Fundamental Studies On Mechanism Of Mechanical Vibration Improving Solidification Structure

Vibration solidification is a method of improving solidification structure by mechanical vibration. The effect had been confirmed by many experiments, but the mechanism was still in controversy. In this paper, a critical stress model considering the effect of "bending force" breaking dendrite was deduced in the condition of one-dimensional horizontal vibration based on the maximum tension-stress theory. A mechanism of the mechanical vibration improving the solidification structure was discussed that took the action of "bending force" as the major matter. On the basis of theoretical studies, apparatus for vibration solidification experiment were designed and fabricated. Simulation experiments using 30% NH₄Cl-H₂O solution and low melting-point metal solution were performed respectively.The simulation experiment using 30% NH₄Cl-H₂O solution was mainly investigated the influence of vibration parameters on the dendrite growth morphologies and the temperature variations in vibration solidification; the critical stress model of breaking dendrite was analyzed and simplified by the date of the specific dendrite obtained from the experiments. The influence of vibration frequencies on the drop in the liquid temperature, the growth rate of solidifying shell and the final solidification structure was studied mostly by using the low melting-point metal solution. The influences of superheat of liquid metal on vibration solidification were analyzed by comparing the final solidification morphologies at different superheat.The critical strength breaking dendrite in the condition of one-dimensional horizontal vibration was obtained from experiments, which could be expressed as relation between vibration parameters and dendrite sizes. The experiment results, including pictures and temperature-time curves, have revealed the existence of dendrite breaking. Because the resistance force upon the dendrite moving in liquid metal plays a determinant role, the critical stress model could then be simplified. The vibration frequency influences the growth rate of solidifying shell by affecting the growth of dendrite, and the length of broken dendrite and then growing rate of solidifying shell can be...