Simulation And Microstructure Analysis Of Al-4.5cu Alloy Solidification Process At Different Cooling Rates

The cooling rate during the solidification process has significant influence on the solidification structure and mechanical properties of the alloy.In this study,the high cooling rate obtained by the thin strip casting and rolling experiment shows that the cooling rate plays a key role in controlling the average grain size of the casting,the distance between the secondary dendrite arms,the number of eutectic phases,the density of precipitated phase,and the degree of solute in the-Al matrix.Therefore,it is very important to quantitatively elucidate the effect of different cooling rates on the solidification structure and mechanical properties of alloys with a wide crystallization range.In this paper,the typical Al-4.5wt.%Cu alloy as the research object,adopt the sand mold casting,water-cooled copper casting,such as twin roll strip roll casting process,achieved with different cooling rate,sample preparation,and combined with the solidification process of phase field and solute field simulation methods,such as exploring the cooling rate and the corresponding relation of solidified structure and distribution of solute elements.Finally,it provides a certain research basis for the successful preparation of high-quality aluminum alloy plates based on subrapid solidification.The main work and research results of this paper are as follows:.(1)The influence of technological parameters of double roll strip casting and rolling on slab quality was studied.The temperature field of thin strip casting and rolling process under different technological parameters was analyzed,and the optimum technological parameters were determined as follows:the optimum casting temperature of 6 mm rolling plate was 700?,and the casting and rolling speed was 1.05 m/min.The.optimum casting temperature and casting speed of 3 mm rolling plate are 690? and 1.50 m/min.At this time,the depth of liquid cavity is appropriate and the melt flow is even in the two-phase zone.(2)The corresponding relationship between cooling rate and secondary dendrite arm spacing and composition distribution was explored.The cooling rates at different positions of the slab were calculated,in which the surface cooling rate of the 6mm slab was 117.3 ?/s and the surface cooling rate of the 3mm slab was 273.5?/s,both of which were within the range of sub-rapid solidification cooling rate.The average grain size decreased from 309 m in sand mold to 95 m in thin strip casting with increasing cooling rate.The solid solution degree of Cu element in the matrix increases,and the area fraction of intercrystalline eutectic phase decreases.In a 6 mm slab,the content of Cu element in some areas is only 4.57%,and the eutectic phase morphology is intermittent and discretized,and the concentration gradient of intercrystalline solute element decreases.(3)Segregation behavior of solute elements during solidification of slab with different thickness was analyzed.Solute field results show that the macroscopic segregation of Cu element in the core of cast and rolled slab is very obvious,which is consistent with the experimental law.Among them,the content of Cu element in the center of 6mm slab reaches 17Wt.%,while that in the center of 3 mm slab reaches 25Wt.%.According to the analysis,this is because when the slab thickness is relatively thin,the solid-liquid interface migrates at a faster rate,and the element rich area is "submerged" before sufficient diffusion,resulting in more solute element rich area,that is,the macro segregation defect.(4)The effect of cooling rate on the microstructure and properties of heat-treated alloy was studied.The homogenization kinetic equation was derived,and the theoretical time for homogenization of samples with different cooling rates was 23.5 h,13.5 h,7.1 h and 5.2 h,respectively.With the increase of cooling rate,the trend of eutectic morphology melting and spheroidization is enhanced,the degree of decomposition and backdissolution is increased,and the time required for complete homogenization is shorter,and the mechanical properties after aging treatment are also improved to some extent.