A novel strategy for metal transfer controlling in underwater wet welding using ultrasonic-assisted method

doi:10.1016/j.matlet.2020.127692

Materials Letters

Volume 270, 1 July 2020, 127692

https://doi.org/10.1016/j.matlet.2020.127692 Get rights and content

Highlights

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A novel lateral ultrasonic-assisted droplet transfer controlling method was developed.
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The proportion of unstable metal transfer mode was reduced by 23%
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The proportion of droplet repelled spatter was reduced from 9% to 4%.
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The weld appearance and microstructure refinement were enhanced.
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The content of coarse pro-eutectoid ferrite was decreased.

Abstract

In this work, a new lateral ultrasonic-assisted droplet transfer controlling method was innovatively developed in the underwater wet welding process. The ultrasonic acoustic streaming can overcome the resistance caused by arc bubble rising, promote the metal transfer and reduce the proportion of droplet repelled spatter from 9% to 5%. The proportion of unstable droplet transfer mode decreased from 64% to 41%, which obtain a welded joint that was smooth and free of defects. The proportion of pro-eutectoid ferrite was decreased while the weld metal presented a finer microstructure. As a feasible and high-efficiency method, it is expected to spread the application of underwater wet welding in ocean and coastal engineering.

Graphical abstract

Introduction

As a low-cost and easily operable welding technology, underwater wet welding has been widely used in the construction and repair of offshore steel structures such as nuclear power plants and offshore oil platforms [1], [2]. Flux-cored arc welding (FCAW) has a great potential for using in deep-water environment because it can be automated more easily than traditional manual metal arc welding [3]. However, because the wet welding process is conducted directly in water, the burning arc is constantly heating water and generating vapor bubbles. The frequent rising and collapsing of arc bubbles have significant effects on the arc stability and metal transfer process [4]. Depend on high-speed imaging technique, four fundamental metal transfer modes are found [5], [6]. Among of these, the “globular repelled transfer mode” caused by gas flow drag force is the most unstable metal transfer mode. Under certain conditions, the swinging droplet in this mode cannot enter into the weld pool and cause spatter loss [1]. Therefore, it is important to control the droplet transfer and improve the process stability. At present, many methods such as pulsed wire feeding [7], pulse current welding [8], magnetic field [9] CMT welding [10] and laser-MAG hybrid welding [11] have been employed to enhance the stability of droplet transfer. But not all methods are applicable for the wet welding in the special underwater environment and the effects of them are far from satisfactory. Besides, the using of dedicated and complex device will inevitably increase the total cost. Therefore, a low-cost method with operability, universality and high-efficiency should be developed to control droplet transfer and spread the application of wet welding.

In this paper, we proposed a novel lateral ultrasonic-assisted droplet transfer controlling (LUADTC) method. The feasibility of LUADTC to promote the droplet transfer process during underwater wet FCAW were discussed.

Section snippets

Experimental

H40 marine steel and a rutile type flux-cored wire with a diameter of 1.6 mm were selected. Constant voltage power source was employed and the welding with current polarity of DCEP was carried out in a transparent acrylic water tank. The specific parameters are as follow: welding voltage 29 V, wire feeding speed 3 m/min, welding speed 2 mm/s, wire extension 15 mm, water depth 0.5 m.

A set of ultrasonic-assisted device was installed at the one side of welding torch, as shown in Fig. 1(a). It

Results and discussions

During underwater wet welding, the water surrounding arc was heated to a boil that it became vapor bubble called “arc bubble”. As these bubbles rise up, the gas flow drag force would become a repulsive force and repelled the droplet transfer. Fig. 2(a) shows a typical droplet transfer process in the conventional wet welding method (see details in Supplementary Movie 1). Obviously, the rise up of arc bubble caused a notable impact on the droplet. The strong repulsive force resulted in that

Conclusions

In summary, the novel LUADTC method was successfully developed to control and promote the metal transfer during underwater wet welding process. Compared with conventional wet welding, the proportions of unstable transfer mode and droplet repelled spatter were reduced by 23% and 4%, respectively. The smoother welded joint with fewer defects could be obtained. The average toughness of joints was increased by 20% due to the microstructure refinement of weld metal.

CRediT authorship contribution statement

Hao Chen: Conceptualization, Data curation, Methodology, Investigation, Writing - original draft. Ning Guo: Supervision, Funding acquisition, Writing - review & editing. Zhihao Zhang: Resources, Investigation. Cheng Liu: Data curation, Methodology. Li Zhou: Investigation, Validation. Guodong Wang: Project administration, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors are grateful for the financial support from the Fundamental Research Funds for the Central Universities (Grant Nos. HIT.NSRIF.201602, HIT.NSRIF.201704, HIT.MKSTISP.201617), the Key Technology Research and Development Program of Shandong (Grant Nos. 2017CXGC0922, 2018GGX103003) and Natural Science Foundation of Shandong Province (Grant Nos. ZR2017QEE005, ZR2017PEE010).

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