MAIN TOPICS,ABSTRACTS &KEY WORDS

Research progress and prospect of numerical simulation of deposit morphology control in solid-state cold spray additive manufacturingLI Wenya1,2,XING Cihao1,2(1.State Key Laboratory of Solidification Processing,Northwestern Polytechnical University,Xi'an,710072,China；2.Shaanxi Key Laboratory of Friction Welding Technologies,Northwestern Polytechnical University,Xi'an,710072,China).pp 1-11

Abstract:Solid-state cold spray additive manufacturing(CSAM) technology has become increasing hot in research among many countries for its high deposition efficiency,fast deposition speed and low thermal effect.Since the deposition method of CSAM is quite different with that of the traditionally laser additive manufacturing,the control of the deposit morphology has become a major task in the application of the technology.Based on the current conditions,numerical simulation methods have been carried out to study the effect of cold spray on the morphology of deposition.The results show that numercial simulation is a good way to predict and control the deposit morphology.In this paper,various simulation methods were proposed to predict the depositon morphology of CSAM and the characteristic of each method were summarized.Finally,challenges at present and prospect of the simulation of CSAM deposit morphology were proposed.

Highlights:Numerical simulation is becoming the main methodology for predicting deposit morphology for cold spray additive manufacturing,which provides theoretical guidance for morphology control of CSAM deposits and spraying path planning.

Key words:solid-state additive manufacturing；cold spray；morphology control；numerical simulation

Influence of layer thickness on the microstructure and mechanical properties of selective laser melting processed GH3625ZHU Jie1,ZHOU Qingjun2,CHEN Xiaohui1,FENG Kai1,LI Zhuguo1(1.Shanghai Key Laboratory of Materials Laser Processing and Modification,Shanghai Jiao Tong University,Shanghai,200240,China；2.Capital Aerospace Machinery Co.,Ltd.,Beijing,100076,China).pp 12-17

Abstract:To investigate the influence of layer thickness on the microstructure and mechanical properties of laser powder bed fusion processed GH3625,specimens were prepared with different layer thickness while other parameters remained unchanged before they were studied in aspect of microstructure and tensile properties.It is shown that the density of specimens has not been influenced by layer thickness under a wide range of processing parameters.Besides,with optimized processing parameters,specimens with a density over 99.9% can be fabricated by 0.02 mm and 0.03 mm layer thickness at the same time.The increase of the layer thickness will lead to the change of molten pool morphology,and also significantly change the grain morphology.When the thickness of powder bed was 0.02 mm,the average grain size was about 18.128 μm,and the grain had obvious preferential orientation.At this time,the adjacent molten pools differ greatly in shape,showed the phenomenon that one secondary was deeper and wider,and the other secondary was shallow and narrow.When the layer thickness increased to 0.03 mm,the temperature gradient difference decreased,the morphology difference of adjacent molten pools was small,the elongated grains in the microstructure decreased,the average grain size decreased to 11.921 μm,and the preferred orientation of grains also weakened.Due to changes in grain structure and grain size,the yield strength was increased by about 5% in the 0.03 mm specimen than that of the 0.02 mm specimen in vertical direction,contributing to less anisotropy in mechanical property.

Highlights:(1) Under an optimized process,although with the same pramaters,high density specimens can still be obtained with larger layer thickness.

(2) The increase in layer thickness weakens the texture in the microstructure and therefore restrains the anisotropic features.

Key words:selective laser melting；layer thickness；microstructure；tensile properties

Effect of heat treatment on the microstructure and mechanical properties of wire arc additively manufactured ferrite/martensitic steel for nuclear applicationsZHOU Yaju1,YIN Shengming1,XIA Yongzhong1,YI Guoqiang1,XUE Lihong1,YAN Youwei1,2(1.State Key Laboratory of Materials Processing and Die &Mould Technology,Huazhong University of Science and Technology,Wuhan,430074,China；2.Huazhong University of Science and Technology,Wuhan,430074,China).pp 18-26

