Material Flow and the Shear Layer in the Upper Weld Zone during Friction Stir Welding of Aluminium Alloys

Abstract

Friction stir welding (FSW) experiments were conducted using three different aluminium alloys (a work hardened alloy, an age hardened alloy and a cast alloy) followed by metallographic examination focusing on the upper weld zone and the surface layer. The examination has revealed the features of the major forward flow resulting from the forward motion of the tool shoulder. A thin shear layer due to tool rotation was identified between the tool shoulder and the workpiece with a distinctive shear flow direction . The thickness of the shear layer was alloy dependent. An embedded layer in the upper weld zone has also been identified. The flow phenomena leading to this will be discussed. A velocity profile in the shear layer, based on the apparent alignment of Si particles in the cast alloy after welding, has suggested a dominant sliding contact condition.

An Alternative Pressure-dependent Friction Boundary Condition for Modeling Self-reacting Friction Stir Welding

“… are constants under the same welding condition. During FSW, a newly formed shear layer is established and circulates around the pin for a short distance to the trailing side until it deposits [4]. This is defined as one wear cycle, which happens every tool revolution.…”

“…Figure2(a) Top view of shear layer in FSW[31], (b) shear layer behind the pin in FSW[5], (c) schematic illustration of shear layer around the pin[4] …”

An alternative pressure-dependent velocity boundary condition for modeling self-reacting friction stir welding

“…Recognizing the importance of understanding the weld formation mechanism during FSW/SRFSW, various researches have been taken to investigate the experimentally observed shear layer [3][4][5] formed in the process. As a result of the interactions between the tool and the workpiece, localized shear develops in the tool vicinity and forms a narrow region of intense plastic deformation, i.e., shear layer, which is also referred to as shear band [6,7].…”

Flow, process forces and strains during Friction Stir Welding: A comprehensive First principle approach

“…Friction stir welding (FSW) has proved out to be a breakthrough for joining technology, being able to weld dissimilar and relatively difficult-to-weld materials effectively and efficiently. The eminent advance of FSW has attracted the interest of numerous researchers who have investigated the material flow, 1–6 process forces 7,8 and thermal evolution 9–13 during the FSW process. These areas of investigation are largely based upon experimental methods employed to reveal the material flow behaviour; and computer-based modelling techniques used for the thermal and load analyses.…”