Study On Pulse Laser Weaving Welding Of Al-Mg Alloy Sheet

In recent years,with the intensification of the energy crisis and the rapid development of the transportation industry,modern vehicles have become increasingly demanding on energy saving and emission reduction.The use of lightweight aluminum alloys to reduce the weight of car bodies has become a research hotspot in recent years.Al-Mg alloys have good weldability,low temperature toughness and excellent corrosion resistance through cold deformation and solid solution strengthening of Mg elements.However,due to the high reflectivity of Al-Mg alloy and the vigorous evaporation of Mg elements,the laser welding process is extremely unstable,and the molten pool fluctuates violently,resulting in pores,cracks,macro-morphological defects and poor mechanical properties.Aiming at these problems,this paper adopts pulse laser weaving welding technology and takes 0.8 mm thick 5052 aluminum alloy plate as the research object,and conducts specific research on the weld forming characteristics,microstructure and mechanical properties under pulse laser weaving welding.It provides a theoretical basis for the reliable laser welding of Al-Mg alloy.The main research contents are as follows:(1)Application of Nd: YAG pulsed solid-state laser to pulse laser of 5052 aluminum alloy with 0.8 mm thickness weaving welding experiment,discussed the influence of the change of weaving frequency on the macro surface morphology and cross-sectional morphology of the weld under a fixed weaving path and weaving width.Theoretical studies on the causes of welding defects and the mechanism of suppression of defects by weaving welding process.The results show that the pulse laser weaving welding process can significantly suppress welding defects such as undercut and spatter of welded joints.(2)Scanning electron microscope,electron backscatter diffraction module,and electron probe were used to detect the microstructure,texture orientation,and element distribution characteristics of laser weaving welded joints.It was found that the average grain size in the conventional weld was 39 μm and the texture strength was 6.24,while at a weaving frequency of 8 Hz,the average grain size in the weld was 19 μm and the texture strength was 4.54.In addition,it was found that as the laser weaving frequency increased,the proportion of equiaxed crystals in the weld increased,the proportion of small-angle grain boundaries increased,and the element distribution was more uniform.Finally,a quantitative analysis of the Mg element in the weld was carried out.The results showed that laser weaving welding did not aggravate the evaporation burning of the Mg element.(3)The longitudinal section of the welded joint under different weaving frequencies was obtained by mechanical grinding and polishing,and the distribution of pores in the longitudinal section of the weld seam was observed and counted using an optical microscope.The results show that the types of pores in the weld are mainly hydrogen pores.In addition,it was found that the laser weaving process has a significant effect on the suppression of pore defects in the weld,and when the swing frequency is 8 Hz,the target weld with no pores is obtained.(4)An Instron 5966 tensile testing machine was used to perform mechanical tensile experiments on the samples of laser weaving welded joints,and the fracture position and tensile fracture morphology of the samples were observed.The results show that the laser weaving welding process has an important effect on the tensile properties of the weld.With the increase of the weaving frequency,the tensile strength of the sample gradually increases,and finally the tensile strength is obtained at the weaving frequency of 8 Hz.About 85% of welded joints of base metal.The fracture positions of the samples are all at the center of the weld,and the fracture of the weld exhibits the characteristics of fine equiaxed dimples.