Investigation On The Process Of Aluminum Alloy Cellular Lattice Structure Fabricated By Selective Laser Melting

Selective laser melting(SLM)has the capacity to produce advanced-performance metal cellular lattice directly from computer-aided design data and metal powders.However,cellular lattice structure with high surface quality and dimensional accuracy as well as homogeneous microstructure can hardly be obtained by SLM technology due to the dramaticly changed scanning area of node and various force situation of molten pool,heat history through the strut.Until now,few works have been addressed on this topic.In this paper,a systematic investigation on the fabrication of Al Si10 Mg cellular lattice structure using SLM technology has been carried out.The main results are listed as follows:(1)Matlab-based program was established to measure relative density,surface roughness and size of strut from optical microscope image fast and acuurately.The experimental results show that the method is feasible.(2)The influence of processing parameters on the defect,relative density,surface roughness and dimensional accuracy was investigated.It was found that reducing the layer thickness can enlarge the process window and improve down-warding surface quality.Besides,the up-warding and down-warding surface roughness show different trends with the changing of processing parameters.Further increasing the scanning speed,the uneven distributed defects were eliminated and the difference of molten pool morphology in different zones is reduced.In addition,the dimensional accuracy can be improved.The reason can be attributed to that the solidfying rate and molten pool is small under high scanning speed,inhabiting the over-compensation effect.Through the comprehensive evalution of forming quality,the optimal process parameters are determined as follows:laser power is 200 W,layer thickness is 20?m,scanning speed is 1400~3000 mm/s,hatch spacing is 0.04~0.10 mm.(3)The struts with different inclined angle and size were manufactured using optimal parameters to investigated the influence of geometrical feature on the forming quality of cellular lattice structure.The results indicate that strut with inclined angle of 10°can still form well.The heat accumulation effect and loss rate are closed related to strut size,leading to the relative density and dimensional accuracy are slightly lower.But the surface roughness poorly depends on strut size.(4)The microstruture evolution in differents zones of the strut and node was firstly investegated.Results shown that the microstructure in different zones has various characters under a low scaning speed.Eutectic Si distribute sparsely and the width of coarse cellular region is largest in powder-supported zone(PZ).The non-homogenous microstructure through the strut can be reduced by further increasing the scanning speed.The relative contents of Eutectic Si increased.Netlike or interdendritic eutectic Si transformed into granular shape.In addition,there are a lot of sub grain boundary in PZ.The Al,Si and Mg elements distribute uniformly in the struts.The eutectic Si in the bottom of node are little sparse.(5)Induced by the significantly different characteristic microstructure throughout the SLMed strut and node,the microhardness are nonuniform under low scanning speed.Increasing the scanning speed,the microhardness of SLMed strut and node improved and gradually becomes uniform.When the scanning speed of 3000 mm/s is applied,the average microhardnerss of struts and nodes were measured to be 157±3 HV and 161±10HV respectively.Besides,the compress stress of SLMed cellular lattice structure with volume fraction of 7.5% is 58.43 MPa.