Search

In this work, magnetic field-assisted autogenous gas tungsten arc welding (GTAW) of low carbon steel has been studied. The external magnetic field was generated by custom made rectangular shaped samarium cobalt permanent magnets which were arranged in a manner to generate a cusp-type magnetic field (CMF). The impact of CMF on the morphology and microstructural evaluation of the weld joints were examined prudently using optical microscope, Field-emission scanning electron microscope and X-Ray Diffraction technique. The experimental results exhibited that the CMF assisted GTAW produce joints with better mechanical and metallurgical properties compared to conventional GTAW. In CMF assisted welds, width of weld beads was reduced by an average of 4% and depth of penetration was increased by 13%. Temperature measurement on the work piece showed a significant amount of temperature decrease for the same amount of heat input under the influence of the CMF. An improvement in grain refinement was observed in the heat-affected zone (HAZ) adjacent to fusion boundary by 12% and HAZ adjacent to base metal by 15% compared to conventional GTAW, which in turn promoted a considerable increase in hardness. The tensile properties in CMF assisted welds were enhanced by 3% and 8%, respectively, for an increase of heat inputs from 0.34 to 0.45 kJ mm−1. [ABSTRACT FROM AUTHOR]

Fiber laser beam welding experiments are carried out on 2 mm thick plates of Ti-6Al-4V alloy at various welding conditions. A specially designed workpiece fixture with shielding gas delivery system is fabricated and effectiveness of shielding gas is confirmed by energy dispersive X-ray spectroscopy analysis. Two different types of bead cross-sections i.e. T-shaped and nearly X-shaped beads are observed at different line energies. After experiments, width and area of fusion zone and size of heat affected zone are measured and further analyzed. The microstructural studies at different locations in heat affected zone and also in fusion zone are carried out with optical microscope and their morphologies are compared at different welding conditions using field emission scanning electron microscope. The porosities are observed in both T and X-shaped weld beads at different line energies. However, their sizes are in acceptable range as per BS EN:4678 standard. The maximum microhardness is found in fusion zone due to the presence of large amount of α′ martensite. The line energy utilization factor is higher for T-shaped bead than X-shaped bead. The tensile strength of T-shaped bead is lower than X-shaped bead due to higher non-uniformity in the distribution of plastic strain. The experimental results show that T-shaped welding conditions are favorable while considering full penetration in keyhole mode, narrower weld width and lesser heat affected zone. [ABSTRACT FROM AUTHOR]

In the present study, experimental investigations of fiber-laser-beam-welding of 5 mm thick Ti-6Al-4V alloy are carried out based on statistical design of experiments. The relationship between the process parameters such as welding power, welding speed, and defocused position of the laser beam with the output responses such as width of the fusion zone, size of the heat affected zone, and fusion zone area are established in terms of regression models. Also, the most significant process parameters and their optimum ranges are identified and their percentage contributions on output responses are calculated. It is observed that welding power and speed plays the major role for full penetration welding. Also, welding power shows direct effect whereas welding speed shows the inverse effect on the output responses. The bead geometry is influenced by the defocused position of the laser beam due to the change in power density on the workpiece surface. However, overall fusion zone area is unaffected. Mechanical characterization of the welded samples such as microstructural analysis, hardness, and tensile tests are conducted. It is noticed that the hardness value of the FZ is higher than the HAZ and BM zone due to the difference in cooling rate during welding which promotes the formation of α′ martensitic phase in the FZ. Also, an average hardness value in the FZ is compared for two different defocusing positions (i.e. 1 and 2 mm). It is found that hardness value is higher for 1 mm defocused position than 2 mm due the decrement in grain size below a critical range at 2 mm defocused position. The ultimate tensile strength and % elongation of the welded samples are degraded as compared to BM which can be further improved by post heat treatment. [ABSTRACT FROM AUTHOR]