Microstructure And Properties Of Al-Sm Alloy For Fermi Chopper

With the development of domestic neutron detection technology,various neutron devices have put forward new requirements for neutron absorption materials.For example,slit devices such as Fermi choppers require ultra-thin foils with high neutron absorption rates.The traditional scheme of using polyester film to coat 10B4C/Gd2O3 to manufacture a neutron absorption film has the disadvantages of easy peeling of the coating and poor overall uniformity of the film.In order to solve the existing problems,this topic uses the metal material with high neutron absorption cross section to prepare a neutron absorption foil with the advantages of strong plasticity,good processability and high neutron absorption rate.Sm is selected as neutron absorbing nuclide,and its macro neutron absorption cross section is 5600 barn,which is about 1.5 times that of 10B(3800 b).A new neutron absorbing material with the advantages of low cost,high plasticity and high neutron absorption rate can be prepared by adding Sm to Al with excellent plasticity.The neutron absorptivity and plasticity of Al-Sm alloys are closely related to the Sm content.The paper firstly uses the MCNP simulation to calculate the influence of the Sm content and material thickness on the neutron absorptivity,and determines that the research objects are Al-5Sm,Al-10Sm,Al-15Sm and Al-20Sm,The alloy composition is in mass percentage.Al-xSm(x=5,10,15,20)were prepared by vacuum induction melting,and the as-cast and heat-treated Al-xSm(x=5,10,15,20)alloys were discussed.The microstructure and phase transformation of Al-Sm alloys with different compositions were studied by XRD,EDS and SEM.The results show that there are a lot of eutectic microstructure in the cast microstructure of Al-Sm alloy.Al-5Sm and Al-20Sm prepared by rapid cooling are mainly composed of ?-Al and high temperature phase ?-Al4Sm.The second phase of Al-10Sm and Al-15Sm prepared by slow cooling is mainly composed of low temperature phase ?Al4Sm?After heat treatment at 550?/2 h,the second phase undergoes an allotropic transformation ?-Al4Sm??-Al4Sm.After heat treatment at 550?/300 h,the ?-Al4Sm decomposed into Al3Sm.The changes in the micromechanical properties of the matrix phase and the second phase of the Al-Sm alloy as cast and heat treated were studied by nanoindentation method.The results show that the heat treatment has little effect on the microhardness of the Al-Sm alloy matrix phase ?-Al,while the three There are some differences in the microhardness of the second phase.The microhardness of ?-Al4Sm,?-Al4Sm and Al3Sm were 8.97 GPa,8.91 GPa and 9.89 GPa.Al-xSm(x=5,10,15,20)alloy foils were prepared by forging,hot rolling and cold rolling,the processing technology of Al-Sm alloy was explored,The homogenization annealing temperature of Al-Sm alloy was determined to be 550? by differential scanning calorimetry(DSC).The processing technology of Al-5Sm and Al-10Sm is different from Al-15Sm and Al-20Sm.The forging temperature of Al-5Sm and Al-10Sm is about 510?,the reduction amount per fire is about 40%,the hot rolling is selected with large reduction(40%)deformation,the rolling temperature is 520?,and the cold rolling annealing process is selected as 400?/2 h,select 50%of the pressure for each pass.Al-15Sm and Al-20Sm alloys contain large-sized lath-like second phases,and the plasticity is poor.The forging temperature is about 570?,and the reduction amount per fire is about 20%.Hot rolling is suitable for small reduction and multi-pass deformation.The reduction amount between annealing is controlled at 20%,the rolling temperature is 580?,the cold rolling annealing process is selected at 400?/2 h,and the reduction amount for each pass is selected as 30%.After forging,hot rolling and cold rolling,Al-Sm alloy is finally prepared into foil with thickness of 0.03 mm.Compared with as-cast alloy,the second phase of Al-Sm alloy prepared into foil is more evenly distributed,and the original strip-shaped second phase is broken and smaller in size.Such microstructure improves the mechanical properties of foil,and profit neutron absorption.Through a series of processing techniques,it is found that Al-10Sm and Al-15Sm have high yield while ensuring neutron absorption.After the neutron transmission experiment,it is found that when the Sm content is the same,the neutron absorptivity increases with the increase of material thickness.When the material thickness is the same,the neutron absorptivity increases with the increase of Sm content,and the measured value of neutron transmittance of the material is in good agreement with the MCNP simulation results,which meet the requirements of neutron absorption performance.