Plastic Flow Characteristics of an Extruded Mg-Li-Zn-RE Alloy

摘要:

利用热机械模拟方法详细研究了一种挤压Mg-7.8Li-4.6Zn-0.96Ce-0.85Y-0.30Zr合金的流变行为，温度范围为250~450 °C，应变速率在0.001~10 s-1之间。结果表明，该合金的流变应力-应变曲线表现为流变应力先逐渐增加到一个最大值，而后软化。这种流变行为表明在典型的热加工过程中伴随着动态再结晶。该合金的流变应力曲线可以用整个变形温度范围内的双曲正弦函数来拟合。幂指数方程和指数方程并不能很好地拟合应力曲线。双曲正弦方程中的应力指数n很高，而且随着变形温度的增高而逐渐增加。合金的热变形过程主要被位错的攀移所控制。合金的平均热变形激活能Q为148 kJ/mol，高于Mg的自扩散激活能(135 kJ/mol)和点阵扩散激活能(103 kJ/mol)。以上讨论的结果可以归因于合金中稀土元素的加入

Abstract:

The flow behavior of an extruded Mg-7.8Li-4.6Zn-0.96Ce-0.85Y-0.30Zr alloy was investigated by a thermo-mechanical simulator in the temperature range from 250 to 450 °C and the strain rate range from 0.001 to 10 s-1. The results indicate that the flow stress-strain curves of the alloy are characterized by an increase of the flow stress until a maximum stress value followed by the flow softening being observed. Such flow behavior is a characteristic for hot working accompanied by dynamic recrystallization. The flow behavior of the alloy can be represented by a hyperbolic sine type equation during the whole deformation temperature; however, it is not proper to fit the flow stress equation using the power and the exponential equation. The stress exponent n in the hyperbolic sine equation is high and increases with increasing of deformation temperature. The hot deformation process of the alloy is mainly controlled by dislocation climb. The average hot deformation activation energy Q of the alloy is 148 kJ/mol, which is higher than both the self-diffusion activation energy of Mg (135 kJ/mol) and the lattice diffusion activation energy of β-phase (103 kJ/mol). The results discussed above can be attributed to the addition of rare-earth (RE)