Abstract:Reduced activation ferritic/martensitic (RAFM)steel was fabricated by wire and arc additive manufacturing(WAAM) technology.The microstructural evolution was observed by optical microscope,scanning electron microscope and transmission electron microscope and the mechanical properties were tested by a tensile tester to study the effect of heat treatment on the microstructure and mechanical properties of WAAM RAFM steel.The results showed that the microstructure of as-built RAFM steel consisted of dual phases of ferrite and tempered martensite and the average grain size was about 1.51 μm.After heat treatment,the RAFM steel showed no significant increase in grain size (1.84 μm),and high-density dislocations were retained in the microstructure.In addition,a large number of TiO2secondary phase nanoparticles,with the grain size of 5-10 nm,have precipitated and dispersed in the matrix after the heat treatment.The tensile strength of WAAM RAFM steel was significantly improved after heat treatment while the elongation after fracture was slightly reduced.The tensile strength of RAFM steel after heat treatment was 1 080 MPa at room temperature and even at a temperature of 650 ℃,it can still reach about 285 MPa.

Highlights:(1) The effect of heat treatment on the microstructure of WAAM RAFM steel was systematically studied in terms of phase structure,grain size and secondary phase precipitations.

(2) The strengthening mechanism of WAAM RAFM steel after heat treatment was elucidated.

Key words:wire and arc additive manufacturing；reduced activation ferritic/martensitic steel；heat treatment；microstructure

Interfacial characterization and properties of Ti6Al4V/NiTi laser additive manufactured functional gradient materialsLI Xingran,LIU Zhenglin,JIANG Pengfei,NIE Minghao,ZHANG Zhihui(Key Lab of Bionic Engineering Ministry of Education,Jilin University,Changchun,130000,China).pp 27-33

Abstract:Ti6Al4V/NiTi bionic function graded materials(BFGM) with dense and defect-free microstucture were prepared by laser additive manufacturing technology,and their interfacial microstructure,precipitation phase characteristics and mechanical properties were investigated.The results show that the Ti6Al4V/NiTi BFGM exhibits a non-uniform microstructure consisting of various grain morphologies and irregular and abnormal eutectic tissues,which are mainly titanium-rich and nickel-rich solid solutions and (Ti,Ni) compounds.As the content of NiTi alloy increases,the number and morphology of precipitated phases in different deposition layers change significantly.The microstructure of BFGM undergoes a series of transformations: α+β biphasic microstructure → columnar crystals+irregular eutectic structure → columnar crystals →equiaxial crystals → equiaxial crystals+columnar crystals.Phase aggregation,separation and segregation during solidification have significantly affected the mechanical properties of BFGM.The maximum microhardness of BFGM is 730.9 HV,which is attributed to the presence of brittle Ti2Ni phase.The tensile strength is 202 MPa and the elongation is 6.5%,which is significantly higher than that of the directly connected Ti6Al4V/NiTi heterogeneous material.The tensile fracture is characterized by brittle fracture with multiple secondary cracks extending along the crystal.

Highlights:(1) The defect-free Ti6Al4V/NiTi bionic functional gradient material is manufactured by laser additive manufacturing technology,and the defect-free interfacial microstructure and excellent mechanical properties were obtained.

(2) The microstructure evolution of different deposited layers of bionic functional gradient materials is revealed.

Key words:laser additive manufacturing；functional gradient materials；heterogeneous metallic materials；interface mircrostructure；mechanical properties

Path optimization for wire arc additive manufacturing based on adaptive contour skeleton zoning methodZHAO Tao,YAN Zhaoyang,JIANG Fan,XIAO Jun,CHEN Shujun(Faculty of Materials and Manufacturing,Beijing University of Technology,Beijing,100124,China).pp 34-40,63

Abstract:The traditional contour offset path planning strategy for arc-based directed energy deposition of mediumsized complex parts has a high degree of geometric fidelity.However,continuous offsetting of original contour can easily lead to underfilled regions and defects,that can be forming the area to be optimized.To address this,a precise defect identification method based on Boolean operations is proposed.The defect region is obtained by calculating the Boolean difference between the original and backtracked polygons.This region is reconstructed into skeleton-filled areas through filtering and merging.The optimal filling direction of skeleton-filled areas is determined by the minimum rectangular box,and the zigzag path is generated.Finally,the contour offset path is reclassified and connected to form a continuous forming path.The forming path of skeleton-filled areas is firstly transformed into machine code.In the subsequent forming test,the propeller parts were printed by the robot arc additive manufacturing system.The results indicate that the parts have achieved the expected forming size,and there are no defects in the traditional method.This proves that the method has highly feasible and applicable.

