Friction Stir Welding (FSW) of Aged CuCrZr Alloy Plates
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INTRODUCTION
FRICTION stir welding (FSW) is a solid-state joining process invented by The Welding Institute (TWI), UK.[1] This process facilitates joining of similar and dissimilar materials, which are otherwise difficult to weld by fusion welding techniques.[2–6] This process is free of pollutants like fumes, fluxes, and slag, and eliminates many problems associated with the fusion welding, such as inclusions, porosity, micro- and macrosegregation, grain coarsening in the fusion zone, and the HAZ. This process was developed initially for aluminum alloys; however, it has evolved substantially over the years and has become suitable for joining of a large number of materials.[7–16] In addition to the experimental studies on the different aspects of the FSW process and the resulting weld joints, substantial amount of work has been devoted for process modeling
KAUSHAL JHA and G.K. DEY are with the Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, Maharashtra, India and also with the Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, Maharashtra, India. Contact e-mail: [email protected] SANTOSH KUMAR and K. NACHIKET are with the Bhabha Atomic Research Centre. K. BHANUMURTHY is with the Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, Maharashtra, India. Manuscript submitted July 5, 2017. Article published online November 20, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
and simulation for computation of the resulting thermal field and flow field.[17–21] Copper and its alloys are technologically important materials primarily because of their high thermal and electrical conductivities. Very high thermal conductivity of copper and several of its alloys permits efficient heat removal. Welding of copper is generally difficult by conventional fusion welding processes because of its high thermal diffusivity. Thermal conductivity of copper is nearly thrice than that of aluminum. Therefore, the heat-input requirement for melting the metal is very high. During arc welding, they are also susceptible to embrittlement of the weld joint. Oxygen gets dissolved in liquid metal and subsequently segregates at the grain boundaries during solidification, leading to embrittlement. In precipitation-hardened alloys, oxygen can combine with the other alloying elements in the melt pool, and this may compromise the strength of the joint. These problems associated with welding of copper and its alloys can be largely overcome by employing FSW. For this reason, substantial study has been performed on friction stir welding (FSW) and friction stir processing (FSP) of Cu and its alloys.[22–30] Lee et al.[22] have reported production of sound weld joint between Cu plates of 4-mm thickness by FSW at a tool-rotation speed of 1250 rpm and a tool traverse speed of 61 mm/min. They have reported that the joint exhibited 87 pct tensile strength compared with the
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parent metal and attributed the loss of strength to the annealing effects. Polar et al.[23] have reported thermal cycle, microstructural attrib
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