Microstructural Evolution And Property Research Of ?-T51Z Alloy In The Process Of Hot Deformation And Heat Treatment

Compared with traditional aeronautical structure materials such as high-strength steel and titanium alloy,zirconium and zirconium alloys become potential structural material in aerospace vehical due to their small thermal neutron absorption cross section,excellent radiation and corrosion resistance.In this paper,T51Z(51.1Zr-40.2Ti-4.5Al-4.2 V)alloy was used as the research object,The effects of different thermal deformation parameters and heat treatment processes on microstructural evolution and mechanical properties of T51 Z alloy were studied by techniques such as X-ray diffraction(XRD),electron backscattered diffraction(EBSD),including:The hot deformation behaviors and microstructural evolution of as-casted and ?-quenched T51 Z alloys under different deformed temperatures and strain rates were sdudied.EBSD and OM and TEM results showed that the compressing curves of as-casted and ?-quenched T51 Z alloys in hot deformation had a typical characteristic of single-peak dynamic recrystallization.Based on the peak stress,the constitutive equations and activation energy of thermal deformation of as-casted and ?-quenched T51 Z alloys were established.At the same time,the hot working diagrams of as-casted and ?-quenched T51 Z alloys were established.The deformed temperature and strain rate had a great influence on the deformation microstructure,as-casted and ?-quenched T51 Z alloys were more easier to occur dynamic recrystallization with increase of deformed temperatures or decrease of strain rates,but dynamic recrystallization did not proceed sufficiently and the distribution of recrystallized grains were not uniform.Based on the hot working diagrams and processing parameters which were gained from above studies,microstructural evolution and mechanical properties of T51 Z alloy under the processes of forging,s hot rolling,annealing were studied systematically.The results showed that the forged alloy consisted of broken ? grains,and a large number of paralleled laths of ? appeared grain boundaries,the strength of forged alloy was 1640 MPa but the plasticity was 2.13%.After solid solution in 850°C/0.5h and water quenching,which were mainly composed of equiaxed ? grains with different sizes and had good ductility,the elongation was 13.39%.In the process of hot rolling,most grains in RD-ND plane were elongated obviously along the rolling direction and broken grains were unevenly distributed between the elongated grains;The RD-TD plane had not obvious morphology of elongated grains,and the average grain size decreased gradually with amount of total rolling deformation;The ND-TD plane distributed many elongated grains along the transverse direction,the overall grain size was not uniform.With increase of amount of total rolling deformation,the strength of different hot-rolled alloys increased from 1308.69 MPa to 1468.83 MPa but the elongation decreased from 0.96% to 0.42%.T51 Z alloy After annealing,the microstructures of T51 Z alloys were equiaxed ? grains.And with increase of amount of total rolling deformation,the grain sizes in alloys with annealing of primary hot rolling and annealing of secondary hot rolling and annealing of final hot rolling were getting smaller and smaller,and the strength was getting higher and higher.The mechanical property in annealing of final rolling was the best,and the yield strength,tensile strength and elongation were 823.53 MPa,1110.10 MPa and 8.20% respectively.Ductile fracture was the main fracture mechanism of annealed alloys.