Highlights:(1) A skeleton filling method is proposed to accurately identify and filter defect areas in the traditional contour offsetting method.

(2) The optimized contour offset path retains the advantages of the traditional method while reducing the number of arc starts and stops.

Key words:wire arc additive manufacturing；contour offset；Boolean operation；defect recognition；hybrid path planning

Microstructure and corrosion resistance analysis of aluminum/steel "arc+friction stir" hybrid additive manufacturingMIAO Yugang1,LIU Ji1,ZHAO Yuyang1,LI Chunwang1,WANG Ziran1,ZHANG Benshun2(1.Harbin Engineering University,Harbin,150001,China；2.Jiangsu Automation Research Institute,Lianyungang,222006,China).pp 41-48

Abstract:In order to realize the manufacturing of aluminumsteel composite structures,this study proposed a new method of"arc+friction stir" hybrid additive manufacturing.First,BCMIG welding is applied to deposit a thin transition layer of aluminum alloy on the surface of galvanized Q235 steel,and after which the transition layer and the the 6061 aluminum alloy is produced by friction stir additive manufacturing.During the arc deposition of the transition layer,the galvanized layer and the bypass arc have promoted the wetting and spreading of droplets on the steel surface,thus help to form a flat surface.The subsequent friction stir additive manufacturing process eliminated porosity and cracks in the transition layer and brought about a well-formed and defect-free aluminumsteel composite structure.The effects of different wire compositions (Al-Si and Al-Mg) on the microstructure and corrosion resistance of Al-steel composite structures were investigated.The results showed that the wire composition,instead of affecting the weld formation,will affect the thickness of the Fe-Al intermetallic compounds layer at the interface.Besides,the corrosion resistance of Al-steel structures filled with Al-Si wire is better than that with Al-Mg wire,as galvanic corroion will occur among the intermetallic compounds at the interface,while the substrate is tend to be corroded first,so that the corrosion resistance of the Al-steel composite structure is decreased.

Highlights:(1) A novel approach for hybrid additive manufacturing of dissimilar aluminum/steel alloys,termed "arc +friction stir",is introduced,which effectively resolved issues related to the wear and tear of the stirring pin caused by direct contact with steel.Additionally,it successfully eliminated defects such as porosity and cracks generated in the transition layer during arc cladding through the subsequent friction stir additive process.

(2) When compared to Al-Mg welding wire,employing Al-Si welding wire as the transition layer filler material demonstrated the potential to reduce the formation of intermetallic compounds,thereby effectively inhibiting galvanic corrosion within the assembly.

Key words:aluminum/steel heterogeneous metal；bypass current；friction stir additive manufacturing；intermetallic compounds；corrosion resistance properties

Influence mechanism and improvement strategy of aspect ratio on the poor fusion between laser cladding channelsYANG Gaolin1,2,ZHENG Quanhang1,2,QIAN Haokai1,2,FAN Wen1,2,ZHANG Qunli1,2,SHI Yuelin3,YAO Jianhua1,2(1.Institute of Laser Advanced Manufacturing,Zhejiang University of Technology,Hangzhou,310023,China；2.Collaborative Innovation Center of High-End Laser Manufacturing Equipment,Hangzhou,310023,China；3.Zhoushan Dingzun Intelligent Technology Co.,Ltd.,Zhoushan,316031,China).pp 49-56

