Mitigation of porosity in adjustable-ring-mode laser welding of medium-thick aluminum alloy

Adjustable-ring-mode laser welding (ARM-LW) offers a novel approach to minimize porosity in medium-thickness aluminum alloy joints. However, the suppression mechanism and optimization strategy of reducing porosity for ring-mode laser remain unclear. A combination of experiment and simulation was utilized to narrow the gap. The findings demonstrated that ring-mode laser effectively slows the increase of porosity with rising penetration depth compared to traditional Gaussian laser welding. The pore formation involves bubble generation induced by keyhole instability and bubbles being captured by the solidification front. As ring power share increases, the keyhole opening widens and becomes more stable, which enhances the energy absorption of keyhole walls, particularly in the bottom and middle sections. This enhances the keyhole stability and reduces bubble formation resulting from keyhole collapse. Additionally, as ring power share grows, a decrease of 63.2 % of -X-velocity suggests that bubbles are moving at a slower pace away from the keyhole bottom, increasing the chances of them being captured by keyhole and eventually vanishing; however, a decrease of 52.4 % of +Z-velocity raises the possibility of bubbles being trapped by solidification front if not caught by keyhole. Finally, a comprehensive discussion and analysis of how to mitigate porosity during ARM-LW are presented. A criterion—minimizing penetration to spot diameter ratio (PDR)—was proposed to guide ring power share selection. The insights into keyhole fluctuation and bubble evolution mechanisms outlined here can guide mitigating porosity in laser welding of medium-thickness aluminum alloy plates.