Microstructure Evolution And Mechanism Of Wire And Arc Additive Layer Manufacturing TC4 Components

Ti-6Al-4V titanium alloy is widely used in aviation,aerospace and other fields due to its high specific strength,good corrosion resistance and outstanding high temperature performance.However,the efficiency of titanium alloy in traditional manufacturing process is lower and the cost is higher,due to its lower thermal conductivity and higher chemical activity.Wire and Arc Additive Layer Manufacturing(WAALM)is a novel manufacturing technique in which metal components can be fabricated layer by layer and offers the potential to reduce cost and improve efficiency.Cold Metal Transfer(CMT)is a modified GMAW variant based on a controlled dip transfer mode mechanism.The process delivers excellent quality,lower thermal heat input,and nearly spatter free weld.Therefore,in this paper,a Cold Metal Transfer(CMT)method has been carried out to study the manufacturing process of TC4 Wire and Arc Additive Layer Manufacturing.In this paper,the mathematical model of wire feeding speed and welding speed and layer height,layer width,HAZ depth and HAZ width are established by the response surface analysis method.Through the analysis of variance analysis and model verification,it has proved that the established mathematical model can be used to predict the size of single channel and single layer material increase and optimize the process parameters.It has found that the influence of welding speed on the layer height,layer width,HAZ depth and HAZ width was the most significant negative correlation,followed by the positive correlation of wire feeding speed.The process parameters were optimized with lower layer height,wider layer width,shallow HAZ depth and lower consumption.The optimization results show that when the wire feeding speed was 6.4m/min and the welding speed was 0.25m/min,the best balance result can be obtained between the optimal forming,the best efficiency and the minimum cost.The characteristics of the macro and micstructure were also studied in this paper.During the process of WAALM,mainly two types of macrostructure were generated,one was the prior β grains boundary which grew perpendicularly from substrate almost crossing multiple deposition layers,and the other was the layer bands which were parallel to deposited layer.The microstructure was mainly composed of acicular α and the residualβ-phase,martensite α ’,prio-β grain boundaries,basketwave structure,widmanstatten structure,massive α-phase structure etc.It was also found that the micstructure of thin-walled components of TC4 titanium alloy was mainly affected by welding speed,wire feeding speed and interlayer spacing temperature.Among them,welding speed has the most prominent influence on the microstructure evolution process of titanium alloy,and the next was the interlayer spacing temperature,and the last was wire feeding speed.Mechanical properties of components by different process parameters were tested.The test results show that the mechanical properties of all components reach 80% of the base metal.When the welding speed was 0.25m/min,the wire feeding speed was 6.4m/min,the interlayer spacing temperature was between 70 < T < 100℃,the tensile strength of the components can reached 957.33 MPa and the elongation can reached 7.96%.The fracture of tensile specimen under different process parameters was observed,and it was found that the fracture forms of the members were dimple fracture.