Mechanical Behavior of Friction Stir Extruded Tubes

Abstract

Friction Stir Back Extrusion (FSBE) is a new grade of severe plastic deformation processes capable of producing metallic tubular geometries that exhibit ultrafine grain structure and superior mechanical properties. FSBE of tubular sections provide opportunities for producing lightweight rigid structures for the automotive, aerospace and construction industries. This research investigates the impact of rotational speed and feed rate on the mechanical properties, power consumption and cycle time for FSBE of Magnesium AZ31-B tubes under air cooling medium to determine the optimal settings. The investigation is conducted utilizing Response Surface Methodology (RSM) and desirability multi-response optimization technique. RSM results suggest that the ultimate tensile strength and toughness are impacted by both rotational speed and feed rate and are more sensitive to spindle rotational speed. Yet, both parameters did not show a significant statistical impact on percent elongation. The optimal settings to maximize mechanical properties and minimize production indicators are 2000 rpm and 116 mm/min. Furthermore, the effect of submerging conditions (in water at 25 °C and 2 °C) on the grain size and mechanical properties was investigated and compared to FSBE in air. It is shown that the impact of submerging is statistically insignificant in terms of the mechanical properties of the produced tubes. On the other hand, finer grains were observed at the inner wall of the tube for FSBE in air and underwater FSBE at 25 °C when compared to underwater FSBE at 2 °C.