Microstructure And Properties Of Activating-Double Arc Welding Of Magnesium Alloy

In this paper,the effect of bypass current,welding voltage and welding speed on the weld performance was studied by using the DE-GMAW(Double Electrode Gas Metal Welding)of 2mm thick AZ31 B magnesium alloy,a relatively suitable welding parameter is obtained.On the basis of this welding parameter,the effect of SiC coating on the weldability of AZ31 B magnesium alloy was studied by coating a layer of activating flux SiC on the surface of the base metal.In this experiment,the influence of each parameter on the weld forming was studied by analyzing the shape and weld size of the weld.The influence of the parameters on the performance of the joint was studied by analyzing the microstructure,microhardness and tensile strength of the joint.The results show that each parameter has a certain influence on the performance of the joint.(1)In the case of other welding parameters,the bypass current from 150 A to 180 A process,the weld width and penetration are reduced,while the excess weld metal is increased.and the grain size of the weld fusion zone is reduced by measurement.The microhardness of the welded joint shows a gradual increase in the process of increasing the bypass current.By drawing the welds obtained by different bypass currents,The tensile strength of the weld has been increased from the bypass current of 150 A to 180 A,and the tensile strength increases abruptly when the bypass current is 180 A.(2)The increase of welding voltage makes the weld weld width increase,the depth of penetration and excess weld metal decreases.When the welding voltage is 23 V,the weld shape is the best.While the grain size also increased,but the increase is very small,it can be considered basically unaffected.The microhardness of the weld fusion zone is basically the same,the tensile strength of the joint is slowly reduced,and when the voltage is 24 V,the weld is not penetrated and the tensile strength is increased.(3)welding speed from 2.3m / min to 2.9m / min welding process,the weld width and depth of penetration gradually reduced,and the excess weld metal from the welding speed of 2.3m / min began to increase till to the welding speed of 2.7m / min,and the change of grain size in the weld zone is the same as that of the bypass current.The results of microhardness test and tensile test show that the microhardness and tensile strength of the welded joint increase with the increase of welding speed.(4)The optimal welding parameters are obtained as follows: main current I = 230 A,bypass current I = 170 A,welding voltage U = 23 V,welding speed V = 2.7m / min.(5)The weld penetration and the excess weld metal increase with the increase of SiC to ρ = 5.64 mg / cm2,and decrease with the increase of SiC coating,but the change of the melting width is opposite.When the addition amount of SiC is less than ρ = 5.64 mg / cm2,it can play the role of grain refinement,and SiC particles can disperse β-Mg17Al12 in the weld.The addition of SiC particles effectively improves the microhardness of the welded joints,and the microhardness of the joints increases with the increase of the amount of SiC coating.With the increase of SiC coating,the tensile strength of the joint increases.However,when the SiC coating amount is greater than ρ = 5.64 mg / cm2,the tensile strength of the welded joint is obviously reduced.