Study On Solidification Characteristics Of Alloys Based On High Speed Camera

The volume change behavior during solidification of the alloy will cause the shrinkage cavity and porosity in casting,which will have effect on the mechanical properties of the alloy.Therefore,studying the law of volume change during the solidification process has important practical value for controlling the casting defects and improving the quality of the casting.But due to the high temperature conditions before and after solidification,it has been difficult to accurately measure the volume changes caused by the alloy melt and solidification.This paper adopts two types of undercooled solidification technologies:vacuum electromagnetic levitation melting and glass cover technology,combined with high speed camera technology,computer aided image segmentation analysis technology,high-sensitivity temperature measurement technology and MATLAB program design technology,developed the volume change measurement method of before and after solidification.The volume variation and other solidification characteristics of Al-Si alloy suitable for levitation melting,Fe-B alloy and Co-B alloy not suitable for levitation melting were studied by the current method.The main results and conclusions obtained are as follows:?1?Based on the high-speed camera,several calculation methods for the sample volume change during levitation melting were designed:?a?boundary point ellipse fitting method;?b?gray threshold segmentation method;?c?local threshold segmentation method;?d?machine learning and dynamic threshold segmentation method.And MATLAB software programming was used to accurately calculate the volume change of the suspended Al-Si alloy samples with temperature before and after solidification.This method is suitable for the analysis of spherical samples.The calculation found that the volume change during solidification of Al-Si alloy at high temperature is expanding,and the volume expansion rate of solidification decreases with the increase of the undercooling.?2?Based on the volume measurement of the levitation melting alloy,the traditional deep undercooling technology for the purification of molten glass has been developed,that is,the measurement technology of the volume change before and after solidification of the alloy samples are difficult to suspend.This method is used to test the volume change of Fe-B alloy during solidification.The volume of the Fe-B alloy increases during the recalescence process,but the volume of overall solidification process shrinks,and the volume of the hypoeutectic alloy gradually decreases with the increase of the undercooling,and the volume of the hypereutectic alloy gradually increases with the increase of the undercooling.With the increase of the undercooling,the morphology of the solid-liquid interface changes from rough dendrite to smooth interface.?3?For the Co-B alloy,the interface of shape is rough under small undercooling,and it grows in multiple directions.When the undercooling is large,it grows in one direction and the interface is smooth and flat.With the increase of undercooling,the recalescence rate of the hypoeutectic and hypereutectic alloys of the same composition both increase,and the growth rate accelerates.When the undercooling is similar,the recalescence rate with the decrease of the B content.When the composition of the hypoeutectic alloy is constant,the interface movement rate increases with the increase of the undercooling.The closer to the eutectic composition,the faster the interface movement rate of the alloy.As the recalescence increases,the ratio of the recalescence time to the interface moving time tends to a constant.Comparing Co-B alloys with different compositions,it is found that the ratio of the interfacial migration rate to the recalescence rate gradually decreases with increasing undercooling.And the law is similar,and the ratio equation of interfacial migration rate and recalescence rate is derived.After solidification of the hypoeutectic alloy,the main product is?-Co phase.After solidification of the hypereutectic alloy,the main product is Co₃B phase.?4?By calculating the volume during the solidification process,the slope of the liquid volume is greater than that of the solid phase,regardless of the hypoeutectic or hypereutectic alloy.For the alloy with the same composition,the liquidus slope increases faster with the increase of the undercooling.In the change of the volume of the hypoeutectic alloy with the temperature,the slope of the liquid volume change is greater than that of the solid state,but the slope of the semi-solid state and the slope of the solid state is nearly parallel.For the hypereutectic alloy,the volume of the recalescence process increases,and then the volume of the solidification process continues to shrink.The entire volume decreases from the beginning to the end of solidification.The liquid phase region is larger than the solid phase region,and the slope of the liquid phase is higher than the slope of the solid phase.