Abstract:Poor fusion is a common process defect in laser cladding.In order to explore the mechanism of poor fusion during inter-track overlap,single-track single-layer cladding test,multi-track single-layer cladding test,multi-track remelting test and single-layer tail-track remelting test were designed,and the simulation of temperature field during single-track cladding was carried out.The results show that the formation mechanism of the poor fusion defect is that the upper part on edge of the deposited area is raised,and the heat dissipation is slower and the melting is faster when the laser irradiates its surface.The laser energy input at the edge root is low and the shape is concave.so the heat dissipation is fast and the melting is slow.The molten liquid is turned out by the upper convex part and connected with the molten part of the root and the substrate,resulting in the gap between the root of the cladding layer and the laser,resulting in poor fusion defects.In order to reduce the occurrence of such poor fusion defects,a single-layer multi-pass lap test of the inclined cladding head was designed according to the mechanism of poor fusion.The results show that the inclined cladding head can effectively reduce the occurrence of poor fusion defects.

Highlights:(1) The mechanism of poor fusion defects generated by laser cladding was studied.

(2) A method is proposed to reduce the occurrence of poor fusion defects by changing the angle of the cladding head.

Key words:poor fusion；width-height ratio；laser cladding；additive manufacturing

Microstructure and properties of titanium alloy made by plasma arc and AC auxiliary arc additive manufacturingSHEN Lei1,HUANG Jiankang1,2,LIU Guangyin1,YU Shurong1,FAN Ding1,2,SONG Min3(1.Lanzhou University of Technology,Lanzhou,730050,China；2.State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metal,Lanzhou University of Technology,Lanzhou,730050,China；3.Dalian Shipbuilding Industry Company,Dalian,116103,China).pp 57-63

Abstract:Using plasma arc as heat source,the additive manufacturing of titanium alloy fuses layer by layer was carried out by AC assisted method.The influence of AC value on the microstructure and properties of the additive specimen was studied.The influence of the auxiliary AC value on the droplet size and droplet transition was observed by high-speed photography,the roughness of the stack morphology was measured,the structure and microhardness of the stack were observed,and the influence of the auxiliary AC value on the compression performance of the stack was analyzed.The results show that a more obvious AC arc will be formed and the plasma arc will swing,which will oscillate the molten pool.The surface roughness and grain size of the additive specimen are improved,and the grain size decreases with the increase of the applied auxiliary AC.When no AC is added to the AC value of 30 A,the grain size is reduced by 43.4%.At the same time,the addition of auxiliary AC can significantly improve the hardness and plasticity of the additive specimen.When the external auxiliary AC is 30 A,the hardness is 454.15 HV,and the compression strain is 0.280%.Without AC,the hardness is 406.45 HV and the compressive strain is 0.110%,which is increased by 2.5 times.

Highlights:The effect of AC aid on the arc shape and the grain size,microstructure and properties of the arc additive specimen in the process of arc additive manufacturing titanium alloy was studied.

Key words:AC assisted；wire arc additive manufacturing；microstructure；mechanical properties

Microstructure and mechanical properties of Al-Mg-Cu alloy fabricated by heterogeneous twin-wire indirect arc additive manufacturingWU Tao1,TAN Zhen1,WANG Liwei1,2,LIANG Zhimin1,2,WANG Dianlong1,2(1.Hebei University of Science and Technology,Shijiazhuang,050018,China；2.Hebei Key Laboratory of Material Near-Net Forming Technology,Shijiazhuang,050018,China).pp 64-70

Abstract:A new heterogeneous twin-wire indirect arc additive manufacturing (TWIA-AM) method was proposed.The ER2319 wire and ER5356 wire were fed synchronously and Al-3.5Mg-1.7Cu alloy components were prepared.The microstructure and mechanical properties of the deposited Al-3.5Mg-1.7Cu alloy components were investigated.The results showed that the second phase composition of Al-3.5Mg-1.7Cu alloy was mainly Al,Mg and Cu,and consisted of α-Al and S (Al2CuMg) phases.The grain morphology appeared as coarse columnar crystals at interlayer regions,and the center area of the layer is composed of equiaxed crystals and fine cellular crystals,and the layer center region was composed of equiaxed crystals and fine cellular crystals.The average microhardness of the sample is 73.7 HV with a periodic low hardness zone.The average tensile strength and elongation of the samples parallel to the building direction (BD direction) and perpendicular to the BD direction were 225,235 MPa,9.0%and 13.0%,respectively,exhibiting anisotropic mechanical properties.The fracture morphology exhibited the characteristics of typical plastic fracture.

