Investigation On The Control Of Microstructures And Mechanical Properties Of Novel Zirconium Aluminum Binary Alloy

Zirconium?Zr?and its alloys are widely used as structural materials in nuclear power and chemical industries owing to their low thermal neutron absorption cross section and excellent corrosion resistance.Zr also possesses some other advantages,such as lower density than Ferrum?Fe?,lower thermal expansion coefficient than Titanium?Ti?,good bio-compatibility,non-magnetic and high melting point,etc.,and can be used as structural materials in aerospace,shipping,and biomedical industries.However,the existing Zr alloys are studied and developed as cladding material for nuclear fuel.Due to the limitations of thermal neutron economy and corrosion resistance,the types and amounts of alloying elements of nuclear Zr alloys have been greatly limited and result in the difficulty of enhancing the mechanical properties of nuclear Zr alloys.Moreover,the raw material for nuclear Zr alloys is atomic energy-level sponge Zr which is very expensive,and limits the applications of nuclear Zr alloys in other industries.Aluminum?Al?is a low-cost and abundant industry metal which is widely used as alloying element to strengthen Ti alloys.Zr and Ti belong to the same group of elements and have the same outer electronic arrangement.They have similar physical and chemical properties.Therefore,it can be deduced that the excellent strengthening effect of Al may be also suitable for Zr.In addition,Al is an?-phase stabilizer and can significantly increase the transition temperature of Zr,which is beneficial for Zr alloys to obtain globularized microstructure with better mechanical properties after deformation at high temperature.Therefore,Al was selected as the alloying element,and low-cost industrial pure Zr from which hafnium?Hf?was not removed was used as raw material to prepare novel low-cost ZrAl binary alloys in this study.A series of investigations on the control of microstructures and strengthening mechanisms of binary ZrAl alloys were systematically conducted.In order to study the effect of Al contents on the microstructures and mechanical properties of hot-rolled ZrAl binary alloys,ZrAl binary alloys with various Al contents were prepared and hot-rolled at 870°C,and then the characterizations of microstructures and mechanical properties were conducted.The results show that when the Al content exceeds9at.%,dynamic precipitation of Zr₃Al will occur in the alloy during hot rolling process.The precipitated Zr₃Al particles distribute on the?grain boundaries and promote the refinement and globularization of?grains.In addition,the precipitation of Zr₃Al phase will cause the exsolution of?matrix and the formation of high-temperature?phase.This high-temperature?phase can be retained at room temperature after quenching.The test results of mechanical properties show that the yield strength,tensile strength and fracture elongation of hot-rolled Zr–12Al?at.%?alloy increased 341.3MPa,343.8MPa,and 2.2%,respectively,compared with the hot-rolled pure Zr.Analysis show that the main strengthening mechanism of hot-rolled ZrAl alloy is solid solution strengthening.Moreover,the precipitation of Zr₃Al significantly improves the work hardening ability of alloys.In order to further investigate the mechanism of plasticity enhancement of hot-rolled Zr–12Al alloy,the microstructures before and after deformation were studied by electron backscattered diffraction?EBSD?technique.The results show that the Zr₃Al phase with a L1₂ structure exhibits excellent deformation ability,which will coordinate the deformation of the matrix during the deformation,and avoid premature of crack formation during the work hardening stage.In order to solve the problem of poor stability and repeatability of the mechanical properties of hot-rolled Zr–9Al?at.%?alloy.After a series of comparative experiments,it was found that the mechanical properties of hot-rolled Zr–9Al alloy was sensitive to the interval soaking time between each pass during the rolling process.Therefore,the influences of the interval soaking time between each pass on the microstructures and mechanical properties of Zr–9Al alloy were systematically studied.The results show that dynamic precipitation will take place during hot rolling when the interval soaking time is 5 min,and Zr₃Al and?phases were formed at grain boundaries.The dynamic precipitation behavior will lead to the refinement of grains,enhancement of globularization and increase of dislocation contents of Zr–9Al alloy,which increase the strength and plasticity of the alloy.Studies have shown that Zr alloys with globularized microstructures exhibit excellent comprehensive mechanical properties.Therefore,two different globularization processes,dynamic and static globularizations,were designed to process Zr–9Al alloys.The microstructures and mechanical properties of the alloys after above-mentioned two globularization processes were systematically studied.The results show that the microstructure of Zr–9Al alloy after dynamic globularization consists of approximately equiaxed?grains.However,the Zr–9Al alloy after static globularization consists of thick?grains with irregular morphologies,showing an obvious{101?0}<112?0>texture.In addition,a large number of twins were observed inside the?grains of the Zr–9Al alloy after static globularization.Mechanical tests show that the yield strengths of these two alloys processed by different globularization processes varies by 25.2 MPa.Analysis shows that though the grain sizes of these two alloys processed by different globularization processes have obvious differences,Hall-Petch mechanism does not work due to the large grain sizes.Meanwhile,the texture of the alloy after static globularization does not result in the difference of yield strength between these two alloys.