Study And Application Of Interfacial Heat Transfer Between Metal Melt And Substrate

Compared with rapid solidification method,near rapid solidification method has relatively small cooling rate and wider development prospect in industry,thus attracts much researchers'attention.Nowadays metal substrate with high thermal conductivity is widely used to produce products with small size in near rapid solidification process.The property of product is highly relying on interfacial heat transfer.In this paper,we analyze the heat transfer mechanisms during interfacial solidification process.The character of higher heat flux and cooling rate during liquid-solid contact in interface during solidification is exploited.Fusible metal mold casting method,which is a novel near rapid solidification method is put forward.To illustrate the feasibility of fusible metal mold method,firstly melting droplet experiment is designed to analyze the interfacial heat transfer during metal contact with substrate.T-type thermocouple is adopted and integrated with substrate to improve resolution.Heat transfer coefficient development in 20ms after melt drop is studied,melt materials include Al-Cu,Al-Si,Al-Mg and Al-Zn alloy.At least three experiments is conducted each group to improve reliability.Results show that maximum heat transfer coefficient is acquired instantaneously after melt contacts substrate,and then decreases gradually.Evolution of heat transfer coefficient can be expressed as?=₁·^-8)by approximation.Al-30wt.%Cu has relatively higher instantaneous heat transfer coefficient compared with other materials studied?Secondly,304 stainless steel is chosen to making small size ingot.Fluent software is used to establish simplified model to stimulate liquid fraction and temperature field distribution during solidification of 304stainless steel in fusible metal mold.Results show that fusible metal mold starts to melt at 12.8s after filling and melts completely at 40s,when the fusible metal mold begins to melt,a thin solidified layer has formed.The ingot solidifies completely at 140s and the fusible metal mold keeps liquid all the time until 1240s.Finally,M2 high speed steel is selected as experiment material and made ingot with tiny size.M2 high speed steel is often used as cutting tools.Typical as-cast structure of M2 high speed steel consists of dendrites surrounded by continuous inter-dendritic network of eutectic carbides.High speed steel has poor thermal conductivity and the carbides are coarse,which is harmful to the property of high speed steel.By comparison experiments,fusible metal mold method can improve cooling rate by100%.Carbides are refined and present complex irregular laminar morphology.Line scanning analysis reveals that little aluminum element is penetrated into the ingot,about 250?m deep.This thin layer can be removed by later manufacturing process,thus has little influence on the original ingot.