Laser shock peening is combined with laser additive manufacturing to modify the surface microstructures and mechanical properties of as manufactured Ti6Al4V titanium alloy. Microstructural evolution, microhardness distribution, residual stress distribution and mechanical properties are examined before and after LSP. After peening, the interplanar spacing of lattices of both α and β phases decreases without any new phase formation. Grain refinement is achieved with average grain size of α phase decreasing from 33.6 to 24.3 μm. High density of dislocation lines, tangles, and multi-directional mechanical twins are observed. Residual stress is turned from tensile to compressive state with an affected depth of around 700 μm. The hardening layer reveled by microhardness is around 900 μm in depth. Grain refinement accounts for the yield strength, ultimate tensile strength, and elongation enhancements after peening.

Laser shock peening of laser additive manufactured Ti6Al4V titanium alloy

Thin plates are extensively used in automotive, shipbuilding, and railway industries. Welding technology is the main assembling method to manufacture thin plate structures because of its high productivity and ease of use. Consequently, residual stress and distortion induced by welding are an inevitable part of the manufacturing process in welding thin plate structures. Relatively low stiffness, and a high amount of heat input are the main reasons for distortion of the welded structures. In order to decrease the heat input, laser-based welding processes that generate highly localized heat with a very high intensity can be a good choice as an alternative to traditional fusion welding. To predict residual stress and distortion in welding thin plate structures, a three dimensional, thermo-metallurgical-mechanical finite element method was developed. The results of three different laser-based welding processes including aspects of Autogenous Laser Welding (ALW), Cold Wire Assisted Laser Welding (CWLAW), and Hybrid Laser-Arc Welding were compared with traditional Submerged Arc Welding (SAW) from both predicted and experimental perspectives. SYSWELD commercial code was used for the simulations in which both large and small deformation theories were employed to predict the residual stress and the final deformation. Experiments were executed to verify the simulation results. A digital high-resolution microscope was used to visualize and measure the weld cross- sectional shape and bead geometry. To measure the residual stress, an X-ray diffractometer was employed. A digital Vernier Caliper and a 3D laser-handheld scanner were used to measure displacement in the z-direction. Moreover, the mechanical properties of welds obtained by different welding processes were also verified by tensile and micro-hardness tests. It was concluded that lower heat input can markedly influence the final distortion of the welded structure. This conclusion can strongly support the idea of replacing traditional arc welding method with a laser-based one. Simulation and experimental results were matched fairly.

Numerical simulation and experimental validation of residual stress and welding distortion induced by laser-based welding processes of thin structural steel plates in butt joint configuration

https://www.research.manchester.ac.uk/portal/files/65058553/OLEN_5119_edit_report.pdf

Ahmed Elmesalamy

Papers

A comparison of residual stresses in multi pass narrow gap laser welds and gas-tungsten arc welds in AISI 316L stainless steel