Effect of plate thickness on weld pool dynamics and keyhole-induced porosity formation in laser welding of Al alloy
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ORIGINAL ARTICLE
Effect of plate thickness on weld pool dynamics and keyhole-induced porosity formation in laser welding of Al alloy Peng Liu 1 & Lijin Huang 1,2 & Lu Gan 1 & Yuyu Lei 1 Received: 13 May 2020 / Accepted: 21 July 2020 / Published online: 3 October 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract A three-dimensional (3D) transient numerical model is developed to simulate the keyhole dynamics, melt flow, and keyhole-induced porosity formation. The influence of the plate thickness on keyhole-induced porosity size and number is thoroughly investigated. The simulation results show that the average keyhole depth in plate thickness of 3, 6, and 10 mm is 2.07 mm, 1.89 mm, and 1.77 mm, respectively, and the value of keyhole depth reaching the quasi-steady state is 34 ms, 28 ms, and 14 ms, respectively. Compared to the thinner thickness plate, it is not easy to see the phenomenon of bubble amalgamation in the thickness of 10 mm under the parameter of low laser power and high welding speed. The less porosity in thicker plate laser welding is attributed to lower frequency of keyhole collapse, higher ratio of keyhole open after keyhole collapse to total keyhole collapse number, lower ratio of bubble number to total keyhole collapse number, higher ratio of bubble escape to the total bubbles number, and lower ratio of bubble amalgamation to the total. Keywords Plate thickness . Porosity . Laser welding . Al alloy
1 Introduction Aluminum (Al) is the most abundant metal element on the planet in the earth, which has become one of the most commonly used alternative materials in steel design and manufacturing [1]. Meanwhile, owing to the high specific strength, outstanding corrosion resistance, and superior machinability, Al alloys possess extensive applications in aerospace industry, naval vessels, and high-speed trains [2]. Recently, it is certified that connections of Al alloys can be joined by tungsten inert gas welding (TIG), melt inert-gas welding (MIG), and submerged arc welding (SAW), among others [3]. Comparison with traditional
* Lijin Huang [email protected] 1
Shipbuilding Technology Research Institute, Shanghai 200032, China
2
Shanghai Key Laboratory of Material Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, China
fusion welding processes and laser welding gets the advantages of fast speed, high penetration capability, low heat input, and low distortion [4, 5]. Due to the smaller surface tension, viscosity, and greater evaporation rate of Al alloy, keyhole-induced porosity defect is the main problem in fiber laser welding, which obviously weakens the joint strength [6]. The keyholeinduced porosity is formed from the bubble caused by the unstable keyhole [7]. Many scholars had taken experimental methods to study [8, 9]. Berger [10] discovered that bubbles are generated at the rear and tip of the keyhole. His research is limited in welding process of nonmetals owing to different physical material properties. Kawahito [11] thought that the
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