<p>Al-Li-Cu alloy Al2195-T84 is used extensively in the aerospace launch vehicle’s external fuel tank structures. Aerospace components are generally joined using aluminium alloy materials, which increases the overall payload capacity of the launch vehicle. In this context, friction stir welding (FSW) process could be a potential solution. In this research work, Al2900-T6 specimens hot extruded were welded by FSW, using different parametric combinations of tool rotation and welding speed. The friction-stir weldments were further subjected to deep cryogenic treatment. Microstructure and some mechanical properties of the weldments were investigated for both cryo-treated and untreated conditions. It was observed that the grain size of the nugget zone (NZ) got refined after the cryogenic treatment. It was also revealed that microhardness was more in case of cryo-treated joints as compared to untreated. Micro-hardness of the NZ was observed to be highest due to formation of finer grains after exposure to cryogenic temperature. Deep cryogenic treatment has also improved impact toughness and tensile properties such as yield strength and % elongation of the FSW joints. The strength of FSW joint is significantly affected by rotational and translational speed of the tool. FSW weldments were fabricated using several combinations of the welding speed (10–50 mm/min) and tool rotation (800–2000 rpm).&nbsp; In the present study, three levels for tool rotation (1000, 1150, and 1300 rpm) and two levels for welding speed (26, 30 mm/min) have been considered. Different types of tools were used in the recent past for producing FSW joint. In the present work, conventional tapered cylindrical type tool was used for FSW. The material of the tool was EN-32 steel, which is case-hardened steel with low tensile strength. The FSW process was carried out using a modified vertical milling machine.&nbsp; The specimens were placed in square butt joint configuration and were held firmly in the position, without any gap between faying surfaces using a specially fabricated fixture. Friction stir welding was performed parallel to plate extrusion direction. The cross-sectional stereo micrographs of the weldments were taken using inverted optical microscope (Dewinter microscope, Bangalore) to analyze the various zones of the weldments. Further, the weldments were sectioned, mounted and polished for hardness, tension and impact toughness test as per ASTM E384-17, ASTM E-8 and ASTM E23-18 standards respectively. A digital micro Vickers hardness tester (RMHT-201 by Radical Scientific Equipments Pvt. Ltd., India) was used to measure the microhardness of the different zones of weldments. A load of 1000 g was applied for a dwell time of 20 s for the measurement of hardness. The distance between the two indentations was taken as 0.5 mm, while moving across the weld, for a particular point, average of five readings (along the weld) were taken. The entire specimen prepared from the weldments using different parametric combinations were further subjected to deep cryogenic treatment (DCT). The well accepted 2-8-2 DCT cycle was used for the treatment. During the DCT treatment, the temperature of cryogenic chamber was lowered down from atmospheric temperature (300 K) to 88 K in 2 h. The samples were soaked at 88 K for 8 h. The temperature of cryogenic chamber was then ramped up from 88 K to atmospheric temperature (300 K) in another 2 h as per the cryogenic cycle. The cryogenic treated and untreated specimens were analyzed with respect to the above said metallurgical and mechanical properties.</p>

Influence of In-Process Cryogenic Cooling on Mechanical Performance of Friction Stir T6 â€“ AA 2900 Alloy Weldments of Cryogenic Treatment on Mechanical Performance of Friction Stir T6 - Aa 2900 Alloy Weldments

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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