Research On Ti-6Al-4V Shaped Metal Deposition By TIG Welding With Wire

Titanium alloy Ti-6Al-4V has been widely used in aviation and aerospaceindustry due to its high specific strength, excellent high temperature performance andcorrosion resistance. Traditionally, titanium components are manufactured bymachining on cast or forged pieces. The processing of complex components needs tocut more than90percents of raw material. The traditional component manufacturingmethods characterize high cost and low efficiency, because titanium is very expensive.Shaped metal deposition is an advanced technique to produce near-net shape and densecomponents in layerwise fashion. The advantages of this technique is apparent. On onehand, the manufacturing process need no mold and less time. On the other hand, theprocess only needs little following machining. Tungsten-Inert-Gas welding featureslow cost, no spatter and excellent shaping, so this thesis carried out researches onshaped metal deposition for manufacturing of titanium alloy Ti-6Al-4V components inorder to master the influence law of welding process on bead size, microstructure andmechanical properties. Currently, there is no research on this technique publiclyreported domesticly.This thesis researched the influence of process on bead size in single layerwelding, obtaining influence laws of welding parameters on weld width, weld height,width and depth of heat affected zone. The influence laws of welding parameters onbead size are described by trend charts. The influence degree of welding parameters onbead size are described by range analysis to reach the conclusion that welding currentimpacts weld width most and wire feeding speed impacts weld height most.Meanwhile, Multivariate linear regression equations between weld width, weld heightand process are established.Single wall components were manufactured using different welding parameters.The macro mophology and microstructure of the components were studied. Thecross-section of the SMD components is divided into top region, middle and bottomparts according to its microstructure characteristics. The top region of the componentmanufactured by shaped metal deposition consists of α′, αm, little basket-weavestructure and β phase. The middle and bottom parts of the component consist ofbasket-weave structure, colonies, α lamellae, little α′and β phase. Besides, there areband structure and convex bands on the cross-section. The thermal process of SMD isinvestigated, and analyzed by finite element modeling. The influence of weldingprocess on microstructure was studied by control variate method, obtained influencelaw of welding current, welding speed, wire feeding speed and interval time betweenlayers on microstructure. Mechanical properties of components by different welding parameters were tested.Anisotropy of mechanical properties of SMD components was discovered. All theproperties of the components produced by selected parameters satisfy the standard.When welding current, welding speed, wire feeding speed and interval time are120A,0.25m/min,1.6m/min and3min respectively, the tensile strength and elongation in Xdirection can reach947MPa and8.44percents, while, the tensile strength andelongation in Z direction can reach926.8MPa and11.5percents. The influence ofprocess on SMD components was investigated. The fracture and surface of the tensilesample were observed and analyzed, discovering that fracture mode belongs to ductilefracture.