Research On The Scale Effect Of SLM Forming Of Lightweight Characteristic Structures Of High-strength Aluminum Alloy Spacecraf

Aluminum alloy is widely used in aviation and aerospace industry.High-strength aluminum alloy has higher specific strength than conventional aluminum alloy,which is more suitable for the application of lightweight structural parts of spacecraft to enhance the strength.Selective Laser Melting(SLM)is a metal 3D printing forming technology.The metal products are characterized by high density,stable microstructure and excellent mechanical properties.The SLM process have advantages for the forming of lightweight thin-walled and weakly rigid aerospace components filled with internal lattice.In the forming process,the adjustment of technological parameters and the control of shaping size become the main factors of its application.Therefore,it is of great significance to study the multi-factor scale effect of SLM for the skin lattice structure of high strength aluminum alloy.Aiming at Al-Mg-Sc-Zr high-strength aluminum alloy material,the paper studies process parameters effects of SLM on the forming density,microstructure and mechanical properties through experiments,obtains the optimal process parameters of Al-Mg-Sc-Zr high-strength aluminum alloy as follows:The laser power is 360W,the hatch distance is 80μm,the scanning speed is 1100mm/s,the powder layer thickness is 30μm,and the physical density is136.36J/mm~3.Under these parameters of SLM process,the yield strength of the depositional sample is kept in the range of 328～347MPa,and the tensile strength is 355～369MPa,elongation in the range of 15.1%～20.6%.On this basis,the effect of annealing scheme on the microstructure and properties of Al-Mg-Sc-Zr alloy is studied.The experimental results show that after being held at 325℃for 4h,the crystal morphology of Al-Mg-Sc-Zr high strength aluminum alloy SLM samples is more regular,the grain size is more uniform,the grain boundary clarity is improved,and the grain distribution is more compact.At this time,the mechanical properties of the sample are the best.The yield strength ranges from 501～506MPa,the tensile strength ranges from 507～525MPa,and the elongation ranges from 10.9%～12.7%.Based on the process parameters and annealing optimization results,the size effect between thin-wall structure and skin lattice structure was investigated.The size effect phenomenon of skin lattice structure was characterized in terms of mechanical properties,including tensile/compressive strength,yield strength and elongation.The mechanical experiment results of thin-wall and skin lattice structure show that the size effect is influenced by the factors of size,forming accuracy and direction of forming.Among which the size has the greatest influence,the forming orientation follows,and the forming accuracy has the least influence.According to the results of the skin lattice structure test,a mathematical model between the actual forming size and the laser spot diameter,the width of the molten pool and the error factor of incomplete fusion was established,which could be used to adjust and control the compensation of laser spot and save the cost of testing and debugging.