Study On Microstructures And Mechanical Properties Of Aluminum Alloy Produced By 3D Printing

In the recent years,the developing 3D printing technology enormously has developed the design and manufacture space of components and fully embodies the technical advantages of flexible design in additive manufacturing.As a representative technology of 3D printing rapid prototyping processes,selective laser melting has prominent advantages of high surface accuracy,high stock utilization,short production cycle and conducive to innovative structure design.SLM is an effective way to process aluminum alloy and lightweight structural parts.However,due to the powder preparation,molding process,and the subsequent processing have not been fully connected,the metallurgical defects of hot crack,balling,and pores are easily to be produced.To explode the above problem and to improve the mechanical properties of AlSi10Mg with no easily cracking,which is widely used in 3D printing technology,the method of optimizing process parameters and heat treatments are adopted in this paper.The main content of this article has the following points:（1）Firstly,with optimized parameters,AlSi10Mg alloy with good mechanical properties and high relative density of 99.7%was obtained by selective laser melting（SLM）.The results show that the laser scan speed has a bigger influence on the density of SLM samples than the laser power.With the decreasing of laser scan speed,the linear energy density was increasing gradually,resulting in the improving of the density of SLM samples.However,the solidification rate was increased under the higher laser scan speed and lower laser power.And the higher solidification rate resulted in the formation of supersaturated solid solution Si and net-work Si in α-Al and improved the mechanical properties of SLM AlSi10Mg samples.With optimized parameters,AlSi10Mg alloy has excellent ultimate tensile strength and hardness.The SLM sample was～479 MPa in ultimate tensile strength,～8%in total elongation along horizontal direction and～122 HV in average hardness along the building direction.There is no apparent change of hardness on different building heights.However,the mechanical properties had the performance anisotropy,it was lower on the building direction than that on horizontal direction.The ultimate tensile strength and the elongation along building direction were 397 MP and 6.4%,respectively.（2）Secondly,to further improve the comprehensive performance on the building direction of AlSi10Mg alloy with the supersaturated solid solution Si and net-work Si in α-Al formed by laser selective melting,aging heat treatment was adopted in this study.The effects of aging on microstructure and mechanical properties on the building direction of AlSi10Mg samples produced via selective laser melting（SLM）were systematically investigated.The results showed that directly aging could retain the fine structure of SLM parts,control the precipitates effectively,and homogenize the microstructure.With the combination of solution strengthening,microstructure refinement,and precipitation strengthening,the mechanical properties along the building direction of the SLM sample were prominently improved.Although some micronsized pores were found after aging treatments,the optimized mechanical properties were obtained after aging at 130℃.The tensile strength,ductility,and microhardness were improved by 13%,47%,and 10%compared to the as fabricated sample,respectively.（3）Finally,to achieve homogeneous microstructure and to further improve the elongation of the SLM samples,the effect of heat treatments on the microstructure and mechanical properties of the SLM sample along the horizontal direction was analyzed.After heat treatments,the strength of the samples showed major differences,while the elongation was significantly improved.After solid solution treatment at 540℃ for 1 h,the UTS was significantly decreased to about 246 MPa and the elongation was increased to more than 22%.After annealing at 236℃ for 10 h,the UTS was about 368 MPa and the elongation was about 17%.It should be noted that after ageing at 130℃ for 4 h,the sample showed high strength with the same level of the SLM sample;moreover,the elongation of the aged sample was increased to about 11.9%.The hardness was about 133 HV which was 10%higher than that for the SLM sample.The improved performance of the aged samples can be attributed to the combination of solution strengthening,microstructure refinement,and precipitation strengthening.Clearly,for SLM sample with fine microstructure,low temperature ageing is the optimized heat treatment method.