应变速率和温度对Mg-1Y挤压板材拉伸变形行为的影响

Effects of Strain Rate and Temperature on The Tensile Deformation Behavior of An Extruded Mg-1Y Sheet

摘要:

在温度为25至300 ℃ 应变速率为0.001至0.1 s-1的范围内研究了 Mg-1Y (wt.%) 挤压板材的拉伸变形行为。在0.1 s-1的应变速率下，当温度从室温增加至300 ℃时抗拉强度从247.9 ± 5.8 MPa降低了49.3 %。本文研究的板材即使在室温下也表现出了明显的应变速率敏感性。室温下当应变速率从0.1 s-1降低至0.001 s-1，抗拉强度降低11.8 %。在室温和250 ℃温度范围内可以通过Garofalo双曲正弦本构方程来描述合金的流变行为。测得的应力指数n为27.8 ± 8.9，激活能Q为124.6 ± 6.1 kJ/mol，Q值意味着变形是位错攀移控制。在中间温度（ ~ 150 – 250 ℃）时板材表现出锯齿流变行为，这种现象在较低应变速率更明显。同时断裂延伸率随着温度升高而反常地降低。认为上述两种变形特征和Y原子和位错的强烈的相互作用有关系，这种作用即为动态应变时效（DSA）。应变速率敏感因子（m）随温度增加而增加。在300 ℃下m从0.068增加至0.11，说明Y元素的添加可以激活更多滑移系。变性后显微组织的观察表明孪晶被温度抑制，同时与增加的m相一致。300 ℃下观察到有动态再结晶（DRX）的出现，应变速率越低DRX越明显。

Abstract:

The tensile deformation behavior of an extruded Mg-1Y (wt.%) sheet was investigated in the temperature range of 25 (RT) to 300 ℃ and at strain rates from 0.001 to 0.1 s-1. Ultimate tensile strength (UTS) decreased by 49.3% from 247.9 ± 5.8 MPa when temperature increased from RT to 300 ℃ at the strain rate of 0.1 s-1. It is interesting to note that the flow behavior of the studied sheet exhibited pronounced strain rate sensitivity even at RT. The UTS at RT decreased by 11.8% as the strain rate decrease from 0.1 s-1 to 0.001 s-1. The flow behavior of the alloy can be described by the Garofalo hyperbolic sine constitutive equation in the temperature range of RT to 250 ℃. The measured stress exponent n was 27.8 ± 8.9, and the activation energy Q was 124.6 ± 6.1 kJ/mol. The Q value implied that deformation was controlled by dislocation climb. At intermediate temperature range (~ 150 - 250 ℃), the sheet exhibited serrated flow behavior, and this phenomenon was pronounced at lower strain rates. Simultaneously, the elongation to failure (EL) decreased anomalously with increasing temperature. The above two deformation features were believed to be closely related to the strong interaction between Y solute atoms and dislocations which is known as dynamic strain aging (DSA). The value of strain rate sensitivity ( m ) increased with increasing temperature. The m increasing from 0.068 to 0.11 at 300 ℃ indicated that the addition of Y resulted in the activation of more slip systems. The deformation microstructure observation revealed that twinning was depressed with temperature, which was consistent with the remarkably increased m values. Dynamic recrystallization (DRX) was observed at 300 ℃, and it was promoted with lower strain rate.