Titanium alloys offer the advantages of low density, high specific strength, and good corrosion resistance, making them widely used in aerospace, ocean engineering, military medicine, and other fields. However, the high cost, low thermal conductivity, and low elastic modulus of titanium alloys result in poor quality, low efficiency, and high cost of traditional processing, which seriously restricts their application and development. Plasma-arc additive manufacturing technology provides a cost-effective solution with high deposition and material utilization rates, which is crucial for the production of large and complex parts. However, owing to the high energy density of the plasma arc and the low thermal conductivity of titanium alloys, the formability of titanium alloy-deposited parts is compromised, resulting in the growth of coarse columnar grains. In addition, the characteristics of many parameters and the difficulty in controlling plasma-arc additive manufacturing limit the rapid formulation of additive manufacturing process parameters that meet mechanical standards. The influence of plasma arc additive manufacturing of Ti-6Al-4V alloy process parameters on formability, microstructure, and microhardness was investigated by orthogonal experiments, metallographic analysis, and characterization of the relationship between the microstructure and mechanical properties. The experiment was conducted in an inert argon gas environment using a plasma arc additive manufacturing system, which consists of a Kuka robot, main power supply, plasma power supply, and wire feeding system. The main process parameters included deposition speed, wire feeding speed, pulse base current, pulse peak current, pulse frequency, and duty cycle. The three main evaluation parameters of formability were evaluated using the melting width, reinforcement, and aspect ratio of the deposited layer as indicators. In addition, the average grain size and microhardness were used as indices to evaluate the effect of microstructure on mechanical properties. The results indicate that the degree of influence of the plasma arc process parameters on the formability is as follows: base current (Ib) > peak current (Ip) > duty cycle (Idcy) > wire feed speed (TWFS) > deposition speed (Ts) > pulse frequency (FP). Ib has the greatest influence on the deposited width, deposited height, and formability of a single layer, with a more pronounced effect when Ib is 50%-70% Ip. The deposition speed and duty cycle exhibited the following relationships: the faster the deposition speed, the smaller the width and height of the deposition layer. The effect of the duty cycle on the width and formability of the single-pass deposited layers was positively correlated. The effect of process parameters on the average grain size was Ts>FP>TWFS>Ib>Ip>Idcy , with larger deposition speeds resulting in smaller grain sizes. Pulse frequency was the second most influential parameter on average grain size, demonstrating that pulse disturbance aids in grain refinement. Moreover, the degree of influence of the process parameters on microhardness was Ts > Idcy > TWFS > Ib> FP > Ip. The deposition speed had the greatest influence on average grain size and microhardness, with Ip having limited influence on these two aspects. Although the influence of the deposition speed on microhardness was the greatest, the degree of influence was only 4%, indicating that the influence of the selected plasma-arc process parameters on microhardness was not significant. These findings provide a theoretical basis for plasma arc additive manufacturing and additive remanufacturing processes and offer technical support for the rapid repair of damaged parts in applications such as field mining machinery, marine ships, engineering equipment platforms, and petroleum and chemical equipment.