Highlights:A new heterogeneous twin-wire indirect arc additive manufacturing method is proposed,and additive manufacturing of Al-Mg-Cu alloy is achieved by in-situ synthesis.

Key words:twin-wire indirect arc；additive manufacturing；Al-Mg-Cu alloy；microstructure；mechanical properties

Comparative study between powder feeding and wire feeding laser additive repairing of V-groove with Inconel 718 alloyYAO Zhehe1,2,QIAN Hongyu1,2,YU Peijiong3,CHEN Yalun1,2,ZHANG Qunli1,2,LIU Yunfeng1,YAO Jianhua1,2(1.Zhejiang University of Technology,Hangzhou,310023,China；2.Collaborative Innovation Center of High-End Laser Manufacturing Equipment,Hangzhou,310023,China；3.Hangzhou Steam Turbine Co.,Ltd.,Hangzhou,310020,China).pp 71-78

Abstract:Laser cladding technology has been widely used in additive repairing of key components,and powder feeding and wire feeding are the main methods used during this process.In this study,laser additive repairing of V-groove with Inconel 718 powder and wire were conducted to study how they would affect the repairing quality of the superalloy .Numerical simulation and experiments were carried out to compare the effects of powder and wire feeding methods on the V-groove temperature field,molten pool profile,macroscopic morphology and microstructure of the repaired zone during laser repairing.The results indicate that powder and wire feeding methods affect the absorption of laser energy by V-grooves and molten pools.During the powder feeding repairing,the temperature is higher at the bottom of the V-groove,resulting in a 45.5% increase in the melt depth of the repair zone.Powders in state of solid and semisolid were sprayed onto the molten pool,resulting in a coarser surface in the repairing zone.In addition,the grain size in the repaired zone grows gradually as the depth decreases,and the difference in grain orientation in the center of the repaired zone is also significant.

Highlights:(1) Laser energy absorption and transfer mechanism in the molten pool were revealed during laser additive repairing of V-groove with powder feeding and wire feeding methods.

(2) The microstructure of the repaired zone and the heat flow evolution during the solidification of the molten pool were analyzed both with powder feeding and wire feeding methods.

Key words:powder feeding method；wire feeding method；laser additive repairing；V-groove；temperature field

Finite element analysis of the effect of ultrasonic impact on the stress of aluminum alloy arc additive manufacturingLIANG Hui1,LI Pan1,SHEN Xin2,CHEN Lifan1,DAI Junhui1,LI Dong3,YANG Dongqing1,3(1.Key Laboratory of Controlled Arc Intelligent Additive Technology,Ministry of Industry and Information Technology,Nanjing University of Science and Technology,Nanjing,210094,China；2.China North Industries Group,Jinxi Industrial Group Co.,Ltd.,Taiyuan,030000,China；3.Guangdong Key Laboratory of Advanced Welding Technology for Ships,CSSC Huangpu Wenchong Shipping Co.,Ltd.,Guangzhou,510715,China).pp 79-85,119

Abstract:The finite element analysis was used to numerically simulate the process of arc additive manufacturing of 2219 aluminum alloy under ultrasonic impact,and the changes in stress fields and component deformation were studied.The results show that the additional ultrasonic impact can reduce the stress concentration at the edge of the sediment and at the area close to the sediment in the substrate during the multi-layer multi-channel deposition.Additional ultrasonic impact during multi-layer multi-channel deposition can effectively reduce the stress inside the sediment.After the ultrasonic impact,the stress range at the interface between layers decreased from 156.1-211.6 MPa to 138.8-181.9 MPa,and the average residual stress on the surface decreased by 22.3%.Under the ultrasonic impact,the maximum deformation of multi-layer multi-pass arc additive component decreased from 0.61 mm to 0.53 mm,and the average deformation decreased from 0.33 mm to 0.27 mm.The stress distribution on the upper surface of the multi-layer sediment calculated by the finite element is similar to that of the measured in actual experiment,which proves that the simulation results are reliable.

