Study On Fiber Laser Welding Process Of AZ31B Magnesium Alloy

Magnesium alloy as the 21st century green engineering metal structure material with high specific strength high specific stiffness dimension stability damping shock absorption performance is good,and good machinability,and unique advantages such as easy to recycle in the field of aerospace vehicles,such as medical devices and energy has wide application background.Magnesium alloy has the flammability melting point and low thermal conductivity and electrical conductivity characteristics of large chemical properties and lively,lead to welding process will encounter many difficulties,but the welding is a key technology to further promote the applications of magnesium alloys.At present,there are many welding methods for magnesium alloys.Due to the characteristics of high deformation and high power density of the small welding speed of optical fiber laser welding,more and more researchers are concerned.So this paper adopts the YLS 10000optical excitation device of 5 mm thick AZ31B magnesium alloy welding,different welding parameters on weld forming the influence law of microstructure and mechanical properties,in actual production application for magnesium alloys provide effective theoretical basis and reference value.The experimental results show that the laser power and welding speed of AZ31B magnesium alloy are two important parameters affecting the macro morphology and microstructure of the weld.When the laser power increases or the welding speed decreases,the welding heat input will increase,and the weld depth of the weld will increase.Microstructure of weld area to make use of metallographic microscope observation,found that the weld zone are fine equiaxed grain structure,but the microstructure of weld area grain size increases with the increase of welding heat input.The initial phase alpha-Mg was found only in the grain boundary and in the grain.At the laser power of 3000W,the welding speed is 3000mmmin^-1,blowing side protective gas 20L/min,back blowing as the protective gas 10L/min,defocus amount is 0,the microhardness of the fusion zone of the welded joint is 56.9HV lower than the parent material hardness of 59HV.the average tensile strength was 235MPa,reached 92.2%of that of the base material,the fracture occurred in the fusion zone,the characteristics of the fracture morphology of brittle fracture.During the experiment,it is found that there is a hole in the weld,mainly due to the excessive cooling of the molten pool during the welding process,and the hydrogen bubbles can not overflow;The inclusion of oxide MgO exists in the welded joint;The mechanical properties of welded joints are affected by other welding defects such as unsolder and collapse.But by the welding process parameters optimization of the welding environment protection and select high-quality raw materials and cleaning before welding,can effectively reduce the defects in laser welding of magnesium alloy,access to quality of welding joint.