Characterization of the deformation behavior and microstructure evolution in laser bending of TC4 titanium alloy heavy plate

Abstract

A new plastic processing method for laser bending of TC4 titanium alloy heavy plates was developed in this work. Different from previous studies, the thickness of the plates in this work reached 6 and 12 mm. High-energy laser beam was applied on the surface of the TC4 titanium alloy heavy plate, resulting in thermal stress on the surface of the plate and causing bending deformation. The microstructure and mechanical properties of the bended plates were investigated. A finite element model was also developed to simulate the laser-assisted bending process of the TC4 titanium alloy heavy plate. The microstructure observation indicates that the original α + β worm-like microstructure changed to basket-weave microstructure composed of α′ phase of acicular martensite after laser bending. This microstructure with high densities of dislocation and twinning played an important role in grain boundary strengthening. Therefore, the hardness of the center of the heat-affected zone > the hardness of the base metal > the hardness of the edge of the heat-affected zone after bending. The tensile strength of the heat-affected zone is not significantly different from that of the base metal, but the tensile elongation is slightly lower than that of the base metal and its plasticity is lower. The simulation implies that temperature gradients in the normal direction caused by laser scanning can stimulate a horizontal partial stress σx. The variation of σx causes the plate form a bending angle after laser scanning.