Research On Characteristics Of Helium Arc And Numerical Simulation For Form Of Molten Pool In 2219 Aluminum Alloy

In the field of aeronautics and astronautics,welding of the fuel tank in large launch vehicles has been difficult.A new welding process is proposed to solve the problem in the welding of 2219 aluminum alloy thick plate: helium tungsten-arc welding to float bottom and argon tungsten-arc welding to fill.Welding 10 mm thick 2219 aluminum alloy plate doesn’t need to prepare the groove and weld forming once.And the molten pool doesn’t collapse without a back.The weld quality is better and the hole defect is significantly reduced.The study of experiment and numerical simulation was carried on to illuminate the difference of the forming and weld quality of helium tungsten-arc weld and argon tungsten-arc weld.Comparative research of helium and argon arc characters was carried on to study heat source model that influences molten pool heat input and force source model that influences molten pool reaction and provide experimental data and theoretical basis for numerical simulation of molten pool form in helium tungsten-arc weld and argon tungsten-arc weld.The shape of helium arc is round and its anode is in contraction,the shape of argon arc is the bell shape and its anode is diverging.What’s more,the arc pressure of helium arc is smaller than argon arc.And the molten pool of helium tungsten-arc weld avoids collapsing without a back.What’s more,the power density distribution of helium arc anode is more concentrated than argon arc,which can increase weld depth and improve the depth to width ratio.Numerical simulation for form of molten pool in helium tungsten-arc welding was carried on to analyze the differences in the form of molten pool helium tungsten-arc welding and argon tungsten-arc welding and study the effect of different welding parameters on the form of molten pool in helium tungsten-arc welding.Compared with argon tungsten-arc welding,the width of molten pool front in helium tungsten-arc welding is smaller,and deep penetration is larger.It can improve the depth to width ratio of molten pool.As the welding speed increasing,the arc characteristics remains the same and the time of molten pool heat input and the reaction each grid decreases.So the width of molten pool front decreases slightly,the width of molten pool back decreases obviously and the amount of collapse decreases.As the welding current increasing,the maximum value and the distribution radius of arc anode power density increases so the width at molten pool front increases.The electromagnetic and arc pressure increases so the width of molten pool back increases sharply and the amount of collapse increases.As the length of arc increasing,molten pool heat input increases so the width of molten pool front remains same,the width of molten pool back increases and the amount of collapse increases.As the arc pressure increasing,the width of molten pool front decreases,the width of molten pool back increases and the amount of collapse increases sharply.Comparing weld forming and the organization and performance in helium tungsten-arc welding with argon tungsten-arc welding to study weld forming and quality.As the welding current increasing,the width of molten pool back increases more sharply in helium tungsten-arc welding,and the width of molten pool front increases more sharply in argon tungsten-arc welding.When the width of molten pool back reach to the same,the width of molten pool front in helium tungsten-arc welding is more narrow than argon tungsten-arc welding,the amount of collapse is smaller and the width of heat affected zone and fusion line are more narrow.The micro-structure and second phase organization of them are same.Grain shapes in weld area are isometric.And in heat affected zone,grain shapes are coarse stripes and organization are the ? aluminum substrate with Al2 Cu inter-metallic compound and a few eutectic tissue and a lot of welding balls were found.What’s more,the amount of the second phase organization in weld area is larger than heat affected zone.The welds in helium tungsten-arc and argon tungsten-arc are ductile fracture and the tensile strength of them are the same.The elongation and hardness of weld in helium tungsten-arc welding is higher.