Abstract
By using the X-ray transmission imaging system, melt flows inside a molten pool were studied during laser welding of aluminum alloy at different welding speeds. Then, the correlation between temperature gradients along the direction of weld penetration and melt flows in the rear part of a molten pool was analyzed by using a three-dimensional numerical method. And the presented model was verified by experimental results. The corresponding investigation was carried out to further study the correlation between temperature gradient and melt flow behavior of the molten pool in the plate heated by preheating temperature. The results indicated that, in the rear part of the molten pool, the maximum flow velocity was located at the bottom of the molten pool. The melt metal in the rear molten pool caused by different welding speeds had significantly different flow trends. As the welding speed increased, the absorbed intensity on the keyhole front wall also increased as well as the recoil pressure that could maintain the keyhole opened. Consequently, the increase of the welding speed was more beneficial to improving the stability of the molten pool.
Highlights
Laser welding of aluminum alloys has been widely used in different industrial applications such as aerospace and vehicles because of its high productivity and low thermal input [1, 2]
The results indicated that, in the rear part of the molten pool, the maximum flow velocity was located at the bottom of the molten pool
By using the X-ray transmission imaging system and the numerical simulation, the correlation between temperature gradient along the direction of weld penetration and melt flow in the rear part of molten pool was studied during laser welding of aluminum alloy at different welding speeds and preheating temperatures
Summary
Laser welding of aluminum alloys has been widely used in different industrial applications such as aerospace and vehicles because of its high productivity and low thermal input [1, 2]. The complexity of the aluminum laser welding process induces a number of weld defects such as pore formation, undercutting, underfilling, and solidification cracking [3]. Some bubbles floated up and disappeared from the top surface and the amount of porosity was reduced, while others were captured at the solidifying front in the rear part of the molten pool, resulting in the formation of pores. Matsunawa [6] reported that the low viscosity of the aluminum melt promoted highly dynamical processes of molten pool. The authors found that the melt flow was from the top to the bottom around the keyhole and from the bottom near the keyhole tip to the rear-bottom surface near the solidifying front at the low welding speeds, which was different from those at the high welding speeds. Li et al [9] investigated the spatter formation and the molten pool behavior by using
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