The Influence Of Plastic Flow On The Weld Formation Of Linear Friction Welding For Titanium Alloy

In this paper, the plastic metal flow behavior and the effect of plastic metal flowon welding appearance of linear friction welding for annealed TC4titanium alloywere studied. The effects of welding parameters on welding appearance wereresearched by observing the morphology of weld cross sections. The plastic materialflow behaviors were researched on the weld cross sections, longitudinal sections byobserving the distribution of tracing material. The plastic metal flow model wasestablished and the effect of plastic metal flow on welding appearance was discussed.The results showed that matching of friction pressure, amplitude and frequencycaused the welds like the shape of “X”,“I” and “V”. The rate of heat productionbecamed slower and the extrusion of plastic metal reduced when the friction pressurewas low and the frequency and amplitude were constant, which caused the welds likethe shape of “X”. With the friction pressure increased, the interface heat productionrate increased, the extrusion of plastic metal also increased, the welds like the shapeof " I ". The weld heat input was low and heat loss also low when the frequency,amplitude were small and the friction pressure was constant, with the frequency,amplitude increased, the interface heat input increased, but the heat loss was high. Itcould easy be obtain the welds like the shape of “V” which contain defects.The distribution of tracing material on the cross-sections of welds suggested thatthe friction time and forging pressure had an effect on plastic metal flow, therebyaffecting the shape of the plastic layer. When the friction time was short, the plasticmetal flow along the axial direction and it caused the plastic layer change into“Spindle” type. With the increase of friction time, the width of the plastic layerincreased and the plastic metal migration to both sides of the weld and the plasticlayer change into “I” type. When the dwell time was short, the distribution of forgingpressure in the weld was large in the middle and small on both sides, which pressedthe plastic metal of weld flow from the middle to the side, the shape of weld was “X”.Extend the dwell time, the forging pressure force the plastic metal of side and theshape of weld was “I”.Based on the distribution of tracing material on the longitudinal-sections ofwelds, the formation and extension of plastic zone in the joint, the plastic metal flowbehavior and the deformation distribution of joint surface were obtained:(1) The plastic zone will spread rapidly into the bulk of the work-piece material, at theequilibrium stage of welding, the plastic zone almost keep a constant thickness;(2)The joint interface plastic metal on both side of parabola area will flow along theoscillation direction, the parabola region accounted for the cross-sectional area ofabout2/5, the plastic metal of remaining3/5joint interface area will flow along thethickness direction;(3) the area of severe deformed weld metal located on both sidesof vibration centerline within5mm, the deformation of weld metal gradually reducedform the center to the side, and the least deformed region appeared at the corner of thelongitudinal–sections.The analysis of plastic flow indicated that the plastic layer was constituted ofthermoplastic metal near the joint interface and part deformation layer metal farawayfrom the joint interface. In the both sides of the joint interface, the thermoplastic metalflowed along the oscillation direction, the thermoplastic metal in the center of jointinterface flowed along the thickness direction. The axial pressure forced the partdeformation layer metal flowed to the joint interface when the thermoplastic plasticmetal was extruded out of the joint interface.