Highlights:(1) A finite element model for multi-layer multipass arc additive manufacturing is established,and the ultrasonic impact load is reasonably simplified.

(2) The application of ultrasonic impact can significantly reduce the residual stress and deformation of arc additive manufactured components.

Key words:ultrasonic shock；2219 aluminum alloy；wire arc additive manufacturing；finite element analysis

Microstructure and properties of 316L stainless steel fabricated by speed arc wire arc additive manufacturingWANG Qiang1,WANG Leilei1,2,GAO Zhuanni1,YANG Xingyun1,ZHAN Xiaohong1(1.Nanjing University of Aeronautics and Astronautics,Nanjing,211106,China；2.Shenzhen Research Institute,Nanjing University of Aeronautics and Astronautics,Shenzhen,518000,China).pp 86-93

Abstract:The 316L stainless steel component was manufactured by speed arc wire arc additive manufacturing(WAAM)under constant current.The formation of the component was explored,and the microstructure and mechanical properties at different regions of the component was compared under the scanning electron microscopes and the metallurgical microscope.The results indicate that the primary dendrites(PD)transform from acicular dendrites,strip dendrites to columnar dendrites along the deposition direction in single layer.The dimensions of secondary dendrites(SD) increases with the deposition height.The secondary dendrite arms sizes(SDAS) are 11.54,12.50 μm and 15.52 μm at the bottom,middle and top of the sample,which are mainly affected by heat accumulation.In addition,the tensile strength of the sample along the deposition direction and scanning direction is 517 MPa and 527 MPa,exceeding the strength of forging.The percentage elongation after fracture of the sample is 22.5% and 15.0%.And the fracture mode of tensile samples is ductile fracture.However,the plasticity and the ductility of samples adopted along the scanning direction is better than that of the samples in the deposition direction.

Highlights:The 316L stainless steel component was fabricated by speed arc mode,the influence of dendrite morphology and heat accumulation in the single layer on the size changes of the secondary dendrite arms in the upper,middle and bottom of the sample was discussed,and the tensile properties of the deposited samples in different directions were analyzed.

Key words:the speed arc mode；316L stainless steel；morphology of dendrites；mechanical property

Effect of heat input on microstructure and mechanical properties of wire arc additive manufactured super duplex stainless steelLI Ke1,2,NIU Ben1,PAN Linlin1,YI Jianglong1,ZOU Xiaodong1(1.Key Laboratory of Modern Welding Technology of Guangdong Province,China-Ukraine Institute of Welding,Guangdong Academy of Sciences,Guangzhou,510651,China；2.Department of Intelligent Manufacturing,Wuyi University,Jiangmen,529030,China).pp 94-101

Abstract:In order to investigate the influence of heat input on the microstructure and properties of wire arc additive manufactured super duplex stainless steel,sample tests were conducted by MIG arc additive manufacturing of a sing-wall on a substrate of Q345 low carbon alloy steel,using ER2594 super duplex stainless steel wire 1.2 mm in diameter with different heat inputs applied.The microstructure and mechanical properties of each sample were analyzed.The results showed that when the heat input was increased from 435.6 J/mm to 517.3 J/mm,the austenite content grew from 31% to 43%,which was attributed to the greater heat input and the slower cooling rate.When the heat input was further increased to 599.0 J/mm,the austenite content decreased from 43% to 41% due to the loss of nitrogen content.With continuous increase of heat input (from 435.6 J/mm to 599.0 J/mm),the microhardness was initially decreased and then increased,since microhardness is positively correlated with ferrite content.The sample with a intermediate heat input value (517.3 J/mm) exhibited better tensile performance due to its high austenite content.

Highlights:(1) Three groups of super duplex stainless steel walls with different heat inputs were fabricated using the wire arc additive manufacturing.

(2) This study elucidated the mechanism that high heat input will result in nitrogen element burn-off and decrease the austenite content in the microstructure.

(3) The study revealed that a balanced ratio of ferrite and austenite contributes to improve tensile performance,whereas increased residual stress diminishes the tensile property.

