A Study On Weld Seam Composition And Properties During Deep Penetration Laser Welding Of Aluminum Alloy

Against the mian problems existing in laser welding of aluminium alloys, in this paper, welding experiment of aluminum alloy5052is carried out by CO2laser and fiber laser. The penetration welding threshold of aluminum alloy5052is tested. It is mainly concerned about the influence of laser power, welding speeding, shielding gas flow rate and focusing distance on welding seam forming.Firstly, the the role of magnesium element in the aluminum alloys and the influence of its burming loss on the the mechanical properties of the weld joint are analysed in this paper. In deep penetration laser welding, laser beam with high power intensity focuses onto the work piece surface; the illuminated material is melt and vaporized. Due to the excitation and ionization of metal vapor, laser-induced plasma forms in the keyhole and above the work piece surface. In aluminum alloy5052, there are some alloying elements with low boiling point such as magnesium. Due to the fact that the boiling point of magnesium (1380K) is not only much lower than that of aluminum (2723K), but also only447K higher than the melting point of aluminum (933K), a part of magnesium element escapes from melt pool during laser welding. Magnesium element is a major strengthening element in aluminum alloys, the vaporization loss of magnesium results in reducing the mechanical properties of welding joint.Secondly, in order to study the buring loss of magnesium element in fiber laser welding of aluminum alloy5052, spectral analysis technology is used to monitor the keyhole plasma. A specially-designed device is first used to collect the spectral signals emitted from the keyhole plasma. Then, the influence of welding parameters on the Mg I spectral intensity is studied, and the Mg I spectral intensity in the radial and depth direction of keyhole is collected. In the experimental condition, the welding parameters have a big effect on the spectral intensity of magnesium element plasma. In the radial direction, the spectral intensity of Mg I decreases from the center to the edge of the keyhole; in the depth direction, from the top to the bottom of the keyhole, the spectral intensity of Mg I increases first and then decreases.Thirdly, magnesium element content test in the radial and depth direction of weld seam is conducted by an Electron Probe Micro Analyzer. Microhardness in the radial direction of weld zone is tested by402MVA Vickers hardness test machine. Tensile strength of the weld jiont is test by universal test machine. On the basis of these tests, the average Mg content, average microhardness in weld zone and the average tensile strength of weld joint at different laser power are obtained in this paper.Finally, the microstructures in the base material, heat affected zone and fusion zone are analyzed. Compared the above-observed Mg I spectral intensity with the above-detected Mg content, the mechanism of burning loss of magnesium element in laser welding of aluminum alloy5052is discussed. The relationship among the magnesium element loss rate, the microhardness loss rate and the tensile strength loss rate is established.