Laser Selective Melting Forming And Mechanical Properties Of Magnesium Alloy Lattice Structure

Magnesium alloy has the characteristics of low density,strong shock absorption,high specific strength,high specific rigidity,good electromagnetic shielding and biocompatibility.It has a wide range of applications in aviation,aerospace and other fields with high requirements for lightweight.Selective laser melting is a new additive manufacturing technology in recent years.It has technical advantages in forming complex structural parts.The combination of selective laser melting and light metal magnesium alloy can further promote the lightweight design of aerospace structural parts and realize the lightweight upgrading of new generation aerospace products.In this paper,the structure optimization design of conventional selective laser melting additive manufacturing equipment was carried out to meet the additive manufacturing requirements of magnesium alloy materials.AZ91 D magnesium alloy spherical powder was used as raw material for additive manufacturing,and the improved SLM laser selective melting equipment was used for additive manufacturing of AZ91 D magnesium alloy powder.In this paper,the additive manufacturing process,microstructure,mechanical properties and lattice structure of magnesium alloy were studied,and the lattice structure optimization design and printing verification of typical aerospace structures were carried out.The main research work and conclusions are as follows:(1)The structure of powder dropping and powder spreading mechanism of conventional SLM additive manufacturing equipment was optimized,and roller brush powder structure and rubber scraper powder spreading structure were designed according to the characteristics of magnesium alloy material,which effectively realized the uniform powder dropping and dense powder spreading function of magnesium alloy powder.The average deviation of powder feeding was within ± 0.1g,and the increase rate of powder spreading density was25.57%.At the same time,99.999% powder feeding method was adopted High purity argon as a protective gas,the oxygen content in the molding cavity can be controlled below100 ppm stably,which can effectively inhibit the generation of a large number of smoke and dust,and realize the timely discharge of smoke and dust in the molding process through argon laminar flow.(2)The main processing parameters of laser selective melting of AZ91 D magnesium alloy,such as scanning distance,scanning speed and laser power,were studied by orthogonal experiment.The results show that the suitable processing parameters are scanning distance-0.06 mm,scanning speed-600 mm / s and laser power-200 W,and the forming density can reach 98.7%.At the same time,it is found that the filling spacing has an important influence on the laser selective melting of magnesium alloy.The parameters of filling spacing should be about 0.06 mm,and the density of the molded parts will decrease sharply when the filling spacing exceeds 0.1mm.On the premise of keeping the filling spacing constant,with the ratio of power to scanning speed increasing gradually,the density of the molded parts will increase first and then decrease The microstructure of AZ91 D magnesium alloy formed by selective laser melting was observed,and the grain size is about 2um,which is much smaller than that formed by casting.(3)The mechanical properties of AZ91 D Magnesium Alloy by selective laser melting were studied.The optimum tensile strength is 292 MPa and the maximum elongation after fracture is 3.81%.Through the single factor variable test,it is found that the mechanical properties of tensile specimens increase gradually with the increase of laser power when the filling distance and scanning speed remain constant,but decrease when the laser power exceeds a certain value;when the filling distance and laser power remain constant,the mechanical properties of tensile specimens decrease gradually with the increase of scanning speed When the laser power and scanning speed are kept constant,the mechanical properties of tensile specimens increase gradually with the increase of filling distance,but decrease when the laser power and scanning speed exceed a certain value.At the same time,the fracture surface of the tensile specimen was detected and analyzed,and it was found that the fracture surface presented a ductile brittle mixed fracture morphology.There were a large number of tiny voids and incomplete melting areas in the specimen.These voids and incomplete melting areas gradually developed into cracks and expanded under the effect of tensile force,which led to the fracture of the specimen,so the elongation after fracture of the specimen was low.(4)Based on the laser selective melting technology,the forming test of AZ91 D magnesium alloy lattice structure is carried out.The maximum standard compressive strength of the lattice structure can reach 181.550 MPa and the weight reduction is 70.243%.The lattice structure is applied to lightweight design and forming of typical space shell structure.The compressive bearing test is carried out with the solid structure shell with the same magnesium alloy material volume.It is found that the maximum compressive capacity of lattice shell with 1mm skin can reach 76.667% of the maximum compressive capacity of the shell.