Microcracking and Mechanical Properties in Laser-Arc Hybrid Welding of Wrought Al-6Cu Aluminum Alloy
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Automated laser welding can precisely control the welding solidification process by accurately setting the heat input and welding speed. Precise control can improve weld quality. However, laser welding of aluminum (Al) alloys has a drawback in the instability of the laser-beam-induced keyhole, which easily produces pores.[1,2] Laser-arc hybrid welding (LAHW) inherited the advantages of laser welding, but its strong heat source interaction effect overcomes the drawbacks of laser welding.[3] Because of this advantage, LAHW has been successfully used to weld Al-Mg alloys,[4,5] Al-Mg-Si alloys,[6,7] Al-Zn-Mg-Cu alloys,[8] and Al-Li alloys.[9] To eliminate the pores and improve the welding efficiency, welding speeds generally faster than 1.5 m/min and larger arc heat input are used in LAHW of Al alloys.[10] The faster welding speed leads to a rapid solidification rate of the molten pool according to the mechanism of solidification cracking. It forms the crack
CHEN ZHANG is with the Institute of Technological Sciences, Wuhan University, Wuhan 430072, China. HU ZHANG, LEI WANG, MING GAO, and XIAOYAN ZENG are with the Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China. Contact e-mail: [email protected] Manuscript submitted November 4, 2017. Article published online July 20, 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A
because the occurring intergranular gap is more difficult to fill.[11] The cracking problem has been solved in the LAHW with Al-Mg alloys and Al-Mg-Si alloys.[7] However, due to a wider solidification temperature range, the ease of solidification shrinkage, and the ease of forming a eutectic, the intergranular gap of Al-Cu alloys is more difficult to fill, and the cracking sensitivity is higher.[11] This was proven by the arc welding and casting process of Al-Cu alloys.[12] This research conducted the LAHW of Al-Cu alloys, which can eliminate the macrocracks. However, subtle microcracks existed in the tensile fractures of some samples, which reduced their tensile properties. The two key parameters of welding speed and heat input were introduced into a more advanced prediction model for the solidification crack sensitivity, which was in good agreement with the experimental results. The cracking mechanism was explained, and the crack-free welds were made under the optimized welding processes. An IPG 6-kW fiber laser and a Fronius arc welder were employed to produce butt welds of two 250 mm 9 150 mm 9 6 mm Al-6Cu (AA2219) alloy plates. Because the previous research showed that the joint welded by the ER5087 (Al-Mg) wire filler had higher strength than the Al-Cu wire,[13] the ER5087 wire with a diameter of 1.6 mm was used. The welding parameters are shown in Table I. The shielding gas was 99.99 pct argon with a flow rate of 20 L/min. The laser beam was focused by a lens having a focal length of 250 mm to obtain a focus spot with the diameter of 0.3 mm. The defocusing distance of the laser beam was 3 mm. The incident laser beam was 10 deg to the vertical and
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