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Author: search.filters.author.Kumar, H.Subject: search.filters.subject.Welds

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    A Bottom-Up Optimization Approach for Friction Stir Welding Parameters of Dissimilar AA2024-T351 and AA7075-T651 Alloys
    (Springer New York LLC barbara.b.bertram@gsk.com, 2017) Anil Kumar, K.S.; Murigendrappa, S.M.; Kumar, H.
    In the present study, optimum friction stir weld parameters such as plunge depth, tool rotation speed and traverse speed for butt weld of dissimilar aluminum alloy plates, typically 2024-T351 and 7075-T651, are investigated using a bottom-up approach. In the approach, optimum FSW parameters are achieved by varying any one parameter for every trial while remaining parameters are kept constant. The specimens are extracted from the friction stir-welded plates for studying the tensile, hardness and microstructure properties. Optimum friction stir weld individual parameters are selected based on the highest ultimate tensile strength of the friction stir-welded butt joint specimens produced by varying in each case one parameter and keeping the other two constant. The microstructure samples were investigated for presence of defects, grain refinement at the weld nugget (WN), bonding between the two materials and interface of WN, TMAZ (thermomechanically affected zone) of both advancing and retreating sides of the dissimilar joints using optical microscopy and scanning electron microscopy analyses. In the experimental investigations, the optimum FSW parameters such as plunge depth, 6.2 mm, rotation speed, 650 rpm and traverse speed of 150 mm/min result in ultimate tensile strength, 435 MPa, yield strength, 290 MPa, weld joint efficiency, 92% and maximum elongation, 13%. The microstructure of optimized sample in the WN region revealed alternate lamellae material flow pattern with better metallurgical properties, defect free and very fine equiaxed grain size of about 3-5 µm. © 2017, ASM International.
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    Experimental investigation on effects of varying volume fractions of SiC nanoparticle reinforcement on microstructure and mechanical properties in friction-stir-welded dissimilar joints of AA2024-T351 and AA7075-T651
    (Cambridge University Press, 2019) Anil Kumar, K.S.; Murigendrappa, S.M.; Kumar, H.
    Effects of varying volume fractions of SiC nanoparticle (SiC NP ) reinforcement on microstructure and mechanical properties of dissimilar AA2024-T351 and AA7075-T651 joints by friction stir welding (FSW) have been investigated experimentally. A rectangular section edge groove was prepared at the adjoining surfaces of the two plates with the butt configuration before FSW. Initially, four fractional volumes with 0, 5, 8, and 13% of SiC NP are reinforced into the grooves of width, 0, 0.2, 0.3, and 0.5 mm and the FSW was performed with the first and second pass to obtain metal matrix nanocomposite (MMNC) at the weld nugget zone (WNZ). The characterization of microstructure specimens was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The FSW joint specimen produced with 5 vol% fraction of SiC NP for second pass processing observes a defect-free, homogeneous distribution of SiC NP with a mean grain size of about 2-3 ?m at the WNZ and weld joints higher in tensile strength, 411 MPa, yield strength, 252 MPa, and percentage elongation, 14.3. The result shows that varying volume fractions (5, 8, 13%) of the SiC NP after the FSW second pass led to significant grain refinement at the WNZ and higher mechanical properties compared with FSW specimens prepared without SiC NP . Higher hardness of 150 Hv was observed in the WNZ for specimen produced with 13 vol% fraction SiC NP . © Materials Research Society 2019.
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    Comparative study of diode laser welding of solid-solution/precipitation-strengthened Fe-Ni-Cr-based superalloys
    (Taylor and Francis Ltd., 2025) Kumar, H.; Banerjee, K.; Aqeel, M.; Shariff, S.M.
    This study investigates autogenous diode laser welding of two differently strengthened Fe-Ni-Cr superalloys: solid-solution strengthened Incoloy 800 and precipitation-strengthened Incoloy A286. Effects of laser power, welding speed, and defocusing distance on weld bead geometry, microstructure, and mechanical properties were comprehensively analyzed. Butt weld joints produced with optimum and similar heat input conditions achieved joint efficiencies comparable to their base metals. Microstructural analysis of fusion zone revealed columnar dendrites of ?-(Ni,Fe) in both alloys, with A286 showing segregation of Ti, Cr, and Mo intermetallics at interdendritic regions, while Incoloy 800 exhibited refined columnar/equiaxed dendrites with chromium carbides and Fe-Ni-Ti intermetallics. Mechanical testing indicated enhanced yield strength but reduced impact toughness and marginal hardness gain in A286 welds, whereas Incoloy 800 welds maintained similar hardness to the base material. Overall, the study demonstrated utilization of fiber-coupled diode laser welding for producing butt-joints in both superalloys, supporting their potential adoption in high-temperature applications. © 2025 Taylor & Francis Group, LLC.