The heat-affected zone (HAZ) is common to all welding processes.Although the term TMAZ technically refers to the entire deformed region, it is often used to describe any region not already covered by the terms stir zone and flow arm. Unlike the stir zone, the micro-structure is recognizably that of the parent material, albeit significantly deformed and rotated. In this region the strain and temperature are lower and the effect of welding on the micro-structure is correspondingly smaller. The thermo-mechanically affected zone (TMAZ) occurs on either side of the stir zone.The flow arm zone is on the upper surface of the weld and consists of material that is dragged by the shoulder from the retreating side of the weld, around the rear of the tool, and deposited on the advancing side.The precise origin of these rings has not been firmly established, although variations in particle number density, grain size and texture have all been suggested. A unique feature of the stir zone is the common occurrence of several concentric rings, which has been referred to as an "onion-ring" structure. The grains within the stir zone are roughly equiaxed and often an order of magnitude smaller than the grains in the parent material. The stir zone (also known as the dynamically recrystallised zone) is a region of heavily deformed material that roughly corresponds to the location of the pin during welding.The micro-structure can be broken up into the following zones: The solid-state nature of the FSW process, combined with its unusual tool shape and asymmetric speed profile, results in a highly characteristic micro-structure. This process of the tool traversing along the weld line in a plasticised tubular shaft of metal results in severe solid-state deformation involving dynamic recrystallization of the base material. As the tool is moved forward, a special profile on the probe forces plasticised material from the leading face to the rear, where the high forces assist in a forged consolidation of the weld. This heat, along with that generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without melting. įrictional heat is generated between the wear-resistant tool and the work pieces. After a short dwell time, the tool is moved forward along the joint line at the pre-set welding speed. The probe is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface.
During welding the tool is fed into a butt joint between two clamped workpieces, until the probe pierces into the workpiece and shoulder touches the surface of the workpieces. The FSW is performed with a rotating cylindrical tool which has profiled pin (also known a probe) having diameter smaller than the diameter of shoulder. The progress of the tool through the joint, also showing the weld zone and the region affected by the tool shoulder TWI held patents on the process, the first being the most descriptive. It was invented and experimentally proven at The Welding Institute (TWI) in the UK in December 1991. Application of FSW can be found in modern shipbuilding, trains, and aerospace applications. In addition, joining of dissimilar metals, such as aluminium to magnesium alloys, has been recently achieved by FSW. More recently, it was successfully used in welding of polymers. FSW is capable of joining aluminium alloys, copper alloys, titanium alloys, mild steel, stainless steel and magnesium alloys. It is primarily used on wrought or extruded aluminium and particularly for structures which need very high weld strength. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough. Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. Friction stir welding ( FSW) is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material.
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