Varying rotational speeds and their effect on the mechanical properties of friction stir welded 6082-T651 aluminium alloy plates

Abstract

The need to understand the effects of varying rotational speeds on the mechanical properties of Friction Stir Welded 6082-T6 aluminium alloy plates motivated this study. The rotational speeds used were influenced by the capabilities of the Friction Stir Welding machine used. The lowest rotational speed used on the machine was 680 rpm followed by 780 rpm and 900 rpm respectively. The rotational speed is the rate at which the welding tool rotates around its axis and is one of the most important parameters in Friction Stir Welding. Speeds are related to processing temperature which influences the underlying physical conditions of the material. The changes in rotational speeds had an influence on the resulting mechanical properties. The change in rotational speed affected heat distribution in the weld area causing changes in the ductility of the Heat Affected Zone (HAZ) which affected weld behavior during mechanical testing and how these failed during testing. The optimal welding rotational speed was obtained during the welding of 6082-T6 aluminium alloy plates used in this study. This observation is also backed by mechanical evaluation done on friction stir welded plates used and results compares to work of other researchers in the field. In terms of hardness, in the weld area, the optimum speed had a higher average hardness distribution in the weld area. Heat distribution in the weld area caused changes in the ductility of the Heat Affected Zone (HAZ) and this was proven during tensile testing. Vickers hardness across the weld area revealed changes in the hardness of the base metal and the weld area. Changes in tensile strength due to changes in rotational speed are also documented and reported on. The plunge depth, tilt angle and welding speed were kept constant throughout the duration of the welding procedure. This made it easier to analyze and compare the resulting changes in the properties of Friction Stir Welded 6082-T651 aluminum alloy plates.