Study On Bypass-Current Plasma MIG Process Of Marine Aluminum Alloy

With the rapid development of the shipbuilding industry,people have put forward higher and higher requirements for the environmental protection,energy saving,corrosion resistance and service life of ships.However,traditional shipbuilding materials are difficult to meet these requirements due to their material properties.Aluminum alloy has been widely used in the shipbuilding field due to its low density,strong corrosion resistance,high specific strength and specific modulus,which can greatly reduce the weight of the hull,reduce fuel consumption and improve the service life of the ship.However,the aluminum alloy has the problem of welding.The widely used MIG/TIG welding method has poor welding quality and low efficiency,which seriously restricts the wider application of aluminum alloy in the marine field.Therefore,it is of great significance to study the new welding process for aluminum alloy welding to promote the development of China's shipbuilding industry.Aiming at the welding characteristics of aluminum alloy,a new process of Bypass-Current Plasma MIG welding is proposed.The new process is to shunt a part of the welding current through the base metal by using an arc generated between the plasma torch nozzle and the wire as a bypass during the plasma-MIG welding,which can not only exert the advantages of the plasma-MIG welding,but also achieve good welding heat input control.In this paper,a new type of welding torch was designed and manufactured for this new process.A welding test platform was built and the new test was applied to the welding test of 6mm and 2mm thick 5083 aluminum alloy.The effects of different process parameters on weld formation were investigated.The electrical signals and droplet transitions in the welding process were tested to establish their internal relationship with welding stability and weld formation.The effect of bypass current on reducing heat input was studied.Moreover,the microstructure analysis and mechanical properties of the obtained welded joints were tested.The research results show that under the suitable welding parameters,the new process can realize single-side welding double-sided forming of medium-thick(6mm)aluminum alloy plates and high-speed welding of thin(2mm)aluminum alloy plates.The obtained butt joint has a high strength,and the average tensile strength thereof is 285 MPa,which is at or near the strength of the base material,and the fracture form is ductile fracture.During the welding process,the observed droplet transition mainly has short-circuit transition and droplet transition.When the short-circuit transition occurs,the bypass current is unstable,there is a large welding spatter,the weld seam is poorly formed,and the current fluctuation occurs during the droplet transition.Smaller,the droplet transfer is stable and good weld formation can be obtained.The bypass current has a significant effect on stabilizing the arc and reducing the welding heat input.When the main circuit current is constant,the bypass current is increased,and the current through the base material is reduced.At this time,the cathode heat generation of the base material is reduced.As the welding heat input is reduced,the depth and the width of the weld is significantly reduced.Bypass-Current Plasma MIG Process can not only improve the welding efficiency,but also ensure the joint quality,which provides a new idea for the welding of aluminum alloy.It has great research and practical value to promote aluminum alloy.The application in the field of ships is of great significance.