Effect of pre-strain on microstructure and stamping ability of TA2 titanium alloy and H260 low-alloy steel

Abstract

Applying pre-strain can not only change the microstructure and the mechanical property of metal material but also affect sheet metal stamping ability. In this paper, taking H260 low-alloy steel and TA2 titanium alloy as experimental materials, pre-strain ranging from 0 to 0.16 was applied using the one-step and the multi-step method respectively. Microstructure observation, tensile test, bending test, and cup bulging test were conducted on the pre-strained samples. Results show that in the pre-strain loading stage, the slipping and twinning deformation occurs in the TA2 alloy sample while dislocation sliding mainly happens in H260 low-alloy. With pre-strain increasing, the product of ultimate tensile strength and elongation rate gradually decreases, and the true ultimate tensile stress and accumulating elongation change rarely. The “product of yielding strength and elongation rate” can be enhanced by applying a pre-strain of 0.04 on the condition that plasticity is still at a high level. In the pre-strain range of 0 - 0.16, a bending test with a 30.8 °-opening angle can be completed on H260 steel. The springback angle changes from negative to positive with an increase in pre-strain. The bending ability of TA2 titanium alloy is very poor, for a crack can easily occur even in the original sample. The cupping value decreases gradually with an increase in pre-strain. The cupping value of TA2 titanium alloy is higher than that of H260 low alloy steel for the constant pre-strain. A quite large difference exists between the two experimental materials. Pre-strain loading pass has no significant effect on the microstructure evolution, mechanical properties, and stamping properties.