Microstructures And Mechanical Properties Of TC4 Forged Part Repaired By The Technology Of Point-mode Forging And Laser Repairing

TC4 titanium alloy,also known as Ti6Al4 V,with the main alloying elements of aluminum and vanadium,is an α+β titanium alloy with high fracture toughness,low density,high strength,excellent corrosion resistance and superior biocompatibility,making it ideal for applications in aerospace parts,biomedical implants and automotive components.With the advantages of controlled heat input to the damaged part and low repair cost,laser additive repair technology is gradually being used to repair damaged parts.Conventional laser repair of titanium alloys in the fused region results in the formation of coarse columnar crystals with anisotropic mechanical properties,limiting their production applications in different stress environments.In this experiment,a commercially purchased rolled TC4 titanium alloy sheet was repaired using a point-mode forging and laser repairing technique.Three different heat treatment regimes were used to treat the TC4 repair specimens,and the microstructure,microhardness,tensile properties,and fracture of the samples were explored and analyzed in depth for different repair regions and different heat treatment regimes.The results showed that the point-mode forging and laser repairing TC4 repaired samples consisted of repaired zone,heat affected zone and hot rolled substrate zone.The histomorphology of the three zones is continuous and gradual,with dense fusion in the joining zone.The macrostructure of the repair zone is fine and uniform equiaxed crystals with an average size of 150-350 μm,and the microstructure inside the grains is a mesh basket.The yield strength,tensile strength and elongation of the tensile specimens of the repaired area,the tensile specimens of 50% of the repaired volume sampled in the X-axis direction and the tensile specimens sampled in the Z-axis direction of the TC4 repaired parts by point-mode forging and laser repairing met the ASTM B381-2013 standard for titanium alloy forgings.After 550℃/4 h/AC,the microstructure of the repair zone and the matrix zone did not change significantly,but the mechanical properties tended to be similar.850℃/2 h/AC heat treatment,there was coarsening or spheroidization of the αphase of the lath in the repair zone,and the elongation of the repair zone and the matrix zone decreased sharply.After solution aging heat treatment at 940℃/2 h/AC+550℃/4h/AC,the microstructure of the repaired zone was a triplet consisting of equiaxed α phase,slatted α phase and β transition,and the specimens in the repaired zone and substrate zone were brittle and fractured.Point-mode forging and laser repairing TC4 repair samples should not choose a heat treatment regime with too high a temperature.