CO₂ laser weldability of aluminium alloys (Report 1): Effect of welding conditions on melting characteristics

Summary

A series of systematic studies was undertaken to clarify the effect of CO₂ laser welding conditions on melting characteristics, porosity formation, cracking susceptibility, hardness profiles, macro- and micro-distribution of Mg, and tensile properties of aluminium alloys. Bead-on-plate welding was performed on different commercially available alloys such as A5052, 5083, 5182, 6061 and 7N01 with a CO₂ laser under various conditions of laser power, welding speed and defocused distance. In this paper, the influence of various welding conditions on melting characteristics was investigated from a fundamental viewpoint. In particular, laser beam modes and pressure distribution under various gas flow rates were measured, and it was consequently demonstrated that melting behaviour was greatly affected by the laser mode in the welding direction and the gas flow rate or pressure. Also the effect of Ar/He gas ratio on melting was investigated, and it was revealed that the use of Ar was beneficial to weld more highly-conductive and reflective alloys at lower power and higher welding speed, while a higher content of He was good for higher power and lower welding speed. Furthermore, it was confirmed that a larger amount of Mg was evaporated even under conditions producing a shallow weld molten pool leading to more deeply penetrated welds.