Effect of vibration amplitude at two different frequencies on the microstructure of Al A356 alloy processed via vibrated cooling slope abstract
Cooling slope casting is one the semisolid casting methods with a simpler technology as compared with other conventional semisolid casting processes. Nevertheless, this technique is a two-stage semisolid process requiring re-heating to semisolid region for gaining a globular structure. In the present study, a relatively new process, termed as Vibrating Cooling Slope (VCS), developed at university of Tehran utilized to gain a non-dendritic globular structure in A356 Al alloy. In this technique, the conventional cooling slope and vibration casting methods have been combined into an integrated one for producing globular structures in the as-cast condition. The effect of the vibration amplitude in the range of 120 to 800μm at two different vibration frequencies of 40 and 60 Hz on the morphology of specimens examined. The microstructure of the sample produced at the amplitude of 120 μm and frequency of 40 Hz was not globular but after reheating turned to globular. However, the sample produced by VCS at the amplitude of 120 μm and frequency of 60 Hz as well as the samples processed at the amplitude of 400μm and 800μm at both frequencies of 40 Hz and 60 Hz exhibited a globular structure in the as-cast condition. In addition, increasing the vibration amplitude from 120 to 800μm resulted in decreased size of globules for both applied frequencies. Also, the shape factor of globules increased with increasing the amplitude of vibration in the range of 120 to 400 μm, but remained almost constant for further increase of this parameter. The increased vibration frequency resulted in a smaller globule size and a larger shape factor for all of the explored amplitudes. The microstructural analysis revealed that the optimum microstructure (from the point of view of the size and morphology of globules) achieved at the vibration amplitude of 800 μm and frequency of 60 Hz. These results attributed to increased amount of the shear stress imposed on the semisolid alloy on the cooling slope by increased amplitude and frequency of the applied vibration