Study On Die Casting Of Zr Based Bulk Amorphous Alloy Gear

Because of its unique structure,amorphous alloy has many excellent properties,such as high strength,high hardness and corrosion resistance,so it has been used in many fields.However,amorphous alloys are seldom used as structural parts and their size is relatively small.As a forming process,vacuum pressure casting has many advantages,such as high cooling rate and near net forming.However,there are few reports about vacuum die casting of amorphous alloys.Therefore,in this paper,zirconium based bulk amorphous alloy was selected as the raw material to carry out the research on the die casting of larger castings,and to explore the appropriate process methods,in order to obtain the castings with complete shape and clear outline and meet the requirements of structural performance,so as to provide beneficial technical reference for the casting and application of amorphous alloy.This article chooses Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 system as master alloy material,vacuum die casting process method is adopted to improve the shape.Under the conditions of mold temperature of 363 K,393 K,413 K and casting temperature of 1193 K,1243 K,1293 K,1343 K,the casting process of zirconium base bulk amorphous alloy was studied,and the gear castings with outer diameter of 37mm and number of teeth of 35 were successfully die-cast.The effects of die-casting process parameters on microstructure,thermal stability and mechanical properties of amorphous alloy gear were studied by X-ray diffractometer,differential scanning calorimetry,mechanical properties test equipment and SEM.According to the results of XRD experiment,under the conditions of vacuum degree of 25 Pa,casting temperature of 1343 K,mold temperature of 363 K,393 K and 413 K,the gear casting is completely amorphous.The gear casting has good filling,complete casting shape and clear outline.Under the conditions of vacuum degree of 50 Pa,casting temperature of 1393 K and mold temperature of 363 K,although the gear casting is still completely amorphous,it can be found that there are porosity defects between individual teeth of the gear casting.The results of DSC experiment show that different process conditions have a significant effect on the thermal properties of castings.For the gear casting with casting temperature of 1343 K and mold temperature of 363 K,the related thermal physical parameters(T_g,T_x,T_p1,T_p2 and T_p3)are larger.Crystallization kinetics study shows that the casting stability is better when the mold temperature is 363 K and the casting temperature is 1343 K.The mechanical properties of gear castings were characterized by Rockwell hardness and compression test at room temperature.The experimental results show that different process conditions have little effect on the surface hardness of gear castings,which are in the range of HRC 52.3-53.5.When the casting temperature is 1343 K and the die temperature is 363 K,the gear casting is amorphous structure.The compression specimen has good mechanical properties and its fracture strength is 1887 MPa.Casting compression deformation of the specimen under different process conditions are brittle fracture,the fracture morphology was observed by scanning electron microscope,found the suction casting method of the preparation of as-cast sample only smooth area,the fracture morphology of the veins of the distribution of the typical shape of decorative pattern,and different compression fracture process under the condition of gear casting with smooth areas and uneven area,The smooth area has uneven vein pattern,and the fracture morphology of die-casting samples has typical brittle fracture characteristics.