Study on fast gas forming with in-die quenching for titanium alloys and the strengthening mechanisms of the components

The rapid development of the aerospace industry has led to a dramatic increase in the demand for complex thin-walled structural parts made of titanium alloys. However, the huge energy consumption and high cost of the existing forming process seriously limit their widespread application. In this paper, a new forming process of Fast Gas Forming with in-die Quenching (FGFQ) for titanium alloys is developed, in which the tube blank is heated by a current in tens of seconds and the pressurization rate is up to 20 MPa/s. The formed component could be significantly strengthened by the formation of abundant fine martensitic microstructure during in-die quenching. For example, the yield strength and tensile strength of the Ti-3Al-2.5V alloy component increase by 26.5% and 15.2% respectively, and the elongation is still up to 16.2%. The effects of current density, forming temperature, pressurization rate, and forming pressure on temperature distribution, forming accuracy, and mechanical properties of the components are investigated through the combination of FEM simulation and experiment. In FGFQ, the tubes are formed at a high strain rate above 4 s-1 and quenched in die with a cooling rate above 100 °C/s. The entire forming cycle can be controlled within 1 min. This study demonstrates the great potential of FGFQ in manufacturing thin-walled titanium alloys components with a dramatically improved efficiency and significantly reduced energy consumption. It also provides a new strategy for strengthening titanium alloy components by fine martensitic microstructure.