Microstructure And Mechanical Properties Of Cold Metal Transfer Based Wire And Arc Additive Manufacturing AZ31 Magnesium Alloys

Magnesium alloy,as the most potential light metal structural material for application,has the advantages of high specific strength,high specific stiffness and good damping capacity,which helps to realize the light weight in the industrial field.Whereas magnesium alloy has poor plastic deformation ability,and there is many difficulties in forming using traditional casting and forging technology,thus it unable to meet the manufacturing needs of components with large size and complex structure in industrial field.Wire-arc additive manufacturing(WAAM)technology has the characteristics of low cost and high efficiency,particularly the cold metal transfer(CMT)welding arc with low heat input characteristics is helpful to realize the additive manufacturing of large-size magnesium alloy components.Therefore,this paper is based on the CMT welding power source and uses AZ31 magnesium alloy wire to conduct basic research on the application of WAAM magnesium alloy.Experiments were designed to study the forming quality,microstructure and mechanical properties of AZ31 alloy weld bead and thin wall by varying the weaving arc parameters and welding speed in WAAM.The forming quality and mechanical properties of AZ31 complex parts made by WAAM under the optimal parameters were investigated.The main conclusions are as follows:(1)The weaving arc can improve the forming quality of thin wall in the arc additive manufacturing of AZ31 magnesium alloy.Proper arc weaving parameters can effectively increase the fluidity of the melt pool,improve the width to height ratio and reduce the contact angle of weld bead specimens,at a weaving width 10 mm weaving length 4 mm,thin wall forming quality is best.The amount of cladding can be changed by adjusting the welding speed.In welding speed 5 and 7 mm/s thin walls can be formed smoothly,while welding speed 3,9 and 11 mm/s cannot be formed.(2)The microstructure of specimen consists of three regions with different grain sizes under thermal cycling,namely the deposition zone,remelting zone and heat affected zone.The weaving arc enhances the stirring effect of the molten pool and increases the cooling rate,resulting in grain refinement,and 12.3%and 13.9%reduction in grain size in the deposited and heat affected zones can be obtained,respectively.Increasing the welding speed decreases the heat input,and the grain size in the deposition zone decreases by 47.5%when the welding speed increases from 3 to 7 mm/s.(3)Adjustment of the weaving arc parameters can eliminate anisotropy in the mechanical properties of thin wall.in the weaving width of 10 mm weaving length of 4 mm parameters,the construction direction of the tensile strength and elongation relative to no weaving arc increased by 6.2%and 60%,respectively.The tensile strength and elongation were optimal at a welding speed of 7 mm/s.At a welding speed of 9 mm/s the elongation was 12.5%,which was nearly 50%lower compared to the specimen with a welding speed of 7 mm/s.(4)In the material 1.2 mm AZ31 magnesium alloy wire,parameters for the wire feed speed 9 m/min,current 100 A,voltage 14.3 V,swing width 10 mm swing length 4 mm,welding speed 7 mm/s under the conditions,optimized forming quality,minimum grain size,optimal mechanical properties and no anisotropy of the thin wall can be obtained.The tensile strengths in the building and traveling directions are 239 MPa and 239 MPa,respectively,and elongation is 24%and 25%,respectively.(5)Multi-pass multilayer specimens,high thin wall and complex cylindrical parts can all be fabricated with AZ31 alloy by WAAM.The forming quality of multi-pass multilayer specimens is poor and the optimization of the path and torch angle is required to obtain better forming quality.The mechanical properties of multi-layer specimens are isotropic in three directions,i.e.building direction,traveling direction and connection direction.