique used for generating line grains in the through thickness of the sheet of Aluminum 5086 alloy. Multipass method of friction stir processing was adopted as it was capable of producing fine grains at bulk level which is desired for superplastic deformation. Inhornogeneous microstructures through friction stir processing were developed using four different tools with varying tool-pin heights. Friction stir processing was performed at rotational and traverse speeds of 720rpm and I 55mm/mm respectively, maintaining a tool tilt of 2°. Multipass FSP was performed on a 6mm sheets maintaining 50% overlap on the retreating side and the sheets with different fraction of coarse and line microstructures i.e. 25%, 50%, 72% and 100% line grain microstructures, in the thickness direction were produced after removing the unwanted material. Superplaslic forming was performed on the microstructurally inhomogeneous sheets, obtained through friction stir processing. Superplastic bulge forming was performed at a constant pressure of l.l0MPa and temperature of 500°C, which was continued up to height of 23.5mm. The sheet processed by 25% showed higher effective strains at the apex. The sheet which was processed 72% was showing lower thickness variation from edge to apex also the bulge shape in this condition was close to the ideal spherical profile. Microstructures from the edge to apex did not show considerable change in their processing percentages