Current Issue : October-December Volume : 2021 Issue Number : 4 Articles : 5 Articles
Aluminum alloy has been widely used due to its excellent workability, and double‐pulse metal inert gas welding (MIG) has become a popular technique in aluminum alloy welding. In this study, a cross‐complementary test was performed to study the effect of double‐pulse characteristics on weld bead formation and mechanical properties in MIG welding. The test was carried out on an AA6061 aluminum alloy using flat overlaying welding. After welding, the micro‐metallographic structure and macro‐mechanical performance of the weld bead were explored. The test results showed that the two methods of increasing the base current amplitude or the low‐frequency of the current effectively enhanced the oscillation of the molten pool, refined the grain size of the fusion zone, and improved the mechanical properties of the weld. Additionally, by comparing the macroscopic photograph of the specimen and the corresponding welding parameters in the test, the formation characteristics of the bead’s fish‐scale pattern in double‐pulse MIG welding were found when appropriate welding parameters were adopted and weld bead formation was good. This test result provides a strong scientific basis for the selection of welding parameters in the actual promotion and application of double‐pulse MIG welding....
Wire + Arc Additive Manufacture is an Additive Manufacturing process that requires a substrate to initiate the deposition process. In order to reduce material waste, build and lead time, and improve process efficiency, it is desirable to include this substrate in the final part design. This approach is a valid option only if the interface between the substrate and the deposited metal properties conform to the design specifications. The effect of substrate type on the interface microstructure in an aluminium part was investigated. Microstructure and micro-hardness measurements show the effect of substrate alloy and temper on the interface between the substrate and deposited material. Microcracks in the as-deposited condition were only found in one substrate. The deposited material hardness is always lower than the substrate hardness. However, this difference can be minimised by heat treatment and even eliminated when the substrate and wire are made of the same alloy....
This article describes the experimental studies of a preloaded asymmetric multi-bolted connection in the exploitation state. The construction of two stands were introduced: for bolt calibration and for evaluating the bolt forces in a multi-bolted connection. The bolts were tightened in a specific optimal sequence, in three passes, monitoring the force values in the bolts using a calibrated strain gauge measuring system. The studies were conducted for the selected multi-bolted connection on an Instron 8850 testing machine. The measurement data were saved in MATLAB R2018b Simulink. The measurement results were analysed statistically and are presented via charts showing the distributions of the normalised values of the bolt forces as a function of the linearly increasing and decreasing exploitation loads. We show that the forces in individual bolts, after unloading the multi-bolted connection, change in relation to the initial values of their preload....
This study investigated the microstructural evolution of the weld interface and creep fracture behavior of 10% Cr martensitic steel welds using Haynes 282 filler metal. The welded joints were subjected to post‐weld heat treatment (PWHT) at temperatures of 738 °C for 4, 8, and 15 h. Creep tests were carried out at 600 °C under stress of 200 MPa. The creep rupture life increased with an increase in holding time for PWHT up to 8 h compared to the as‐welded condition. However, when the holding time for PWHT was further increased to 15 h, creep properties (i.e., rupture life and creep strain) decreased considerably, and the failure location was found to shift from the ICHAZ to the weld interface. The microstructural investigation revealed that Type I carbides precipitated at the weld interface and recrystallized grains with Cr depletion were formed near Type I carbides in the partially mixed zone during creep exposure. The creep failure at the weld interface began on the surface and propagated inward through the recrystallized grains of the weld‐interface region....
In order to achieve the thermal structural integrity analysis of the solid rocket motor nozzle accurately and efficiently, the multifield (flow-thermal-mechanical) coupled numerical investigation was carried out based on the mesh-based parallel code coupled interface. The numerical simulation process and finite element model of the coupled algorithm and engineering algorithm were obtained, while the physical model was simplified appropriately. The coupled interface parameters, internal flow field, temperature field, and stress field of the coupled algorithm were compared with the engineering algorithm results, and the effectiveness and accuracy of the numerical simulation were validated. The numerical investigations shown that both the temperature field and stress field obtained by the coupled algorithm were slightly lower than which obtained by the engineering algorithm. These were considered to be impacted by the Bartz empirical formula and the one-dimensional isentropic flow assumption. Further experimental investigations shown that the exterior surface temperature and strain of the nozzle throat obtained by the coupled algorithm were much closer to the experimental results, which further verified the accuracy of the coupled algorithm....
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