Basic Research On Selective Laser Melting Additive Manufacturing Process Of NZ30K Magnesium Alloy

Additive manufacturing technology is rapidly changing traditional production and lifestyle.The traditional magnesium alloy manufacturing method has a long development cycle,poor performance and dimensional stability,and it is difficult to meet the needs of high-performance magnesium alloy complex fine components in the aerospace,biomedical and other fields.To this end,this paper takes Mg-3Nd-0.2Zn-Zr(wt.%,NZ30K)magnesium alloy selective laser melting(SLM)additive manufacturing technology as the research object.The microstructure and mechanical properties of NZ30K magnesium alloy solid block and porous implant and the effect of subsequent heat treatment.The main conclusions are as follows:The optimized SLM forming process parameters of NZ30K magnesium alloy are:laser power P=80W,powder layer thickness t=20?m,scanning speed v=225mm/s,scanning spacing HS=45?m.Under this process,no obvious macro-crack NZ30K magnesium alloy solid block sample,the density can reach 99.46%.The NZ30K magnesium alloy prepared by SLM is made up of fish scale-like small molten pools.The inside of the molten pool is composed of columnar crystals grown in the building direction,fine crystal regions,and elongated rare earth-rich oxide inclusions.There are lamellar microstructures distributed between?-Mg and Mg-Nd phases inside,and the crystal grains in the fine-grained area are fine and a large number of Zr-rich particles are distributed.Under the optimized process,the mechanical properties of SLM-NZ30K magnesium alloy at room temperature are yield strength 246MPa,ultimate tensile strength 261MPa,and elongation 3.7%.After a short-term high-temperature solution treatment,the grains are significantly coarsened,and a large amount of Nd H₂ phases appear inside the grains and at the grain boundaries.The strength and plasticity of the alloy at room temperature are significantly reduced.The direct aging treatment(T5)of SLM-NZ30K magnesium alloy can significantly improve the yield strength and tensile strength of the alloy,while significantly reducing the room temperature plasticity of the alloy.After T5 treatment,the highest strength of SLM-NZ30K magnesium alloy can reach:yield strength 380MPa,ultimate tensile strength 406MPa,elongation 0.9%.SLM technology can be used to manufacture NZ30K magnesium alloy porous implant without obvious macro cracks.The internal microstructure of the porous implant is significantly different.The coarse grains are dendrites with a grain size of?20?m,and the fine grains are equiaxed grains with a grain size of?2?m.The room temperature compressive properties of NZ30K magnesium alloy printed porous implants are:yield strength 71±4MPa,ultimate compressive strength106±6MPa,and elastic modulus of 3.5±0.5GPa.After a short-term solution treatment,the rare earth hydride in the porous implant increased significantly,the room temperature compression performance decreased significantly,and the corrosion resistance decreased.