控制浇注法制备半固态坯料的研究

The Study of Semisolid Feedstock Formation by Controlled Pouring

针对半固态成形中需要具有细小颗粒均匀分布的非枝晶坯料以获得流变特性,采用控制形核的方法,制备了具有触变特性的半固态坯料.亚共晶Al—Si合金以不同的浇注温度浇注到永久模中,随着浇注温度的增加,晶粒尺寸和形状成柱状晶的趋势增加.带有金属丝网的试验表明,低温浇注时型壁形核机理起重要作用.675℃以下浇注时,型壁形核的生存率决定了最终结构, 包括晶粒尺寸和形貌;浇注温度高于675℃时,其他的形核机理起决定作用.

Semisolid metal forming requires feedstock material with a fine - grained, no - dendritic structure to a-chieve thixotropic properties. In this study, a Controlled Nucleation method was used for the formation of thixotropic structures. Hypoeutectic Al - Si alloy was cast into a permanent mould using different pouring temperatures. As the pouring temperature increased, the grain size increased and the tendency to form columnar grains also increased. Gauze experiments show that the mechanism of the 'wall crystals' plays a very important role at low pouring temperatures. The survival rate of the wall crystals determines the final thixotropic structure including both grain size and morphology up to 675 ℃ pouring temperature, while other nucleation mechanisms might operate at higher temperatures.