THE EFFECT OF STRAIN, STRAIN RATE AND TEMPERATURE ON FORMABILITY OF TI-6AL-4V ALLOY

Ti-6Al-4V is the most widely used titanium alloy. It combines attractive properties with inherent workability which allows it to be fabricated into complex shapes. It is used for aircraft gas turbine disks and blades. It is also extensively used for aircraft structural components and other applications requiring strength and temperature up to 315-degrees-C. During forming, a material's inherent ability to distribute strain is coupled with its forming limit to determine its overall formability. Although the contribution of these two elements change in a complex manner with the nature of the external stress gradient, the object of this work is to examine formability dependence on material properties, normally the strain hardening exponent n(n=d Ln-sigma/d Ln-tau) and the strain rate sensitivity m (m=partial derivative-Ln-sigma/partial derivative-Ln-epsilon). These latter two material parameters were therefore determined for the Ti-6Al-4V alloy sheet at room temperature and 540-degrees-C for strain rates of 3x10(-4), 3x10(-3), 3x10(-2) and 3x10(-1) s-1. The experimental values for n and m were used to predict the forming limit diagram (FLD).