Studies And Improvement On The Microstructure Uniformity Of TC1 Titanium Alloy Sheet

The nominal chemical composition of TC1 titanium alloy is Ti-2Al-1.5Mn.The strength of TC1 is slightly higher than that of industrial pure titanium,and it has good process plasticity,thermal stability and welding properties.It is widely used in aerospace,civil and other fields,and is often used to prepare aircraft fuselage skin.Tail fairing and aero-engine housing and insulation cover.Most of the semi-finished products of TC1 titanium alloy is TC1 sheet.When testing the microstructure of TC1 sheet,it is often found that there is a phenomenon of uneven organization.The cause of the formation of this kind of uneven structure,the influence and the improvement method are not clear.Therefore,the study of microstructure uniformity of TC1 sheet has important industrial application value.In this paper,the evolution of microstructure in the rolling process of TC1 sheet was studied,with emphasis on the microstructure characteristics of uneven microstructure and its effect on the mechanical properties of the sheet.Through the study of hot rolling and cold rolling,The effect of annealing and other factors on the microstructure uniformity,optimize the rolling process parameters,improve the microstructure uniformity of TC1 sheet,the main results are as follows:The uneven microstructure of TC1 sheet occurs in the stage of hot rolling billet opening,which is due to the dynamic recovery of acicular α grain in the microstructure of the slab during hot deformation,and a large number of subcrystals are produced inside.These recovered subcrystals did not recrystallize and grow during subsequent annealing,and the black β phase diffused along the subgrain boundary,so it showed black banded structure under optical microscope.The distribution of banded structure in the same sheet is not uniform,and its distribution law is related to the uneven deformation during rolling.The more uneven the deformation is,the higher the distribution density of banded structure is,which shows the hardness of this part in mechanical properties.The higher the strength,the lower the plasticity,and the greater the difference between longitudinal and transverse properties.The results of hot rolling process test show that the microstructure uniformity of TC1 sheet can be significantly improved by heating in single phase zone and opening billet in two phase zone,and the microstructure uniformity of TC1 sheet can be improved by increasing the cold rolling deformation to more than 50%.The results of annealing process show that the microstructure uniformity of TC1 sheet can not be improved by Heat preservation 0.5h~1h at 740℃~780℃.Considering the results of hot rolling,cold rolling and annealing,it is determined that the annealing process of hot rolled billet at 950 ℃,cold rolling deformation at 50% and annealing at 740℃/30 min is the optimized TC1 sheet production process.The microstructure of TC1 sheet rolled by this process are uniform and the mechanical properties are fine.