Research On High-Efficiency Selective Laser Melting Process For AlSi10Mg Alloy Powder With Large Layer Thickness

Selective laser melting(SLM)process has great advantages for metal powder forming.It is not only convenient for the forming of complex parts,but also has better performance than castings.It is widely used in the preparation of complex structure and functional parts.At present,the thickness of SLM forming layer is mainly concentrated in the small layer thickness range of 20μm～40μm,and the forming efficiency is not high.There is an urgent need for the development of SLM forming process with large layer thickness.In order to shorten the production cycle and improve the production efficiency,the forming process of AlSi10Mg alloy SLM with large thickness was studied in this thesis.Firstly,the single molten pool sample and bulk sample were studied with the thickness of40,80,120μm deposition thickness,and the process parameters of AlSi10Mg formed by SLM with large thickness were developed and optimized.The results show that with the increase of laser power,the energy inputΨ_δincreases immediately,and the wetting quality of the single-channel molten pool is better.With the increase of scanning speed andΨ_δ,the wetting quality of the one-channel molten pool is worse.So that the density is the optimization objective,and the optimal process parameters corresponding to each layer thickness are obtained.Secondly,the microstructure and quality of AlSi10Mg alloy formed by SLM with different thickness were studied.The results show that with the increase of the thickness of the deposition thickness,the microstructure size,quantity and morphology of the transverse and longitudinal sections change,and the network Al-Si eutectic microstructure of the longitudinal section is gradually fractured and aggregated.The major diffraction peaks of Al in the 40μm and 120μm samples shifted to the right compared with those in the AlSi10Mg powder and the80μm and 120μm samples.Combined with the EDS analysis of the tissues,it was found that some Si was precipitated in the 80μm and 120μm layers.Compared with the tensile properties of the national standard cast samples,the minimum tensile properties of SLM with different sediment thicknesses increased by more than 60%,and the fracture morphology also changed with the increase of the thickness.The hardness of the upper and side surfaces decreased with the increase of the thickness of the deposit layer,and the hardness of the side surface with the thickness of 120μm decreased greatly.With the increase of layer thickness,the porosity rises slowly at first and then increases sharply.The porosity of 120μm layer thickness is about 4times that of the first two layers,and the pore distribution of industrial CT is basically consistent with that of industrial CT.With the increase of layer thickness,the surface roughness also increases.The upper surface roughness of 120μm layer thickness exceeds the instrument range.Finally,the simulation and printing experiment of the pump impeller with complex profile were carried out with the optimum process parameters of each layer thickness.The simulation results show that the residual stress and deformation of the forward placement scheme decrease with the increase of the deposition thickness.The maximum residual stress of the forward placement scheme is less than the yield strength of the material,and its maximum deformation is less than 30~°.The forward placement scheme can be used for actual printing.The results of printing experiment found that:With the increase of the thickness of the printed deposit layer,the appearance and surface quality of the impeller gradually deteriorated,but no cracks and warping deformation were found in the printed impeller and the whole support.The results of the three coordinate measurement show that the simulation of the forming process can accurately predict the changing trend of the maximum deformation under different thickness of the deposit layer,and the numerical simulation based on the inherent strain method can better predict the actual printing effect of SLM.According to the forward scheme obtained by the simulation of SLM forming process with three layers thickness,it is found that the forming rate increases by 91%and the production efficiency increases by 45%when the layer thickness increases from 40μm to 80μm,but the improvement is not obvious when the layer thickness continues to increase.No cracks or holes above 200μm were found by X-ray detection of the impeller printed with each layer thickness.Combined with the tolerance level of the impeller parts obtained by laser scanning reverse modeling deformation detection,the process parameters of large layer thickness of AlSi10Mg powder SLM was finally confirmed.