Effect of Droplet Impingement on the Weld Profile and Grain Morphology in the Welding of Aluminum Alloys

Abstract

To achieve a better understanding of the effect of droplet impingement on the weld profile and grain morphology, welding with vertical and inclined torches in the double pulsed-gas metal arc welding of aluminum alloy were compared. When using vertical welding, the grains along the wall of the finger-like penetration (FLP) were refined by a more violent flow driven by droplet impingement running in the confined space created by FLP. When using inclined welding, the sharp inflection point disappeared and the curved columnar grains emerged on the non-impact action side, which was attributed to the gradually weakened impingement at that location. Moreover, when the penetration became shallower due to a low mean current, the droplets impinged alternately along split trajectories, causing significant changes in the grain morphology, such as creating grains which were sharply shortened by the direct impact of droplet impingement at impact point. The change of trajectory was ascribed to the variation of the width/depth ratio of FLP, which changed the magnitude of the contradiction between the room required by the fluid flow driven by droplet impingement and the space supplied for that by FLP.

Mechanism of the Influence of Weld Pool Wall Constraint on Weld Profile Formation in Gas Metal Arc Welding of Aluminum Alloy

“…Figure 5 shows the height, width, and forming coefficient of the weld reinforcement It can be seen from the above analysis that the shape of the upper surface of the molten pool is jointly determined by the droplet impact, which plays an active driving role, and the wall constraint, which plays a passive restraining role. When the base metal surface is not completely penetrated, the droplet impact promotes the molten metal to flow in the molten pool [24]. When it flows to the bottom wall of the molten pool, the solid bottom wall restricts a large amount of molten metal to flow backward, thus, forming an upper surface reinforcement in the central plane.…”

Special Issue on “Mechanical Behaviour of Aluminium Alloys”

“…Despite the progress made over the last few decades, many problems remain unsolved. For example, Zhang et al [10] compared the effect of welding direction, namely vertical and inclined configurations, on the weld profile and grain morphology obtained using double pulsed-gas metal arc welding processes.…”

Profile Map of Weld Beads and Its Formation Mechanism in Gas Metal Arc Welding

“…Moreover, the profile of a weld bead is also impacted by the direction of droplet impingement. Zhang et al [11] reported that the center lines of the lower part and the upper portion no longer coincides once the welding torch is inclined. Although the molten behavior has been studied quite adequately by the mentioned researches, all the weld pool walls involved above are almost in their solid state, and the role played by the wall in affecting the flow pattern and the resultant bead profile is rarely reported.…”