Increasing the capability of laser peen forming to bend titanium alloy sheets with laser-assisted local heating

Abstract

The present work proposes a new process to bend high-strength titanium alloy by laser peen forming (LPF) with laser-assisted local heating. In experiments, a nanosecond pulsed laser and a CW fiber laser for laser peening and heating, respectively, were arranged to irradiate the top and bottom sample surfaces coaxially. Laser heating beam moved along with the laser-shock loading in a synchronized way to cover a specified area. Different powers of fiber laser output were used in experiments to investigate heating effect on the bending deformation and microstructure change of Ti6Al4V alloy. It is proved that the proposed process is an effective way to improve the bending capability of LPF through increasing the plastically-deformed layer induced by the dynamic loading. And the radius of bending curvature is found to decrease greatly by increasing laser heating power. Although laser heating would provide an extra plastic deformation on the opposite side of laser peening to increase the convex bending simultaneously, the generated alpha-case and small cracks close to heating surface are detrimental to fatigue strength and ductility. Therefore, only the temperature effect to decrease the material strength is acceptable in LPF with laser-assisted local heating to increase the bending deformation & of titanium alloy.