Improvement of the Joint Performance in Laser Welding of Aluminium Alloys

Abstract

Considering the fuel consumption of cars, a light structure of aluminium alloys is desired for car bodies nowadays. However, fusion welding of aluminium alloys has some problems: reduction of joint efficiency, porosity formation, and hot cracking. In the present work, an investigation to improve the joint performance of laser welded joints has been carried out by the addition of Cu, Ni, and Zr to A6N01 alloy welds. An aluminium alloy plate of 2.0 mm in thickness with a filler metal bar was welded by a twin beam Nd: YAG laser facility (total power: 5 kW). The filler metals were prepared by changing the chemical compositions by adding elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 l/min was used. The defocusing distance was kept at 0 mm. At travel speeds of 3 to 9 m/min and at a laser power of 5 kW (front beam 2 kW, rear beam 3 kW), full penetration welds were obtained; whereas, at travel speeds of 12 to 18 m/min and the same power, partial penetration was observed. The joint efficiency of the laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining, and precipitation hardening. This type of hardening has been further considered by metallurgical examination.