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Microstructure and mechanical properties of L415/N08825 bimetallic composite pipe welded joint using GTAW + SMAW

100%

Wang L. , Wu D. , Xu M. , Hu Y. , Zhou P.

tom Vol. 23, no. 1

art. no. e18, 2023

The L415/N08825 bimetallic composite pipe welded joint was produced by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) using nickel superalloy Inconel 6625 filler. The dendritic austenite grows in the direction perpendicular to the fusion line in the weld metal. The main elements, such as Cr, Ni, Mo and Fe show a large concentration gradient in the interface of the HAZ and weld metal. The unmixed zone in the three-phase zone is because of the differences in thermo-physics properties. The yield strength and tensile strength are 432 and 582 MPa, respectively. The interface between the cladding layer and the base layer fracture first, then the cladding layer, and the base layer finally. Compared with the impact toughness of the weld metal, the HAZ has a better impact toughness. Moreover, the average hardness of the weld is higher than that of the base metal and the HAZ. After welding, the HAZ is softened, and the hardness of the fusion line is higher than that of the base metal. The mechanical properties of the welded joint meet the standard requirements and it is advisable to use the GTAW + SMAW process for the welding of L415/N08825 bimetallic composite pipe.

Research on Distribution and Morphology of Primary Si Under the Effect of Direct Current

100%

Li J. , Njuguna B. K. , Ni P. , Wang L. , Tan Y.

tom Vol. 66, iss. 2

367--372

A source of pure silicon was added into an alloy refining system during a refining process with the application of a direct electric current. The effect of the temperature difference between the graphite electrodes and the alloy was decreased. The temperature increase value (ΔT) of the Al-28.51wt.%Si alloy sample caused by Joule heating was calculated by weighing the mass of primary silicon. When the current density was 5.0×105A/m2, the overall temperature increase in the alloy was about 90°C regardless of the alloy composition. Adequate silicon atoms recorded the footprint of the electric current in the alloy melt. The flow convection generated by the electric current in the melt during the solidification process resulted in the refinement of primary silicon. The Fe impurity content in alloy refining without the electric current density was 2.16 ppm. However, it decreased to 1.27 ppmw with the application of an electric current density of 5.0×105A/m2.