Study On Phase Change Heat Transfer In Semi-solid Alloy Solidification

The combination of semi-solid processing and casting technology, which was used in the preparation of magnesium alloy strip blank, not only had the characteristics of high efficiency, simple process, but also provided the slab with good processing properties.So it was very important for the development of semi-solid forming process and the improvement of processing quality on alloy strip to study the heat transfer mechanism of semi-solid phase change, to establish a suitable heat-transfer model of semi-solid slurry, to explore the relationship between the temperature field and the solid fraction, and to know the impact of process conditions on grain morphology.This article had a simple preliminary simulation on the heat transfer and flow behavior of semi-solid zinc alloy casting process.In order to get the phase diagrams under different temperature field,process measures we built a experimental platform about the heat transfer of semi-solid slurry to measure the temperature distribution of the alloy under different process.We dealed the Crystal phase with the image processing technology to calculate the solid fraction and the characteristic scales of grain shape.And we clarified the relationship between the solid fraction of semi-solid alloy and the temperature field to lay the foundation for the final order to investigate the relationship between the heat flow field and the evolution of grain structure interaction in the semi-solid forming process.Experimental results show that:1) The temperature values of alloy in the cylindrical barrel which was measured in high temperature differential conditions was lower than the one in low-temperature differential conditions.2) The temperature of semi-solid alloy leveled off under the measures of mechanical vibration and mechanical agitation.And during the cooling process, the temperature change gently without sharp decline.3) About the processing of the constitution diagram:in the metallographic method,We used the technology of "high-contrast black and white" into image processing to calculate the solid fraction, and obtained a clearer constitution diagram. the statistics derived from the solid fraction was similar with the calculated value, and the error was controlled within5%.4) Under the mechanical vibration or mechanical agitation,the constitution diagram showed that alloy grain become smaller, and the grain shape becomes more rounded with the dendrites reduction.Grain refinement was good for the improvement of mechanical properties of semi-solid alloy.