Fig. 1 — Different pin profiles used in FSW. particles throughout the matrix. Eccentricity of the rotating object is related to the dynamic orbit due to eccentricity. Khodaverdizadeh et al. (Ref. 9) considered TH and SQ pin profiles. They reported that the SQ pin profile has a finer grain structure, generates higher peak temperature, and higher hardness values. In addition, higher heat generation due to plastic deformation and smaller interfacial contact area with the workpiece leads to lower frictional heat generation relative to the TH pin. Palanivel et al. (Ref. 10) considered straight (SQ, HEX, octagon (OCT)) and taper (SQ and OCT) pin profiles. They found that the joint fabricated using the straight SQ pin profile yielded highest strength of 273 MPa and tool rotational speed of 950 rev/min. Fujii et al. (Ref. 11) considered the SC, TH, and TR pin profiles. They reported that in the case of the 1050-H24 aluminum alloy, SC produces a weld with the best mechanical properties. For 6061-T6, the tool shape does not significantly affect the microstructures and mechanical properties of the joints. For 5083-O, at a high rotation speed (1500 rev/min), the TR is the best; at the middle rotation speed (800 rev/min), the TH is the best; while for a low rotation speed (600 rev/min), the tool shape does not significantly affect the microstructures and mechanical properties of the joints. Vijay and Murugan (Ref. 12) considered three straight (S) and taper (T) SQ, HEX, and OCT pin profiles. They found that for the straight SQ pin profile, it exhibited maximum tensile and joint efficiency, while the taper OCT pin profile exhibited maximum (%) elongation. A defect-free weld is obtained when the taper HEX pin and straight SQ pin tools are used for joining aluminum matrix composites (AMCs). Padmanaban and Balasubramanian (Ref. 13) considered the SC, TC, TH, TR, and SQ pin profiles. They found that the joints fabricated using the TH pin profile yielded a defectfree and fine-grained nugget region, which led to the enhancement of hardness and tensile properties of the welded joints. Gadakh and Kumar (Ref. 14) developed a process window for the AA 6061-T6 aluminum alloy and obtained a finegrained structure using the TC pin profile. Boz and Kurt (Ref. 15) considered five different pin profiles. Four are TH — with 0.85, 1.10, 1.40, and 2.0 mm pitch — and the last SQ with 5 5 mm cross section. They have found that the TH with 0.85-mm pitch exhibited maximum elongation (%) and reduction in cross-sectional area (%), and the TH with 1.10-mm pitch exhibited maximum UTS. Suresha et al. (Ref. 16) have considered TC and SQ profiles for FSW of the AA7075-T6 aluminum alloy. They reported the welded joints produced by the TC tool show better joint efficiency when compared to the SQ tool. Ramanjaneyulu et al. (Ref. 17) studied the influence of different tool pin profiles such as TC; taper (TR, SQ, PEN, and HEX) on heat generation; and microstructure of the AA2014 aluminum alloy. They have reported the rate of heat generation as well as peak temperatures are relatively higher in the case of noncircular pin profiles, increasing with the number of flats (i.e., SQ to HEX) and lowest for TC. From the reported literature, it is understood that the pin geometry plays a vital role for material flow, temperature history, grain size, and mechanical properties in the FSW process. From these aspects, a question arises why the results are varied for different tool geometries and thereby variations in properties and microstructures. With this consideration, in this paper, an analytical modeling using different tool geometries is considered to estimate the heat generated due to friction between the workpiece and tool surfaces. Many of the referred literature stated that the failure of friction stir welded joints takes place at the heat-affected zone (HAZ) where the density of the needle-shaped precipitate (’’) is less. From the proposed developed models for different tool geometries, one can find the peak temperature at the weld zone so that severe softening in the HAZ (because of the reversion of ’’ precipitates during the weld thermal cycle) can be minimized (Ref. 18) by controlling weld process parameters. WELDING RESEARCH 116-s WELDING JOURNAL / APRIL 2015, VOL. 94 Fig. 2 — Schematic of the triangular probe. Fig. 3 — Schematic of the surface orientations and infinitesimal segment areas. The top left probe side is Q2, bottom left square probe is Q3,and right shoulder surface is also seen.
Welding Journal | April 2015
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