Control Of Microstructure And Mechanical Properties Of AlSi10Mg Alloy Prepared By Selective Laser Melting

Aluminum alloy with high specific strength,light weight,good wear resistance and other advantages are widely used in aerospace,automotive,shipbuilding and other fields.With the increasing demand for complex and lightweight parts,the traditional manufacturing methods can not meet the needs of development.Selective Laser Melting(SLM)technology has great advantages in the preparation of complex structures,small batch production and customized parts due to its advantages of no mold,short cycle,rapid forming of complex parts and high forming accuracy.It is one of the most mature additive manufacturing(AM)technologies.Compared with other aluminum alloy powders,AlSi10 Mg alloy powders have the advantages of good fluidity,small shrinkage rate and small hot cracking tendency,etc.,and are more suitable for SLM forming.Therefore,AlSi10 Mg alloy powders have attracted the attention of many research institutions at home and abroad.At present,the research on SLM forming AlSi10 Mg alloy is mainly focused on improving the forming quality of parts,but the research on the microstructure evolution of molten pool during forming process and the crack initiation and propagation during tensile process is not enough.Based on this,the microstructure of AlSi10 Mg alloy was controlled from three aspects,namely laser forming strategy,heat treatment and nano-reinforcement,and the effect on mechanical properties was studied in this paper.In this paper,two forming strategies(zigzag-90 and zigzag-67)were used to compare the deposition microstructure and mechanical properties of SLM AlSi10 Mg alloy,to clarify the evolution process of the non-uniform microstructure at the molten pool boundary,and to discuss the initiation and propagation of cracks in the tensile process.Then the microstructure and mechanical properties of the deposited AlSi10 Mg alloy were regulated.Firstly,the samples in the deposited state were treated by different high temperature tempering methods to study the evolution process of Al-Si eutectic and further analyze the mechanical properties.Finally,nano-SiC ceramic particles with different contents were added to study the influence of nano-SiC particle content on the grain morphology and size of the material,and the mechanical properties were further analyzed.The results are as follows:(1)Under the two scanning strategies,columnar grains and equiaxed grains exist in the deposited samples of SLM AlSi10 Mg alloy.Among them,columnar crystals dominate the Molten Pool,and fine equiaxed crystals are mainly distributed along the Molten Pool Boundaries(MPBS).According to the non-uniform tissue characteristics of MPBS,MPBS was divided into four regions.In addition,there are MP coarse crystal area,Equiaxed crystal area and MP fine crystal area in the molten pool,and Heat Affected Zone(HAZ)around the molten pool.The heterogeneous microstructure in MPBS is closely related to the presence of Al/Si particles,the subcooling of composition and the pool conditions(temperature gradient G and growth rate of solid/liquid interface R).Al/Si particles exist in the partially pasty region and act as the core of heterogeneous nucleation during solidification.Compared with 90° layer rotation scanning strategy,67° layer rotation scanning strategy has stronger isotropic orientation distribution.The tensile strength and elongation of zigzag-90 in the horizontal direction are 494 MPa and 6.5%,respectively,and in the vertical direction are 467 MPa and 6.2%.The tensile strength and elongation of zigzag-67 are 455 MPa and 8.1% in the horizontal direction,and 474 MPa and 6.5%in the vertical direction.Under the same forming strategy,the horizontal direction shows a greater elongation.Fracture analysis results show that the cracks are mainly initiated at pores,MPBS,inclusions,Si particles and Al/Si interface.(2)After tempering at 400 ℃,450 ℃,500 ℃ and 550 ℃ for 120 min,the Si particles spheroidized and grew up in the tempered samples,and distributed uniformly in the matrix.The average size of Si particles increases from 0.25 μm to 1.65 μm when the tempering temperature increases from 400 ℃ to 550 ℃.The tensile strength of tempered AlSi10 Mg alloy is 213 MPa,209 MPa,119 MPa and 280 MPa from 400 ℃ to 550 ℃,but the ductility is obviously increased.15.0%,14.7%,17.7% and 11.7%,respectively.(3)When 0.8wt.%-1.6wt.% nano-SiC particles were added to enhance AlSi10 Mg alloy,the results of process optimization experiment show that the maximum density of the composite can reach 98.8% when the laser power is 180 W,the scanning speed is 900 mm/s,the scanning spacing is 130 μm,and the layer thickness is 30 μm.The effects of 0.8 wt.% and 1.2 wt.%nano-SiC particles on the grain size of composites are 8.9 μm and 8.5 μm,respectively,and the morphology of grains does not change.The addition of 1.6wt.% nano-SiC particles makes the grain morphology of SLM AlSi10 Mg alloy change from columnar grain to equiaxed grain,and the grain size is 2.8 μm,which decreases by 69.6% compared with the material without nano-SiC particles.The results of mechanical properties test show that the yield strength of SLM AlSi10 Mg alloy increases with the increase of nano-SiC particles,and the yield strength of0.8wt.%-1.6wt.% nano-SiC composite is 280 MPa,281 MPa and 292 MPa,respectively.The elongation is 6.0%,4.1% and 2.2%,respectively,and the contribution of fine grain strengthening to the yield strength is dominant.