Study On Fiber Laser Welding Of Aluminum Alloy With Filler Wire

Aluminum alloy is a desirable structure metal due to the low density, good navigability, long fatigue life and high strength, which is widely used in aerospace, shipbuilding, telecom cable, and so on. Because of the advantages of high welding efficiency, large depth-wide ratio, small grain size and narrow heat affected zone, laser welding has recieved an increasing attention to join aluminum alloys. However, the challenges for laser welding of aluminum alloys are the too many metallurgical defects, such as porosity, undercut cracks and so on, which reduces the joint mechanical properties. In order to improve the weld formation, reduce the metallurgical defects and enhance the joint quality, laser welding of aluminum alloys with filler wire is carried out in present study. The main results are listed as following.A newly developed laser, fiber laser is employed to study the laser welding of aluminum alloys including 2.5mm 5052, 2.2mm 7075 and 4mm 6061 aluminium alloys. The effects of process parameters such as laser power, welding speed, wire feed rate, defocusing distance, laser-wire distance, filler wire angle, shielding gas are studied in detail. Increasing laser power and decreasing welding speed increase the weld penetration depth due to the increasing heat input. According to the experiment results the optimal welding parameters are obtained. It is filler wire leading method, laser defocused distance -2mm, laser-wire distance 2mm, filler wire angle 60°and shielding gas flow rate 10L/min. In this study, at laser power 4kW the maximum welding speed of 2.5mm 5052 and 2.2mm 7075 aluminum alloys is 4.2 m/min and 4.5 m/min respectively, while at laser power 6kW, that of 4mm 6061 aluminum alloy reaches 3.6m/min.The experimental results show the joining strength of welded joints can be improved by reducing heat-input and is not sensitive to wire filling speed. For 7075 aluminum alloy, the joining strength of laser filling welded joint is higher than that of pure laser welded joints (259MPa). Besides, the joints with Al-Si wire can obtain the maximum joining strength, 350MPa compared to the joints with Al-Cu and Al-Mg filler wire. Because the Si element can improve the pool fluidity to reduce the metallurgical defects, then the joint with Al-Si wire gets the better joining strength.The formation mechanism of laser filling welded aluminum alloys are discussed and summarized by the observations, and the controlling methods are proposed in present study. The weld porosity is mainly caused by the instability of the laser keyhole. However, it can be reduced by increasing laser power, welding speed and wire filling speed.