液固温区A356合金瞬态流变行为的研究

STUDY ON TRANSIENT RHEOLOGICAL BEHAVIOR OF SEMI-SOLID A356 ALLOY

采用自行研制的流变装置进行瞬态流变试验,研究了切应变速率突变对液固温区不同初生α相形态A356合金瞬态流变行为的影响规律。初生α相形态是以切应变速率为141.8s-1的等温剪切获得的不同程度的退化枝晶。研究表明,等温剪切过程将使半固态合金的初生α相逐渐退化,表现为表观粘度逐渐降低直至达到平衡态。对试验结果进行回归分析,得出表观粘度与时间的瞬态流变经验方程,以及方程参数与半固态合金初生α相形态和切应变速率之间的关系。由研究结果可知,随着初生α相形态由发达枝晶向球状晶变化,半固态合金剪切稀释或伪塑性越显著,同时对时间具有更加强烈的依从性,从而具有更明显的触变性。

The influence of abrupt shearing on transient rheological behavior of semi-solid A356 alloy with different morphology of primary a-phases is explored through the use of rest time experiment by a self-designed rheometer. The morphology of primary a-phases is degenerated dendrites prepared via isothermal mechanical stirring at 141.8 s-1. Results indicate that the primaryα-phases are gradually degenerated under isothermal shearing, as a result, the apparent viscosity of semisolid A356 alloy is gradually reduce to a equilibrium state. Empirical transient rheological equations are then obtained by ways of curves fitting. The relation between parameters of the empirical equation and morphology of primaryα-phases of semisolid alloy is also gained by means of regression analysis. Results also show that the semisolid A356 alloy exhibited more notable shear thinning or pseudoplastic behavior, and expressed more prominent behavior of time dependence along with the degeneration of primary a-phases of the semisolid alloy, in other words, the semisolid alloy is possessed by obvious thixotropic behavior.