Multi-scale Synergistic Mechanical Optimization Of Silver Alloy By Selective Laser Melting

Silver is one of the precious metal materials known and used by human beings in the early stage.In the industrial field,silver is an important material for smart electronics,green energy(e.g.photovoltaic)and modern communication(e.g.5G)equipment.In the field of people's livelihood,its application in the medical health,wearable and jewelry industries also meets people's aspiration for a better life.In 2019,the global annual production of silver was 31,821 tons,of which industrial demand for silver accounted for 52%.The annual exploitation of silver in China(3443 tons)is onetenth of that in the world,but the domestic industrial silver(3773 tons)alone accounts for one-fourth of the global industrial silver,and has exceeded the domestic annual exploitation.As a non-renewable precious metal material that plays an important role in industrial development and social livelihood,the efficient utilization and performance optimization of silver has become an urgent research topic.Silver has low mechanical strength and high ductility.Optimization of mechanical properties is an important way to improve the utilization rate of materials.Conventional silver mechanical properties optimization methods,such as solid solution strengthening,work hardening,heat treatment,etc.,can improve the mechanical strength to a certain extent,but there is a bottleneck for further efficient utilization and performance optimization.Adopting a precision manufacturing technology that can optimize mechanical properties and studying its corresponding precise control strategy is an important idea to break through the bottleneck.Laser selective melting technology,as an advanced manufacturing technology,has shown its advantages in mechanical strengthening,precision manufacturing,and multiscale precision control.Multi-scale control to achieve mechanical optimization is also the frontier and hot spot of laser selective melting technology.Different from common SLM metals,the challenges of high thermal conductivity to precise control,high cost to lightweight and high ductility to mechanical optimization of silver materials are representative in SLM research fields.However,the research on the effect of parameter control on the multi-scale properties of silver alloys is still a blank.There is an urgent need to investigate the multi-scale synergistic mechanical strengthening mechanism of the cube for the thermodynamic properties of silver alloys,the silver alloy lightweight technology applicable to SLM forming and the strategy of multi-scale synergistic mechanical optimization of functional structures based on the mechanical properties of silver alloys.Therefore,this paper proposes a multi-scale synergistic mechanical optimization of silver alloy based on SLM technology.Taking dense cubes and complex structures(lattice structure and negative Poisson's ratio structure)as the research objects,the mechanism of multifactor influence(topology,process and structural parameters)on multi-scale is revealed through multi-scale precise control.To establish multi-scale synergistic mechanical optimization strategies for dense cubes and complex structures.Lightweighting(lattice structure)and functionalization(negative Poisson's ratio structure)research is carried out based on the mechanical strengthening research of dense cubes.In the study,it was found that the unique directional solidification and extremely high thermal conductivity during the forming process of silver alloys can form a variety of unique microstructures(including submicron equiaxed grains),resulting in the preparation of high hardness silver alloy cubes(148.9 HV)that are three times higher than conventional castings.A multi-scale synergistic mechanical strengthening mechanism inspired by large-angle grain boundaries was established to achieve simultaneous enhancement of yield strength(+ 145%)and ductility(+28%)of dense cube materials.For the first time,the T-Splines algorithm was applied to optimize the macroscale topological structure design of complex structures,and the synergistic process parameters and structural parameters with fine dimensions were locally and globally control in multiple scales to achieve the control goals of efficient utilization(70 %max weight reduction in lattice structure relative to cube material)and performance optimization(high compressive strength(7.8-fold increase compared to control groups),isotropic(1.06 %min),high negative Poisson's ratio(-0.51))of complex precision structures.