Key words:super duplex stainless steel；heat input；wire arc additive manufacturing；nitrogen element；austenite content

Comparative study on the microstructure and mechanical properties of the laser welded joints of additive manufactured and forged TC11 titanium alloyWANG Meng,ZHANG Liping,ZHAO Linyu,WU Jun,XIONG Ran,MENG Yongsheng,LI Junhong(Xi'an Aerospace Power Machinery Co.,Ltd.,Xi'an,710038,China).pp 102-110

Abstract:Additive manufacturing of large-size components for aerospace applications is always limited by processing efficiency and the maximum machining dimension of the equipment.Therefore,it is expected that a hybrid manufacturing technology combining additive manufacturing and welding will tackle this problem.In this paper,laser welding tests of additive and forged TC11 titanium alloy were carried out.The weldability of additive TC11 titanium alloy (TC11-AM),of"TC11-AM/forged TC11 (TC11-R)" joint and of TC11-R/TC11-R joint were studied.The microstructure of welded joints,hardness and tensile tests were conducted,and the fracture morphologies of tensile specimens were observed.The results show that no obvious porosity was found in the weld zone of TC11-R/TC11-R joint,TC11-AM/TC11-R joint,or TC11-AM/TC11-AM joint.Due to the large temperature gradient and fast cooling rate of the molten pool,the microstructure of the weld was coarse columnar grain with α'martensite phase inside.The tensile strengths of the three joints mentioned above were about 1 575,1 687 MPa and 1 593 MPa,respectively.The cross sectional microhardness of TC11-R/TC11-R and TC11-AM/TC11-AM joints shows Gaussian distribution,and the variation range ΔHV of hardness values was about 445 HV ± 31 HV and 424 HV ± 6 HV,respectively.Due to the notable difference in the microstructures at different zones of the joint,the microhardness of TC11-AM/TC11-R joint showed a ladder-shaped distribution with higher hardness in TC11-AM side and lower hardness in TC11-R side,and the range of hardness was about 432 HV ± 21 HV.By comparing the tensile strength of the joints,it is found that TC11-AM/TC11-R joint and TC11-AM/TC11-AM joint are better in terms of weldability.

Highlights:(1) The differences in microstructure and mechanical properties of TC11-AM/TC11-R,TC11-AM/TC11-AM and TC11-R/TC11-R joints were compared and analyzed.

(2) The influence of different base metal states on Vickers hardness distribution of welded joints was analyzed.

Key words:additive manufactured TC11 titanium alloy；forged TC11 titanium alloy；laser welding；microstructure；mechanical property

Comparison of ultrasonic transverse and longitudinal wave porosity detection in additive manufacturing of AlSi10MgZHANG Chenhao,CHEN Bing,LIU Heng,XIANG Pengyu,GOU Guoqing(Southwest Jiaotong University,Chengdu,610031,China).pp 111-119

Abstract:With more extensive and in-depth application of additive manufacturing in various fields,non-destructive inspection are in growing needs in additive products for its fast and high quality inspection.Porosity is an important factor determining the mechanical properties of the additive products,so it is very important to characterize it during the inspection process.In this paper,the laser power and scanning speed are adjusted to change the volume energy density,and the AlSi10Mg specimens with different porosities are obtained.The ultrasonic transverse and longitudinal waves were used to test the specimens,and the corresponding sound velocity and attenuation coefficient were obtained.The results show that the transverse and longitudinal sound speeds are inversely proportional to the porosity size,and the attenuation coefficients are directly proportional to the porosity size.When using sound velocity to characterize the porosity,the absolute value of longitudinal sound velocity is more variable,so the accuracy is better.Because the shear modulus of longitudinal sound velocity changes more than that of transverse sound velocity,the linearity is 22% higher than that of transverse sound velocity.When the attenuation coefficient is used to characterize the porosity,the accuracy of transverse wave is better than that of longitudinal wave because transverse wave of the same frequency is shorter in wavelength,and is more sensitive to the direction of polarization,so the linearity is 13% higher than that of the longitudinal wave.

Highlights:(1) The propagation mechanism of ultrasonic transverse wave and ultrasonic longitudinal wave in additive manufacturing of AlSi10Mg specimens is revealed.

