Microstructure And Mechanical Properties Of AZ31 Magnesiμm Alloy Deposited By Electron Beam Wire Fusing Deposited

The electron beam additive manufacturing technology has been developed and applied in recent years.The heat source is an electron beam,processed in a vacuum chamber,and a predetermined structure is established by layer stacking.Magnesium and magnesium alloys are densely packed hexagonal crystal structures with few independent slip systems and difficult deformation.the study of magnesium alloy electron beam fuse deposition is of great significance for expanding the application of magnesium alloy in aerospace,defense military,electronic device housing and other fields.In this paper,AZ31 magnesium alloy wire used as the printing material,and pure magnesium is used as the substrate.Research shows that the beam current and wire feeding speed have a significant influence on the formability of the printing block.When the beam is too large,a stable molten pool cannot be formed;when the beam is less than 15 mA,the energy input will not melt the AZ31 wire.The wire feeding speed has a minimum value with respect to the beam current.When the wire feeding speed is less than this critical value,the trailing wire material is softened,resulting in a decrease in formability.The 20 mA beam and the 2500mm/min wire feed speed were selected as the optimized process parameters for AZ31 wire printing.Microstructures at different energy densities show that as the energy density decreases,the average grain size of a single pass print decreases from 49 μm to 32 μm and The density of prints increased from 98.3% to 98.8%.Finite element simulation results of temperature show that,as the print number of layers increases,cooling mode is converted into thermal radiation from the substrate and the deposited layer heat transfer.The single-pass and multi-pass printing results of the optimized process showed that the microstructure was uneven along the construction direction,and the surface of the printed microstructure was fine.After the corrosion agent slightly corroded,a uniformly distributed fish scale-shaped molten pool line can be seen on the macroscopic surface,and fine eqiuaxed crystals appear at the microstructure of the fish-scale molten pool line.Larger grains appear inside the fish scales.The hardness difference between different grain size regions is obvious.Within the multi-pass block scale-shaped pool line,the grain size decreases from 38μm to 23μm along the build direction.It is proved that the complex thermal history caused by multiple re-melting is the main reason for the grain size growth.The presence of a submicron grain on the original large-sized grain is characterized by energy spectrum.The submicron grain mainly exists in the form of α-Mg and β-Mg17Al12.The complex thermal history of the printing process results in the presence of a diffuse distribution of nanoscale precipitates on the substrate.The multi-pass printing block has a 50% increase in yield strength and a 40% increase in tensile strength compared to the as-cast AZ31.The main strengthening modes of the multi-pass block are fine grain strengthening,solid solution strengthening and dispersion strengthening.The multi-pass block was heat-treated,and the microstructure homogenization effect was obvious at 350°C for 8 h,the grain size did not grow significantly,and the size and number of the second phase decreased.Hardness and mechanical properties did not have a obviously change.In summary,the AZ31 electron beam fuse deposition samples was successfully prepared in this paper,and the relationship between its microstructure change and mechanical properties.