Study On Friction Stir Welding Performance Of AZ31 Magnesium Alloy With Base Plate

Weld is one of the important processes to transform metal materials into engineering structures that can meet the needs of industrial fields.At present,the connection of magnesium alloy is mainly completed by traditional melting welding and riveting,and it is prone to problems such as porosity,thermal crack,large welding deformation and poor mechanical properties of joints.Friction stir welding is different from the traditional melting welding process.The heat input of welding is lower than the melting point of the base metal,and the welded metal plate does not melt.The metal is connected in the plastic state,which can avoid defects such as porosity and cracks.In this paper,friction stir welding of 1.5mm AZ31 magnesium alloy with base plate was carried out,to explore the influence of rotating speed,welding speed and pressure on the mechanical properties of welded joints,to determine the range of the best welding process parameters,and to study the macroscopic morphology,microstructure,vickers hardness and defects of the joints.In order to explore the optimal welding parameters of friction stir welding on AZ31 magnesium alloy and lay a foundation for further research on friction stir welding on 1.5mm AZ31 magnesium alloy with base plate.Friction stir welding was performed on 2mmAZ31 magnesium alloy firstly.The results show that when the rotating speed is 1000r/min,the welding speed is 30mm/min,and press amount is 0.15 ~ 0.20 mm,the welded joints have good surface and tensile efficiency up to 81.27%.The fracture mode of joint are fracture and stress direction about 45 ° fracture,and fracture location is the heat affected zone of the forward side.The hardness distribution of the cross section of the joint was unsymmetrical W shaped.The lowest point of hardness is the heat affected zone of the forward side,which corresponds to the fracture location.Experimental results of friction stir welding on 1.5mmAZ31 magnesium alloy with base plate are when the welding speed is 25mm/min with the welding speed which is within the range of 1000~1100r/min,the welding speed is 30mm/min and the welding speed which is within the range of 950 ~1050r/min,and the welding speed is 35mm/min and the welding speed is which within the range of 1050~1150r/min,the joints with high tensile properties can be obtained.When the welding speed is 25mm/min and the rotation speed is 1000r/min,the joint has the highest tensile strength(237.94Mpa),reaching 90.47% tensile efficiency of the base metal.The fracture form and hardness distribution are the same as 2mm AZ31 magnesium alloy friction stir welded joint.In this paper,the three-level and three-factor orthogonal experiment is established by taking the rotation speed,welding speed and down pressure as factors,and then the test results are analyzed and predicted by anova and neural network.In order to study the influence of welding process parameters on joint strength,we used variance analysis and artificial neural network to analyze the test data.The results show that the order of significant parameter on 1.5mm AZ31 magnesium alloy with base plate friction stir welding joint are welding speed > pressure amount > rotation speed.The strength prediction diagram obtained by the artificial neural network model is in good agreement with the actual test results.