Effect Of Scanning Strategy On Cracking Behavior Of QSi3-1 Copper Alloy Fabricated By Wire Arc Additive Manufacture

QSi3-1 copper alloy is widely used in aerospace,national defense and military industry,rail transit and other fields because of its excellent use,process and mechanical properties.Compared with the traditional manufacturing technology,the advantages of WAAM technology for forming QSi3-1 copper alloy parts are no need of die,short manufacturing cycle and high forming efficiency.Compared with the mainstream metal additive manufacturing technology with laser as heat source,the main advantages of WAAM technology are not only high forming efficiency and large forming size,but also can solve the problem of metal laser heating because the heat source of WAAM technology is arc It is difficult to form copper alloy because of its high reflectivity to laser.When using WAAM technology to form QSi3-1 copper alloy parts,crack defects often become a prominent problem restricting the application of this technology.Arc scanning strategies,such as scanning mode,scanning length and deposition height,are the key factors affecting the quality of the parts,which can greatly affect the cracking behavior of the parts.In view of this,this paper takes the QSi3-1 copper alloy revolving body as the research object,explores the influence of the scanning length and deposition height of revolving body on the cracking behavior of revolving body parts,and determines the best scanning length and deposition height.Based on the heat transfer theory of short segment multi-layer arc welding,the optimal range of scanning length and deposition height of QSi3-1 copper alloy revolving body formed by WAAM was determined.In this range,nine groups of experiments with different scanning length and deposition height were designed.The distribution characteristics of cracks on the surface of QSi3-1 copper alloy revolving body formed by WAAM and the cross-section and longitudinal section at different heights were studied by means of penetrant nondestructive testing.The effects of scanning length and deposition height on the crack formation were analyzed.The results of penetrant testing show that the suitable scanning length l is 150～200 mm,and the suitable deposition height h is 40～80 mm.On this basis,firstly,with the help of scanning electron microscope(SEM)and its attached energy dispersive spectrometer(EDS),the crack characteristics such as the number and total length of the cross-section cracks of the revolving body under different scanning lengths are observed and analyzed,and the influence law of the scanning length on the crosssection cracks of the revolving body is studied,and the optimal scanning length is determined as 200 mm.Then,the crack characteristics of different deposition heights of the section of the revolving body are observed and analyzed,and the influence of deposition height on the section crack of the revolving body is studied,and the optimal deposition height is 40 mm.In order to further analyze the formation mechanism of cracks in WAAM revolving body,the micro characteristics such as the direction and distribution of cracks at different positions of WAAM revolving body under different scanning length and deposition height were observed by OM and SEM,and the phase qualitative analysis of revolving body section was carried out by XRD.The results show that the formation of cracks is related to the characteristics of WAAM thermal cycle.Different cooling rates at different deposition heights will lead to large differences in grain size.The tensile deformation caused by uneven shrinkage during cooling exceeds the critical value.In addition,the segregation of Mn element in the alloy will lead to cracks along grain boundaries.The results show that both lattice distortion and grain preferred orientation growth can increase the number of cracks,and the selection of appropriate scanning length and deposition height can improve the preferential growth of grains,reduce the difference of grain size and reduce the number of cracks.Finally,combined with the thermal cycle characteristics of WAAM forming process,based on the heat transfer theory,the heat transfer process of the molten pool at different deposition heights of the revolving body is calculated theoretically,and the more accurate deposition height h is determined to be 58.4 mm.