| "Gasar" is also defined unidirectional solidification of metal-gas eutectic, at the same time it is also considered as a revolutionary method of producing porous metals. The porous structure is called as "Gasarite" meaning the cylindrical pores are aligned regularly in the solidification direction. Compared with conventional sintered or frothed porous materials, Gasar ordered porous metal has the same property many advantages such as lower density, high specific strength, high energy absorbing ability, fine acoustics performance and electromagnetic shielding characteristic. In addition, porous metal perform some particular properties such as high mechanical property, thermology property, electricity and the capability of penetration, all of these properties are related to the porosity of material. Thus, porosity is an important structural parameter. The relationship between porosity and preparation process should be studied well because we can control the lotus porous structural metal quantitatively through adjusting process parameters, and consequently the excellent performance lotus-type porous material can be obtained.Lotus-type porous copper materials fabricated by the method of unidirectional solidification of metal-gas eutectic are researched systematically in this paper. Order porous copper materials with various pore structures were prepared successfully by using continuous casting technique and mold casting technique in the Gasar apparatus which designed by our laboratory. Heat transfer model was established in Gasar solidification through assuming heat transfer model of unidirectional solidification in continuous casting technique. The pore model was also derived from Gasar solidification in porous materials. Based on the solute mass conservation law and Gasar theory, unidirectional solidification Physicals model was built during solidification in porous metal.In addition, porosity model was constructed by considering solute escape and determining escape coefficient. As shown in the formula we can conclude that porosity is related to gas pressure and upside temperature, and have no concern with solidification rate during solidification.Theoretical values of porosity are in agreement with our experimental results by analyzing the variation of porosity under different hydrogen partial pressure and upside temperature in porous copper fabricated by continuous casting technique. Also, the variation of porosity was predicted when the argon was added. The reasons for the variation of porosity and the effect of upside temperature on the porosiry under different hydrogen and argon pressure are studied. Results show that porosity increases when the partial pressure of hydrogen increases for cases of no pressure of argon above melt at a certain temperature, while porosity first increases and then decreases as the partial pressure of hydrogen increases for case of nonzero pressure of argon above melt. At a certain temperature during continuous casting technique, porosity increases with increasing upside temperature, and it has the same trend when a certain amount of argon is added.The mode casting technique was improved based on continuous casting technique at a certain gas pressure. The derived porosity formula was also used to predict the porosity of mode casting technique, and the conclusion shows that the curves of porosity with gas pressure and upside temperature are in agreement with experimental results in mode casting technique. Compared with the continuous casting technique, the porosity in mode casting technique is less because escape coefficient increases under mode casting technique.The predicted theoretical porosity of lotus-type porous magnesium is in agreement with the data obtained by Tsinghua research group. Compared to the porous copper, the escape coefficient in porous magnesium is much less because escape coefficient is related to the solubility of hydrogen in melt, and the escape coefficient decreases with increasing solubility. |
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