Study On Heat-treatment And Cold-forging Process Of TC16Titanium Alloy

TC16titanium alloy fastening piece produced by cold forging process has nice mechanical properties, well production effiency and ideal cost. And the process is suited for mass production. In the present work, effects of heat treatment and cold forging deform behavior on TC16titanium alloy were studied.In this paper, optical microscope (OM), X-ray diffract meter (XRD) and transmission electron microscope (TEM) had been used to study the phase composition and structure evolution during the heat treatment (including annealing, solution treatment and solution aging treatment) and cold forging deformation process. Scanning electron microscope (SEM) was used to analysis the cold forging fracture. Cold forging technology was optimized and fracture mechanism of TC16alloy was studied. The results were as follows:(1)The temperature of annealing had marked affect on material structure and properties. With the increasing of annealing temperature, the material structure transformed from equiaxial microstructure to duplex microstructure. When the temperature was beyond860℃the structure transformed to bulky Widmanstatten structure with poor plasticity. To keep good plasticity, the material should be annealed at800℃for2h and furnace cooling to550℃and then air cooling to room temperature.(2) Solution aging treatment could strikingly improve the strength by dispersion effect, but it also degraded the plasticity. Solution treated at800℃for2h and then artificial aging treated at560℃for6h could make the material strength up to1250MPa, which was the level of high strength steel. Thus, the material can be used to make fastening piece with high strength requirement.(3) Deformation shear zone with high stiffness because of high dislocation density would appear in the centre of Ti alloy samples during cold forging. The crystalline grains in the shear zone were seriously flattened. The results demonstrated that the deformation was mainly because of the dislocation sliding, and the structure and properties of the deformation samples presented a certain extent of inhomogeneity. When the ratio of forging was1/6, the hardness was300HV which was stabilized.. The original equiaxed crystals in the central part of the shearing band was stretched gradually with the increase of the deformation. Grain crack and refinement occured when the grain width was less than100nm, which was the main reason of the stable hardness.(4) Martensitic transformation which could affect the properties of fastening piece occurred in the deformation structure and it should be eliminated by annealing. Because of good plasticity of TC16titanium alloy, cracks didn’t appear in the microstructure during cold upsetting process. Surface crack appeared when the forge ratio reached1/6, which was caused by surface tension. Through optimize the material structure and cold upsetting technology, the eligibility ratio of TC16titanium alloy fastening piece could be strikingly improved.