Study on hybrid blue-IR laser welding on AZ31B magnesium alloy

Abstract

How to perform a laser welding is crucial to assure the quality of welds on magnesium alloys, and the challenges are the suppression of bubble generation and the reduction of pore defects. In this paper, hybrid blue-IR laser welding (HBI-LW) is proposed to improve the stability of a molten pool and keyhole; HBI-LW is produced by using dual coaxial lasers that have different wavelengths and spot diameters. A multi-physics heat flow model is developed to analyze the effect of composite heat sources on porosity quantitatively. The combined volumetric heat source model has been verified experimentally. The experiments show that when the laser power is 1800 W and the power of HBI is increased to 600 W, the porosity is formed at a lower level of about 0.5 %. The results are aligned well with that from numerical simulations on the proposed volumetric heat source model. In comparison with LW, HBI-LW is able to generate a larger melt pool and plasma plume and to smoothen the rear wall of a keyhole. This regulates the flow of the molten pool, suppresses the keyhole closure, and reduces the occurrence of keyhole collapse effectively. The dynamics of the keyhole and the forming mechanism of pores are investigated. This research provides theoretical and practical guides to suppress pore defects in laser welding on magnesium alloy.