The Investigation Of Metallurgical Characterization And Configuration Optimization Of Wire Arc Additive Manufacturing AZ80M Magnesium Alloy

Magnesium alloy has the characteristics of low density,high specific strength/specific stiffness,good damping,excellent electromagnetic shielding performance and abundant domestic resources,which is called "the green engineering material of the 21 st century".It has a wide application prospect in the fields of automobile,aerospace,rail transit and electronic3 C equipment manufacturing.The traditional machining methods of magnesium alloy are mainly die casting and deformation machining.Die-cast magnesium alloys are widely used,but their applications in lightweight key parts are limited due to their low mechanical properties and poor corrosion resistance.The mechanical properties of wrought magnesium alloys are excellent,but due to the difficulty of forming and low production efficiency,the existing application scale is very small.Wire arc additive manufacturing(WAAM)is a hot research topic in metal 3D printing recently.WAAM technology uses welding arc to deposit metal layer by layer,and finally forms metal parts with definite shape and dimensional accuracy.It has the characteristics of fast deposition speed,high material utilization rate,unrestricted processing size and shape,etc.,and is suitable for the rapid manufacturing of metal parts with large size and low complexity.In order to explore the applicability of WAAM to the manufacturing of magnesium alloy parts and develop high-value application scenarios,the forming process of WAAM-AZ80 M was systematically studied in this paper,and a multiple regression model between the process parameters and the forming size was established.The formation and evolution of the deposited microstructure were characterized,and the applicability of different post-heat treatments on the microstructure and properties of WAAM-AZ80 M was verified.By means of finite element simulation and phase field calculation,the evolution characteristics of the WAAM cycle temperature field on the microstructure were revealed,which provided a new idea for the further online microstructure regulation.The microstructure and properties of WAAMAZ80 M were optimized by means of metal deposition,rolling with welding and post-heat treatment,and the strengthening mechanism was summarized and analyzed.Specific findings include:Based on the variation characteristics of the width of WAAM-AZ80 M single-pass multilayer parts,it is divided into: the bottom width variation zone,the middle stability zone and the top arc zone.The thermal field changes from unsteady state to stable state and the change of the morphology of the deposition layer reflects the arc heat loss path.By using quadratic general rotary unitized design method to design the test sample,has established the main four process parameters(peak current Ip,welding speed Vw,wire feed speed Vf and interlayer temperature T)and layer width and the height of the regression model,model for the analysis of variance,respectively,the results show that the fit of the regression equation is good.Further analysis shows that Vw has the most significant effect on the layer width,and the interaction between Vw and T has an effect on the layer width.Vf has the most significant effect on the layer height,and the interaction between Vw and Ip,and between Vw and T has an effect on the layer height.WAAM-AZ80 M single-pass multilayer deposition parts have obvious microstructure heterogeneity and layered characteristics.During the deposition process,the eutectic structure was dissolved due to the influence of unsteady thermal cycle,and the microstructure within the top arc zone transformed into the middle region,gradually.The microstructure at different locations in the same layer are not uniform due to the difference of cooling rate.The mechanical properties of WAAM-AZ80 M are between the as-cast and extruded AZ80 M,and there is anisotropy.Several typical heat treatment processes have different effects on WAAMAZ80 M.T4 heat treatment improves the plasticity of the deposited parts.T5 heat treatment maintains the coarse eutectic structure in the deposition state,and the precipitated phase has the phenomenon of segregation.After T6 heat treatment,the grain refined,and the precipitated phase is more uniform.The strength and plasticity after T6 are improved,and the anisotropy of properties is weakened.The temperature field simulation of WAAM-AZ80 M shows that in the initial layers of the deposition,the temperature field along the deposition direction and perpendicular to the deposition direction gradually enters the stable state.When the temperature field enters the stable state,the thermal cycle process at the same position in different layers has a stable repeatability.Based on the theory of diffuse-controlled solution-type phase transition,the dynamics model of the second phase dissolution in the arc deposited AZ80 M was established by DICTRA software and its accuracy was verified.Coupling the thermal cycle curve of finite element simulation with the established kinetic model of the second phase dissolution,it was obtained that the volume content of the second phase in WAAM-AZ80 M process decreased step by step with time,and there were dissolution and micro-precipitation of the second phase under the same temperature cycle.In WAAM-AZ80 M process,rolling along with deposition is introduced,which can break the coarse equiaxed dendrites.With the increase of rolling force,the recrystallization and grain refinement effect are enhanced.Grain refinement and work hardening are the main strengthening mechanisms.Compared with the as-deposited sample,the dissolution degree of the second phase in the deposited metal after rolling along with deposition is higher,and the inhomogeneity between layers is improved.After 4k N rolled,the mechanical properties of the deposited parts are improved obviously,especially along the vertical direction.Because the eutectic structure in the original structure was broken and refined with rolling,and could be completely dissolved,the precipitation of the alloy was more uniform in the subsequent T6 treatment,and the properties were further improved.Precipitation enhancement is the main strengthening mechanism after T6 treatment.