Weld pool fluid flow can affect the penetration of the resultant weld significantly. In this work, the computer simulation of weld pool fluid flow and its effect on weld penetration was carried out. Steady-state, 2-dimensional heat and fluid flow in stationary arc welds were computed, with three driving forces for fluid flow being considered: the buoyancy force, the electromagnetic force, and the surface tension gradient at the weld pool surface. The computer model developed agreed well with available analytical solutions and was consistent with weld convection phenomena experimentally observed by previous investigators and the authors. The relative importance of the influence of the three driving forces on fluid flow and weld penetration was evaluated, and the role of surface active agents was discussed. The effects of the thermal expansion coefficient of the liquid metal, the current density distribution in the workpiece, and the surface tension temperature coefficient of the liquid metal on weld pool fluid flow were demonstrated. Meanwhile, a new approach to free boundary problems involving simultaneous heat and fluid flow was developed, and the effort of computation was reduced significantly.

Fluid flow and weld penetration in stationary arc welds

Wire arc additive manufacturing (WAAM) offers a potential approach to fabricate large-scale magnesium alloy components with low cost and high efficiency, although this topic is yet to be reported in literature. In this study, WAAM is preliminarily applied to fabricate AZ31 magnesium. Fully dense AZ31 magnesium alloy components are successfully obtained. Meanwhile, to refine grains and obtain good mechanical properties, the effects of pulse frequency (1, 2, 5, 10, 100, and 500 Hz) on the macrostructure, microstructure and tensile properties are investigated. The results indicate that pulse frequency can result in the change of weld pool oscillations and cooling rate. This further leads to the change of the grain size, grain shape, as well as the tensile properties. Meanwhile, due to the resonance of the weld pool at 5 Hz and 10 Hz, the samples have poor geometry accuracy but contain finer equiaxed grains (21 μm) and exhibit higher ultimate tensile strength (260 MPa) and yield strength (102 MPa), which are similar to those of the forged AZ31 alloy. Moreover, the elongation of all samples is above 23%.

Wire Arc Additive Manufacturing of AZ31 Magnesium Alloy: Grain Refinement by Adjusting Pulse Frequency

Effects of high-intensity ultrasonic-wave emission on the weldability of aluminum alloy 7075-T6

Shaped metal deposition method using gas tungsten arc welding is a novel manufacturing technology that can be used for fabricating solid dense parts in layered manufacturing. This paper reports for the first time using the pulsed current shaped metal deposition technique for fabricating components using cold wire of AISI 308LSi stainless steel. The aim of this work was to investigate and compare the effect of pulse frequency and other deposition process parameters on the morphology aspects and microstructure characteristics of the manufactured components using pulsed and continuous current processes. The obtained results reveal that the structure of the deposited specimens produced via pulsed arc current is generally having finer grains, high residual ferrite, and absence of columnar grains. Pulse frequency and current ratio have a significant influence on the surface morphology and microstructure of the manufactured parts. Good metallurgical bonding with no sensitization effects can be seen in all tested specimens. The presented additive layered manufacturing method can be recommended for near net-shaped processing of austenitic stainless steel components, and it can be used as an alternative manufacturing method for fabricating metal components with free defects, higher corrosion resistance, and superior mechanical properties.

Microstructure characterization of SS308LSi components manufactured by GTAW-based additive manufacturing: shaped metal deposition using pulsed current arc

The effect of arc oscillation on grain structure and solidification cracking in GTA welds of 5052 aluminum alloy was investigated using a four-pole magnetic arc oscillator and a modified fish-bone crack test. Two different mechanisms of crack reduction were identified: one in the low frequency range of arc oscillation and the other in the high frequency range. The former was the alteration of the orientation of columnar grains, while the latter was grain refining. Neither mechanism was operative in the intermediate frequency range and solidification cracking was severe, especially when the amplitude of arc oscillation was small. Alteration of grain orientation was obtained in welds made with transverse and circular arc oscillations, but not longitudinal arc oscillation. Grain refining, on the other hand, was achieved in welds made with all three types of arc oscillation patterns. The differences between the response of alloy 5052 to arc oscillation and that of alloy 2014 observed previously were discussed.

Grain structure and solidification cracking in oscillated arc welds of 5052 aluminum alloy

The effect of the electromagnetic vibration of the arc and the influence of current pulses on the microstructure of welded tantalum sheets were investigated. Optimum conditions of arc vibration and of current pulses for refined microstructure in the fusion zone and in the heat-affected zone (HAZ) were determined. At these conditions equiaxed grains in the fusion zone and a decreased grain size in the HAZ were obtained. The effect of the welding rate on the microstructure was also investigated. Mechanical properties of the welds with improved microstructure obtained by the above techniques were compared with the properties of welds obtained by conventional TIG techniques and with those of the parent metal. Slight improvement in yield stress and tensile stress and significant improvement in elongation were observed in the improved welds, compared to welds obtained by conventional techniques.

Effect of arc vibration and current pulses on microstructure and mechanical properties of TIG tantalum welds

A two-dimensional mathematical model was developed to calculate the temperature distribution during welding of thin tantalum sheets. The solution of the unsteady heat flow equation was obtained employing a computer program based on the finite difference method. The model does not require any assumptions regarding the shape of the welding pool. Arc parameters, radiative and convective heat losses and the dependence of the relevant physical properties on temperature are taken into account. The shape of the welding pool and isotherms are calculated and compared to experimental results.

Computation of temperatures in thin tantalum sheet welding

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Effect of arc vibration and current pulses on microstructure and mechanical properties of TIG tantalum welds

Computation of temperatures in thin tantalum sheet welding