Fibre laser welding of high-alloyed Al-Zn-Mg-Cu alloys

The theoretical fundamentals of laser weldability of metals are surveyed and relevant thermophysical parameters are identified such as vapour pressure, keyhole pressure, beam irradiance, surface tension and viscosity. The derived approach for improving the laser weldability implies the use of a Yb fibre laser with an initial large beam diameter, a top-hat beam profile and a high laser power, which enables the formation of a large and stable keyhole during deep penetration welding. For validating the effectiveness of the developed approach, it is applied to various high-alloyed and hard-to-weld Al-Zn-Mg-Cu alloys. Defect-free welds are obtained even for AA7034 - the alloy with the highest (Zn+ Mg+ Cu) content commercially available. As reference, the same alloys are welded by using a conventional Nd:YAG laser with a small beam diameter, a Gaussian beam profile and medium laser power. The laser weldability deteriorates with increasing (Zn+ Mg+ Cu) content in terms of porosity and excess of penetration. The obtained results highlight the importance of the laser system used on the laser weldability of Al-Zn-Mg-Cu alloys. (C) 2016 Elsevier B.V. All rights reserved.