| The nucleation of metal materials is generally associated with subcooling.A certain degree of undercooling requires that the mold material has a good heat transfer performance.However,due to the existence of gas entrapment phenomenon,so that the metal liquid and mold wall mixed with a part of the air,resulting in deterioration of the heat transfer performance of metal,while the metal heterogeneous nucleation affected.The existence of gas entrainment is mainly due to the existence of a certain degree of micro-roughness of the mold surface,when the metal liquid and the mold surface contact,the groove part is sealed air,the formation of the Cassie wetting model described the phenomenon.This phenomenon hinders the contact of the molten metal with the mold surface and reduces the heat transfer efficiency to the outside during the cooling of the molten meta.At the same time,this kind of metal liquid and mold wall from the formation of wetting system,it can be found that the wetting of metal nuclei play a pivotal role.In this paper,the heterogeneous nucleation of metal as the starting point,combined with Young's equation,model theory and model theory,the main study is the metal surface wetting.The first part of the experiment mainly uses pure aluminum and high-purity aluminum materials which are easy to prepare samples,the hydrophilic aluminum and high-purity aluminum surface are prepared by chemical etching,the change rule of wettability with aging time was analyzed at room temperature for aging.The samples were etched with the concentration of hydrochloric acid,the samples were etched for 4min to20 min,cleaned and dried.The prepared samples were measured with OCA15 EC contact angle measuring instrument.The samples were then allowed to stand at room temperature,and the wetting angle after aging was recorded.The change of the wetting angle was analyzed.The microscopic morphology of the surface of the specimen was observed by scanning electron microscopy.The reason of the change of the wetting angle was analyzed by Wenzel theory and Cassie theory.EDS analysis of aging after the sample contains the content of elements of the changes in the mechanism of wetting changes.The second part of the prepared samples in the high temperature furnace 200?,300? and 400? high temperature aging,aging time are 1h,recorded before and after the wetting angle.Observe the microstructure of the sample surface,analyze the change of the element in the EDS,explain the mechanism of the change of the wettability.The results show that the wetting angle of the samples prepared by different etching time is different.The pure aluminum can obtain a stable surface morphology.The high purity aluminum material can bestabilized for 12 minutes.Wetness,the sample wetting angle maintained at 12° below,and the morphology is better.After the high temperature aging,it was found that the wetting angle of the sample prepared by different etching time was different,and the wetting angle increased rapidly at 1 h after 200?high temperature.The wetting angle began to become smaller at 1h after 300? aging,the sample becomes super-hydrophilic after 400? aging.In order to make the research more fully,the hydrophilic surface was prepared on the 304 stainless steel with strong corrosion resistance by chemical etching method.Therefore,the third part was treated with 304 stainless steel as the base material and chemical etching as the preparation method.The change of wetting angle after room temperature aging and the wetting angle after high temperature aging are similar to those of aluminum-based materials,however,due to the different elements of different hydrophilicity between the metal,there are some differences between the two metals.Therefore,this paper is important for guiding the wettability during the solidification of molten metal. |
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