(2) The different characteristics of ultrasonic transverse waves and ultrasonic longitudinal waves in porosity detection were analyzed.

Key words:ultrasonic transverse wave；ultrasonic longitudinal wave；additive manufacturing；porosity

Application of variable layer thickness slicing algorithm in wire arc additive manufacturingLIU Shuaiqi1,LIU Renpei1,LI Zhongmin2,DU Xinwei1,SHEN Yonghua1(1.Nanjing University of Aeronautics and Astronautics,Nanjing,210000,China；2.Tianrun Industrial Technology Co.,Ltd.,Weihai,264413,China).pp 120-126

Abstract:When applying wire arc additive manufacturing technology to repair damaged molds,poor forming problems such as gaps,dents and excessive accumulation may occur at the edges,which lead to the uneven thicknesses in the clading layer and impact the precision of the additive manufactured parts.In order to aovid these defects,a variable thickness layer slicing algorithm is proposed,which mainly consists of model pre-processing,determination of welding parameters,correction of slicing thickness,and completion of the additive manufacturing process.By adjusting the overlap rate during the cladding process,precise control of the thickness variation of the formed part can be achieved,which help to improve the forming precision and decrease the defects as mentioned above.Finally,this variable layer thickness slicing algorithm was used for pyramid structure models,and cladding experiments were conducted.The results showed that the calculated filling path could fully ensure the full filling of the specified layer,and there was little difference in height,length and width between the cladded part and the calculated one.Hence,the forming precision is satisfactory to the industrial requirements on condition that the heat accumulation is low.

Highlights:(1) Compared with the traditional equal-thickness slicing algorithm in arc additive manufacturing technology,the proposed algorithm can ensure that under the parameters of a specific welding process,the relative error between the calculated value and the actual value of layer thickness can be kept within a samll range.

(2) The application of the variable thickness slicing algorithm can effectively tackle the problems of dents and overstacking caused by unreasonable slicing of layers during the additive manufacturing process,and contributes to the high precison of the additive mold.

Key words:wire arc additive manufacturing；variable layer thickness slicing algorithm；forming defect；mold repair

Effect of the additional water-cooling on the microstructure and mechanical properties of wire arc additive manufacturing of 4047 aluminum alloyWU Kai,BU Zhixiang,KUANG Xiaocao,WEI Ligeng,WANG Lishi(Hubei University of Technology,Wuhan,430068,China).pp 127-132

Abstract:In order to solve the problem of deposited metal collapse caused by heat accumulation effect during the continuous process of wire arc additive manufacturing,a water-cooling aluminum plate was applied to the bottom of the substrate,and 4047 aluminum alloy straight wall components were prepared under two processes: intermittent forming with watercooling,and continuous forming with water-cooling.A component was also additived without water-cooling for benchmark specimen.By comparing the thermal cycle curve,grain morphology,tensile strength,hardness and elongation,the effect of water-cooling conditions on the macroscopic morphology,microstructure and mechanical properties of the additive components were analyzed.The results showed that heat accumulation was effctively reduced by water-cooling,and flatter component side walls were obtained.The straight wall additive component exhibited the best performance under the continuous forming with water-cooling,showing no collapses at either end,and the forming efficiency was also high.The grains at the bottom of the components are mainly equiaxed crystals,and columnar and dendritic crystals at other sites.The grain size of the component is the largest under continuous forming with water-cooling and the smallest under intermittent forming with water-cooling.The mechanical properties of all components are similiar to that of ZL102 casting aluminium alloy.The component prepared by the intermittent forming with water-cooling exhibited the best mechanical properties.

Highlights:(1) By applying water-cooling aluminum plate to promote heat dissipation,the problem of coating collapses during continuous arc addictive manufacturing of 4047 aluminum alloy was solved,and the forming quality of the additive component was improved.

(2) Continouous wire arc additive manufacturing under watercooling conditons has not only produced components with satisfactory performance but also improved the forming efficiency.

Key words:wire arc additive manufacturing；aluminum alloy；water-cooling condition；microstructure；mechanical properties