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在讨论了关于改善颗粒被铝液的润湿性、微细颗粒在基体合金中均匀分散的原理的基础上,采用一套特别设计的装置,发展了一种在超声场中制备微细SiC、Si_3N_4和AlN颗粒增强MMC的办法。实验结果表明,高强超声处理大大地改善了铝液对微细颗粒的润湿性,使颗粒得以迅速混入熔体并均匀分散。MMC_p的铸态组织致密而均匀,表明设计的这套装置适于制备微细颗粒增强MMC_p。MMC_p可以像基体合金一样进行热挤压。微细颗粒的强化效果优于大颗粒,裂纹通常产生于大颗粒和金属基体间的界面上。 对高强超声在熔体中的传播及声空化和声流效应对微细颗粒的润湿和分散作用进行了实验观察和理论计算。结果显示,熔体中的声强足够高,导致了强烈的声空化和声流效应。声空化所引发的局部高压和高温分别为10~3～10~5大气压和10~3～10~4K。由于高强超声在熔体中迅速衰减,所以声空化最强作用区在变幅杆的端面。声流的最大速度达2.56m/s,熔体被其强烈搅拌。 运用力学及热力学观点分析了铝液润湿颗粒的机制。得出的结论是,超声对熔体/颗粒界面施加的能量极大地促进了铝液对颗粒的润湿。颗粒混入熔体的全过程包括润湿—弥散—部分脱附—少量团聚四个步骤。声空化引发的高压和高温可以清洗和活化颗粒的表面,使颗粒的表面能增大。而声空化引?
On the basis of discussing the principle of improving the wettability of particles by liquid aluminum and the fine particles dispersed uniformly in matrix alloy, a specially designed device was developed to fabricate a kind of ultrafine SiC, Si_3N_4 and AlN particle reinforced MMC approach. The experimental results show that the high-strength ultrasonic treatment greatly improves the wettability of the aluminum liquid to the fine particles, so that the particles can be rapidly mixed into the melt and uniformly dispersed. The as-cast microstructure of MMC_p was dense and uniform, which indicated that the designed device was suitable for preparation of fine particle reinforced MMC_p. MMC_p can be hot-pressed like a base alloy. The effect of fine particles is better than that of large particles. Cracks usually occur at the interface between large particles and metal matrix. The experimental observations and theoretical calculations of the wetting and dispersing effect of high-strength ultrasound in the melt and acoustic cavitation and acoustic flow on the fine particles were carried out. The results show that the sound intensity in the melt is sufficiently high, leading to a strong acoustic cavitation and acoustic streaming effect. Local high pressure and high temperature caused by acoustic cavitation are 10 ~ 3 ~ 10 ~ 5 atm and 10 ~ 3 ~ 10 ~ 4K, respectively. Due to the rapid decay of high-intensity ultrasound in the melt, the strongest area of acoustic cavitation is at the end of the horn. The maximum velocity of the acoustic flow reaches 2.56 m / s, and the melt is strongly stirred. The mechanics and thermodynamics are used to analyze the mechanism of aluminum liquid wetting particles. It is concluded that the energy applied by the ultrasound to the melt / particle interface greatly facilitates the wetting of the particles by the aluminum liquid. The whole process of mixing particles into the melt includes wetting - dispersing - partial desorption - a small amount of agglomeration in four steps. The high pressure and temperature induced by acoustic cavitation can clean and activate the surface of the particles, increasing the surface energy of the particles. The acoustic cavitation lead?