Horizontal Continous Casting Technology Of Cu Based Metallic Glasses And Its Strenthening And Toughening

Although amorphous alloys have various excellent properties,their molding conditions are too harsh,and extremely high requirements are placed on the selection of alloy components and the cooling rate of the melt.The traditional molding technology of bulk amorphous alloys,such as copper mold casting methods,injection casting methods,suction casting methods and pressure casting methods often have problems such as low production efficiency,high raw material costs,and complex processes,making it difficult to meet the industrial production requirements for preparing large-size amorphous alloys.As a common method of industrial production,horizontal continuous casting technology has the advantages of high production efficiency,adjustable billet size,and easy automatic control.With the high cooling strength of the water-cooled copper mold,it can meet the continuous requirements of large-size amorphous alloy slabs manufacturer.Therefore,it is of great significance to explore the horizontal continuous casting process of amorphous alloys with excellent mechanical properties and low raw material costs.At present,there is little research on the numerical simulation of amorphous alloys at home and abroad.In the early stage of research and development of amorphous alloy preparation technology,the numerical simulation work is mainly through the single-roll stripping,double-roll rolling and copper mold casting method.The melt cooling rate is calculated to determine whether it meets the critical cooling rate of amorphous.At present,the research on the preparation of amorphous alloys by continuous casting method is still in its infancy.Therefore,the numerical simulation of horizontal continuous casting of amorphous alloys has played a positive guiding role in exploring the optimal continuous casting process.The plastic deformation of amorphous alloys relies on highly localized shear bands,which leads to plastic strains that only occur in a small shear deformation zone,and they often exhibit brittle fracture characteristics.Therefore,the study of strengthening and toughening methods of amorphous alloys is also a hot issue in the field of materials.By optimizing the annealing process and parameters,the composition,size and distribution of nanocrystals in the amorphous matrix can be controlled.The structural relaxation and nano-crystallization of amorphous alloys during isothermal annealing have a positive effect on the mechanical properties of the alloys.In view of the above problems,this paper selects Cu-based amorphous alloys as the research object,and uses graphite/water-cooled copper mold composite mold as casting mold.The horizontal continuous casting process of Cu-based amorphous alloys is studied and numerical simulation analysis and experimental verification are carried out.The strengthening and toughening mechanism of different heat treatment methods on bulk amorphous alloys.The main reseai-ch work of this paper are as follows:(1)The thermal conductivity,specific heat capacity,viscosity,glass transition temperature.liquid-solid phase line temperature and other thermophysical parameters of(Cu47Zr45Al8)98.5Y1.5 amorphous alloy have been measured,and ProCAST was used to perform numerical simulation analysis on the filling and drawing process of amorphous alloy continuous casting.The calculation results of the temperature field and the solidification percentage show that the filling time of the amorphous melt in the tundish is 22 s,and when the holding time exceeds 55 s,a thicker shell is formed at the drawing head,which is prone to drawing.(2)When the model embedding depth is 30 mm,the drawing speed is 1 mm/s,and the superheat is 80 K,the cooling rate of the melt before the temperature drops to Tl is less than the critical value of Cu-based amorphous alloy(20 Ks-1)and it is difficult to form an amorphous structure.When the drawing speed increases from 1 mm/s to 2?4 mm/s,the cooling rate of the melt before the temperature drops to Tl is greatly increased.At the same time,increasing the superheat of the drawing has a slight increase in the cooling rate of the melt.Improving the structure of the water-cooled composite mold and shortening the depth of the graphite embedded copper mold end to 10 mm?20 mm will help reduce the cooling time of the casting slab in the graphite,thereby increasing the cooling rate of the melt in the mold.(3)The Cu47Zr45Al8 amorphous alloy is prepared by double-chamber differential pressure horizontal continuous casting equipment.The drawing process is 4s-stop 4s,and the drawing speed is 2?4 mm/s.When the superheat is 80 K and 200 K,the slab matrix has obvious crystallization phenomenon,and a completely amorphous structure is not formed.Adding a small amount of Y element to the Cu-Zr-Al ternary amorphous alloy system improves the amorphous forming ability of the alloy.When the continuous casting superheat is 80 K,the core structure of the obtained slab is completely amorphous.Its room temperature compressive strength is 1803 MPa,and the fracture form is brittle fracture;when the continuous casting superheat is 50 K,a small amount of micron Y2O3 is precipitated in the slab,and nano-sized Cu10Zr7 and AICu2Zr phases are dispersed in the amorphous matrix.The compressive strength at room temperature is slightly lower than that of a completely amorphous cast slab,while the plastic strain is increased,and the fracture form is ductile-brittle mixed fracture.The Vickers hardness and impact toughness of the castings are(495.3±3.4)Hv and 5.73 J/cm2,respectively.(4)Apply f=21 KHz?E=200 V?I=20 A,f=18 KHz?E=180 V?I=20 A,f=15 KHz?E=180 V?I=15 A three different power magnetic fields to the amorphous continuous casting process,using small coil method to measure the magnetic induction intensity.Through comparison,it is found that when the frequency is 18 KHz,the internal magnetic induction intensity fluctuation of the coil is small,and the magnetic field distribution is more uniform.Under the action of the three kinds of electromagnetic fields,the diffuse scattering peaks are observed in the XRD patterns of the core structure of the cast slab between 35° and 45°,indicating that the core structure is completely amorphous.Observing the macroscopic morphology of the plate samples obtained at different frequencies after corrosion,the samples obtained under the action of an electromagnetic field of f=18 KHz have the highest amorphous content,and the fracture strength reaches 1890 MPa.(5)The step annealing process is used for(Cu47Zr45Al8)98.5Y1.5,and liquid nitrogen chilling is used instead of the conventional quenching method of water quenching to obtain an amorphous/nanocrystalline structure with Cu10Zr7 phase uniformly distributed around 70 nm in the amorphous matrix.The fracture strength is increased by about 17%from 1855 MPa in the as-cast state to 2170 MPa,and the plastic strain is also increased from 0%in the as-cast state to 1.2%.The TEM analysis of the step annealing process sample found that the amorphous alloy has a structural relaxation phenomenon when annealed below the glass transition temperature.After the annealing time is extended to 4 h,the atomic arrangement changes from the disorder of the high Gibbs free energy.The transformation of the arrangement to a low-energy ordered lattice.After step annealing of amorphous alloys,atoms grow along the ordered lattice produced by the structural relaxation phenomenon,and there is a coherent growth phenomenon between the precipitated phase and the ordered lattice produced by the structural relaxation,and finally the precipitated phase is formed.The distance between the intermediate crystal plane is reduced,and the atomic arrangement is more dense.