A Study On Friction Mechanism Of Micro Plastic Forming For Bulk Amorphous Alloys

In this work, a copper mold casting method was used to produce Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloys. The structure and properties of material were investigated by method of X-ray diffraction(XRD). The present paper developed the stretched exponential function and used the constitutive equation into finite element software for the Finite element (FE) simulation of the micro plastic forming in supercooled liquid region(SCL) of Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloys, then the friction factor calibration curves(cup height ratio versus stroke) was established. The double cup extrusion test(DCET) was carried out by Zwick/Roell mechanical property testing system, the size of upper cup and lower cup were measured by the 3D video microscope system. Finally, by matching the cup height ratio and punch stroke obtained from experiments to the friction factor calibration cruves, the friction factor of the micro plastic forming in supercooled liquid region can be obtained.The plastic forming was carried out under different deformation temperature of 415℃,430℃,445℃,460℃and different strain rates of 5×10-4s^-1, 1×10-3s^-1, 5×10-3s^-1,1×10-2s^-1. The influence on friction factor of extrusion stroke was also investigated under the condition of fixed deformation temperature and strain rate. It has been found that the friction factor is significantly affected by both deformaiton temperature and strain rate. In addition, the extrusion stroke also affects the friction factor. When the deformation temperature is ranging form 445℃⁴60℃and the strain rates are ranging form 5×10-3s^-11×10-2s^-1, the friction factor is varied form 0.23 to 0.28. But when the deformation temperature is ranging form 415℃⁴30℃and the strain rates are unchanged, the friction factor is varied form 0.6 to 0.66. Furthermore, a four-step period of change of friction factor is exhibited when the extrusion stroke increases. The friction factor increases form a stable platform which is showed in the beginning of extrusion stroke, then it decreases with the increase of stroke, and finally another stable platform is presented. The aim of the present article is to find the friction mechanism of micro plastic forming of Zr55Al10Ni5Cu30 bulk amorphous alloys, tribology is used to explain the results of experiments. The conclusions are meaningful to microforming processing and FE simulation.