In the high-stakes world of construction and manufacturing, particularly in the energy sector, the quest for stronger, more efficient welding techniques is unending. A recent study led by A. Baghbani Barenji from WMG, The University of Warwick, has shed new light on the intricate dance of cooling rates, intermetallic compounds, and zinc vapours in laser welding. The findings, published in the Journal of Advanced Joining Processes, could revolutionize how we join dissimilar metals, especially in critical energy infrastructure.
Baghbani Barenji and his team delved into the complexities of welding hot-dip galvanised steel to aluminium sheets using a continuous wave (CW) laser. Their focus was on understanding how different cooling methods—passive and active—affect the formation of intermetallic compounds (IMCs) and the behaviour of zinc vapours, both of which are pivotal for joint strength. “IMCs are the most decisive factor in welding steel to aluminium,” Baghbani Barenji emphasized, highlighting the critical role these compounds play in the welding process.
The study revealed that active cooling, which involves using a cooling agent like water, significantly alters the welding dynamics. Without beam oscillation, the cooling rate increased by 34% when switching from passive to active cooling. However, with beam oscillation—a technique that moves the laser beam laterally to enlarge the weld area—the increase was a mere 2.5%. This discrepancy underscores the complex interplay between cooling rates, beam oscillation, and the resulting metallurgical properties.
One of the most striking findings was the impact of cooling rates on IMCs and zinc vapours. Faster cooling reduced the total amount of IMCs and the Fe2Al5 phase, which is known to be brittle and detrimental to joint strength. This led to an increase in joint strength. However, the hastened cooling also exacerbated spattering and weld discontinuity due to insufficient time for zinc vapours to outgas from the molten pool. This effect was more pronounced with beam oscillation, which creates a larger molten pool.
The commercial implications of these findings are vast, particularly for the energy sector. The ability to control cooling rates and beam oscillation could lead to more robust welds in critical infrastructure, such as offshore wind turbines and nuclear power plants, where dissimilar metals are often joined. “Active cooling with water flow at 10 °C achieved 60% joint efficiency compared to parent aluminium,” Baghbani Barenji noted, highlighting the potential for significant improvements in welding efficiency and strength.
Moreover, the study showed that while beam oscillation enlarges the connection area, the average shear stress was relatively lower compared to the case without oscillation. This was attributed to the increased thickness of the IMCs. Active cooling with beam oscillation reduced joint efficiency to 54%, but with half the strength variation, indicating a trade-off between joint strength and consistency.
The research published in the Journal of Advanced Joining Processes, also known as the Journal of Advanced Welding Processes, underscores the need for a nuanced understanding of welding parameters. As the energy sector continues to evolve, with a growing emphasis on renewable energy and sustainable materials, the insights from this study could pave the way for more efficient and reliable welding techniques. The future of welding in the energy sector may very well lie in the delicate balance between cooling rates, beam oscillation, and the behaviour of intermetallic compounds and zinc vapours.