Study On The Additive Manufacturing Technology Of Directly Micro Fused-casting For Metal

High strength alloy parts with complex structure have been widely used in the field of aviation,aerospace and military industry.Among varieties of processing techniques,direct forming complex metal parts by additive manufacturing(AM)technique is an eye catching topic in the research world.Using metal powers or wires,products are manufactured by piling up with alloy melted by laser or ion beam.However,certain limitations,such as the properties of the metal powder or wire,could restrict the performance of the final product.In order to improve existing AM technique,this study developed a new kind of technology in the field of AM:directly micro fused-casting for metal(MFCM).High strength metallic product with complex structure could be directly prepared by metal melt through this technique.The manufacture equipment of low temperature alloy(Sn-Pb)was built in terms of basic principles of MFCM,and the manufacture parameters of MFCM on Sn-Pb alloy was fully explored,as well as the properties of final products.Furthermore,the manufacture equipment for high temperature alloy,ZL101,was built.The influence of manufacture parameters on the fomability of ZL101 alloy were studied.In addition,the microstructure of samples were analyzed,and the mechanical properties were tested.This study mainly includes:(1)According to the principle of MFCM and material properties of Sn-Pb alloy,the manufacture equipment for Sn-Pb alloy was built.The single-layer,multi-layer circular and hyperboloid Sn-Pb alloy samples with uniform structure were prepared.The 5 layers and 10 layers sample presented uniform micro hardness and strong interface between different layers,which were 11.21±0.65 HV and 11.36 ± 0.83 HV,respectively,higher than the raw material of Sn-Pb(9.76 HV).(2)In order to apply the micro fused cast into high-melting-point alloy,the equipment has been upgraded.Graphite crucible,force stirring and 6° inclined high-strength graphite piston rotary switch were adopted to control the flow of melting aluminum alloy.The nucleation and growing mechanism of semi solid ZL101 was explored,and the preparation process was then determinted.It shows that the fine grains with average grain size of 51 ?m was obtained with following parameters:the temperature of bucket and nozzle are 620 and 595?,respectively,and the stir speed of 800 r/min.Fine and near-global ?-Al grains evenly distributed in the final product,with high shape factor up to 0.7.(3)The effect of substrate moving speed and the height between substrate and nozzle on the microstructure and mechanical properties of sample were studied.Results show that the average grain size decreased with higher speed and lower height,while the properties of products became better.The tensile strength and microhardness of the best single-layer samples,which prepared at substrate speed of 20 mm/s and height of 2 mm,were 240.82 MPa and 83.57 HV,respectively,about 45%and 28%higher than the raw material.(4)Effect of substrate speed on the grain size and texture orientation of samples was studied by Electron Backscattered Diffraction(EBSD).Results show that the average grain size decreased and the texture orientation became more obviously with the increasing of substrate moving speed.The rapid movement of the substrate results in rapid cooling of the melt,further leading to the growth of grains along the direction of heat flow.When the substrate movement speed was 10 mm/s,20 mm/s and 30 mm/s,the average grain size was 73 ?m,59 ?m and 46?m,respectively.(5)The FLUENT software was applied to simulate the melting conditions between the micro fused interfaces.It is found that lower metal surface could be melt when the temperature reached 600-610 ? and the substrate moved between 5-20 mm/s(the depth of the melting layer is 22-155 ?m),leading to a strong interface.According to the results of simulation,the sample is produced with tightly bonded interface,and the tensile strength of samples was 208.35 MPa.The interlayer bonding mechanism of micro fused cast show that the layer of metal surface melts first,then the heating metal atoms diffuses in the interlayer,the metallurgical combination is formed finally between the cambium after solidification.