Study On The Influence Of Sc On The Mechanical Properties And Thermal Stability Of Al-Cu-Ni Alloy

Cast aluminum alloys have the advantages of high specific strength,resistance to heat exposure,and low cost,making them ideal materials for aerospace and automotive applications.However,with the rapid development of science and technology,higher requirements of aluminum alloys were proposed in recent year.Therefore,the development of high-strength and lightweight heat-resistant cast aluminum alloys has gradually become a research hotspot.In this paper,based on casting Al5Cu1.5Ni alloy,the effect of microalloying of Sc element on the microstructure and mechanical properties of cast Al-Cu-Ni alloy is studied,and high-strength Al-Cu-Ni alloy is prepared by cold rolling deformation and microalloying strengthening effect of Sc element.In current research,with the purpose of study the thermal stability,Al-Cu-Ni alloys with and without Sc were explored the high temperature tensile test and heat exposure test,the main conclusions are as follows:（1）Sc elements can effectively refine the grains and second phases of cast Al5Cu1.5Ni alloys,thereby significantly improving the tensile properties of the alloys.Compared with the as-cast Al5Cu1.5Ni alloy,the average grain size of the as-cast Al5Cu1.5Ni0.3Sc alloy decreased by 42.5%,and the yield strength and tensile strength increased by 84.56%and 35.6%,respectively.T7 heat treatment has a significant strengthening effect on both alloys,but the alloy modified by Sc element still has higher yield strength and tensile strength in T7 state.The room temperature tensile test also found that Sc element modification and T7 heat treatment can effectively inhibit the plastic instability of the as-cast Al5Cu1.5Ni alloy.（2）After rolling deformation process at room temperature,the grains of Al5Cu1.5Ni alloy and Al5Cu1.5Ni0.3Sc alloy in T7 state are flat strips,the grain boundary area increases,and the second phase transforms from larger continuous strips to smaller particles.Obviously,a large number of dislocation cells are generated inside the grains.With the respect to the STEM-EDS and SEAD analysis,it is found that the second phases in the two alloys are Al₃Ni₂,Al₂Cuand Al₂CuNi,and the T7 state Al5Cu1.5Ni0.3Sc alloy also contains Al₃Sc.Compared with cold-rolled deformed T7Al5Cu1.5Ni alloy,Al5Cu1.5Ni0.3Sc alloy has a higher dislocation density.After cold rolling deformation,the yield strength,tensile strength and elongation of T7 state Al5Cu1.5Ni alloy increased by 98.12%,45.63%and 59.24%respectively.The yield strength,tensile strength and elongation of T7 state Al5Cu1.5Ni0.3Sc alloy increased by 85.16%,42.86%and 99.71%,respectively.（3）Sc elements can improve the high-temperature tensile properties and heat resistance of the alloy,and inhibit the plastic instability of the alloy,and the major founds can be divided into the following points.Firstly,the high-temperature tensile experiment shows that the tensile strength of Al5Cu1.5Ni alloy and Al5Cu1.5Ni0.3Sc alloy in T7 state decreases slightly with the increase of temperature,but the properties of T7 state Al5Cu1.5Ni0.3Sc alloy is higher than that of T7 state Al5Cu1.5Ni alloy at various temperatures,and the room temperature tensile properties is still 79%when stretched at 300°C.After cold rolling deformation,the high-temperature tensile properties of both alloys decreased significantly,but the cold-rolled deformed T7 state Al5Cu1.5Ni0.3Sc alloy was still slightly higher than that of cold-rolled deformed T7state Al5Cu1.5Ni alloy.Secondly,T7 state Al5Cu1.5Ni alloy and Al5Cu1.5Ni0.3Sc alloy did not change significantly after 10～100 hours heat exposure treatment at 300°C.The mechanical properties of both alloys decreased significantly after 10 hours heat exposure.When the heat exposure time extended to 30 hours,the tensile properties of the two alloys tended to be stable.Among them,the yield strength and tensile strength of T7 state Al5Cu1.5Ni0.3Sc alloy decreased less than that of T7 state Al5Cu1.5Ni alloy.After 100 hours heat exposure treatment of the two alloys,the size of the white needle-like precipitated phase in the matrix of T7 state Al5Cu1.5Ni0.3Sc alloy was significantly smaller than that of Al5Cu1.5Ni alloy,indicating that the Sc element could inhibit the coarsening of the matrix precipitated phase after heat exposure treatment of T7 state Al5Cu1.5Ni alloy.The microstructure of the two alloys deformed by cold rolling has undergone significant changes after heat exposure treatment.The mechanical properties decreased significantly,and gradually stabilized with the increase of heat exposure treatment time.Finally,the tensile curve analysis results indicated that the T7 state Al5Cu1.5Ni alloy showed jagged fluctuations after heat exposure treatment,and the fluctuations became more and more obvious with the extension of treatment time.T7 state Al5Cu1.5Ni0.3Sc alloy also showed jagged fluctuations after 30 hours heat exposure,but the fluctuation amplitude was small and changed first strengthened and then weakened.The tensile curves of the two alloys deformed by cold rolling showed jagged fluctuations at different heat exposure treatment times,and the fluctuation amplitude was almost the same.In summary,Sc element can improve the mechanical properties of Al5CuNi alloy,inhibit the rapid plastic instability of the alloy,and improve the thermal stability of the alloy.