Numerical Analysis And Experimental Research On Rheological Behaviour Of Semi-solid Melts

The semi-solid forming processes of metals technology combines the advantages of solidification forming and plastic forming.The quality of the produced parts is comparable to that of plastic formed parts,and the production cost is close to solidification forming.Therefore,it has broad application prospects in the field of automobile light weighting.The semi-solid metal melt prepared by special process has different rheological behaviors from liquid and solid,and which is a kind of non-Newtonian fluid with shear thinning characteristics.Apparent viscosity is an important indicator to measure the rheological properties of semisolid metal melts.The apparent viscosity of the semi-solid metal melt has an important guiding role and significance for its forming process at the same time.The coaxial double-tube rheometer is the most commonly used device for studying semi-solid melt rheology,but the measurement principle of this rheometer is derived from the Newtonian fluid assumption.And the error correction method used in the rheometer cannot meet the requirements of apparent viscosity measurement of semi-solid melt.In addition,the existing rheometers suitable for semi-solid melts are mostly built and designed by scientific research institutions,and the test methods and equipment structures have not yet formed a unified standard,resulting in a wide variety of apparent viscosity data of semisolid melts.The purpose of this paper is to study the influence of the shape parameters of the coaxial double-tube rheometer and the flow state of the slurry in the measurement system on the measurement accuracy of the apparent viscosity of the semi-solid melt with the shear thinning characteristic.Correction of apparent viscosity measurement error is given based on this work.The research results of this paper will guide the design of the high temperature rheometer suitable for semi-solid melt apparent viscosity measurement and the formulation of the apparent viscosity measurement method.The work that has been done is as follows:?1?ANSYS Fluent was used to quantitatively analyze the end face effect error of the coaxial double-tube rheometer in measuring the apparent viscosity of semi-solid melt,and found that the error caused by the end face effect during the apparent viscosity measurement of shear thinning fluid is an important part of the apparent viscosity measurement error.Because the average shear rate of the end face of the inner cylinder is much smaller than that of the inner and outer cylinder gaps,the viscosity of the fluid near the end face is much larger than that in the gap.Using theoretical derivation,simulation numerical analysis combined with Al₂O₃ suspension apparent viscosity test experiment,a method is proposed to correct end face effect error by defining the average inner cylinder additional height ???.??? is obtained by fitting the linear relationship between the inner cylinder torque M and the immersion depth h.?2?The influence of rheometer shape parameters such as inner and outer cylinder radius ratio?,inner cylinder immersion depth h,bottom surface distance H,inner and outer cylinder gap ? and inner cylinder end face shape on apparent viscosity measurement accuracy was studied using ANSYS Fluent.Some conclusions obtained from the simulation were verified by the apparent viscosity test of Al2O3 suspension.?3?This paper studies the influence of the flow state of the fluid in the measurement system on the measurement accuracy of the apparent viscosity was studied.According to the characteristics of the rotating Couette flow,the influence of the apparent viscosity measurement accuracy of the Taylor vortex was quantitatively analyzed by ANSYS Fluent.Based on the study of Couette flow stability,an empirical formula for the limit speed of the inner cylinder to avoid Taylor vortex and end turbulence is given in this study.