Combined effect of flux and welding parameters on chemical composition and mechanical properties of submerged arc weld metal

Prediction of microstructure and mechanical properties of multipass SAW

Grain refinement is an important opportunity to improve mechanical properties of fusion welds and the weldability (susceptibility to solidification cracking) of the base metal. In this study, grain refinement was achieved in aluminium welds through additions of grain refiner to the weld metal. Increasing grain refiner additions led to a decrease of the weld metal mean grain size (down to −86 %). The grain refinement efficiency was the highest in commercial pure Al (Alloy 1050A, Al 99.5), followed by Alloy 6082 (Al Si1MgMn) and Alloy 5083 (Al Mg4.5Mn0.7). To investigate this clear influence of alloy content on grain size, the undercooling parameters P and Q were calculated. Temperature measurements revealed that solidification parameters such as solidification growth rate or cooling rate vary significantly along the solidification front, dependent upon torch speed and alloy. On the basis of this comparison, an analytical approach was used to model the columnar to equiaxed transition (CET). Moreover, wavelength dispersive X-ray spectroscopy (WDS) and transmission electron microscopy (TEM) analyses revealed particles rich in Ti and B that are probably TiB2 particles coated by Al3Ti nucleating Al grains during solidification. Also, Ti/B contents needed in commercial filler wires to allow optimum weld metal grain refinement were calculated dependent upon base alloy and welding process.

Understanding grain refinement in aluminium welding

Effect of controlled atmosphere on the mig-mag arc weldment properties

The hybrid additive manufacturing which involves direct metal deposition and high-speed milling has been considered as an effective process to make high performance products with well surface finish. Research that have been reported indicate that continuous energy sources can lead to intolerable residual stress and distortion even after the parts are processed by machine tools. Therefore, a hybrid additive manufacturing machine tool based on pulse laser wire depositing is established taking advantage of its intensive exposure. The designed work area of the hybrid AM machine tool is 50 mm × 50 mm × 100 mm. On this basis, a set of preliminary experiments are carried out to study the performance of the proposed hybrid AM process. Both the substrate and the wire are stainless steel (SUS304), and the wire diameter is 0.6 mm. Depositing trails were kept by oxide film since shield gas is not used during the deposition. Results show that stabilization of the process has a strong impact on both the surface finish and the microstructure. Moreover, experiment results indicate that wire feeding performance is the critical factor influencing the product performance due to the small weld pool size and the rapid melting and solidifying. Typical macrodefects of the fused welding and the exclusive flaw of additive manufacturing are detected. Microstructures show that column grains less than 1 μm dominate the deposition zone, where the column grains grew in the direction of depositing on the middle layers and along the curvature direction on the top surface. A thin wall about 0.5 mm wide is milled, and the result shows that the surface of the bead is greatly improved and no defects are detected after the thin wall is cut. However, the trapezoid cross section indicates that a further study on cutting is still demanded.

Study of hybrid additive manufacturing based on pulse laser wire depositing and milling

The purpose of this work is to investigate the relative influence of electrochemical and thermochemical reactions on the weld metal chemistry in a direct current submerged arc welding process. Chemical analyses were carried out on the melted electrode tips, the detached droplets and the weld metal for both electrode-positive (reverse) polarity where the welding wire is anodic and electrode-negative (straight) polarity where the welding wire is cathodic

Effect of electrochemical reactions on submerged arc weld metal compositions

Aluminum alloy welds are often plagued by their susceptibility to hot tearing. The addition of titanium or zirconium is known to reduce the susceptibility through grain refinement. Previous models have suggested that these elements need merely to be contained as an alloy addition without concern for the form of the addition in the consumable prior to welding. The form of the titanium or zirconium addition was found to have a bearing on the effectiveness of the grain refinement addit ion. Results from this research revealed the intermetallic phase of the addit ion (TiAI3 or ZrAI3) must be present prior to welding to achieve the desired grain refinement. The solidification kinetics were also found to have a significant effect on the grain refinement achieved with the intermetallic additions.

Influence of solidification kinetics on aluminum weld grain refinement

The electrochemical transfer of oxygen was investigated for electrode negative and electrode positive polarities in the submerged arc, shielded metal arc and gas tungsten arc welding processes. Analysis of the welds showed that electrochemical reactions as well as thermochemical reactions are significant in altering the oxygen content of the weld metal. The oxygen transfer in the submerged and shielded metal arc welding processes is strongly influenced by electrochemical reactions at the slag/metal interface, and oxygen transfer in gas tungsten arc welding is strongly influenced by electrochemical reactions at the plasma/metal interface. The electrochemical oxygen reactions at the slag/metal interface include oxygen pickup at the anode and oxygen refining at the cathode. Electrochemical oxygen reactions at the plasma/metal interface include the refining of oxygen at the anode and pickup at the cathode. Electrochemical reactions have the greatest influence on weld metal chemistry at high welding currents and at slow weld travel speeds.

Electrochemical oxygen transfer during direct current arc welding

By substituting zirconium-boron additions for titanium-boron additions in the weld deposit, further understanding of the role of specific microalloying additions on the suppression of grain boundary ferrite and the promotion of the intragranular formation of acicular ferrite in low carbon steel weld metal is achieved.

R. H. Frost

Papers

Effect of electrochemical reactions on submerged arc weld metal compositions

Influence of solidification kinetics on aluminum weld grain refinement

Electrochemical oxygen transfer during direct current arc welding

The Influence of Zirconium and Boron on Low Carbon Steel Weld Metal Microstructure