单β相镁锂合金Mg-11Li-3Al-0.4Y中温拉伸行为

Tensile behavior of β-phase Mg-11Li-3Al-0.4Y alloy at medium temperature

采用熔铸、大变形轧制及退火等工艺制备厚度为1 mm的Mg-11Li-3Al-0.4Y合金板材,结合扫描电子显微镜、高温拉伸试验机等实验方法,研究合金在温度范围为50~200℃和应变速率范围为0.001~0.1 s-1的中温变形行为、再结晶行为和组织性能。在Arrhenius双曲正弦型方程的基础上构建适用于单β相含稀土镁锂合金的塑性变形本构方程。研究结果表明:对于单β相Mg-11Li-3Al-0.4Y合金,流变应力随变形温度的升高和应变速率的降低而降低,且真应力-真应变曲线中的锯齿波符合动态应变时效中的Portevin-Le Chatelier效应,这是首次在单β相Mg-Li-Al合金中观察到Portevin-Le Chatelier效应。结合断口分析,发现热轧合金板材在中温拉伸过程中,随着温度的升高,合金拉伸断裂方式由较低温度时的准解理断裂转变为较高温度下的韧窝断裂。

New β-phase Mg-11Li-3Al-0.4Y alloy sheet with thickness of 1 mm was prepared by casting, hot-rolling and annealing processes. The fracture morphology and mechanical properties were investigated with scanning electron microscope and medium-temperature stretch test machine, respectively. Additionally, constitutive equation including flow stress, strain rate and deformation temperature was established by hyperbolic sine model with Zene？Hollomon parameter. The results show that the flow stress decreases with the increase of deformation temperature and reduction of strain rate. A pronounced post-relaxation effect followed by a serrated flow curve is shown in true stress-strain curves with low strain rate, which is also called the Portevin？Le Chatelier effect, and it is the first time that Portevin？Le Chatelier effect appears in β-phase Mg-Li-Al alloy. Cleavage fracture is replaced by dimple fracture with the increase of deformation temperature, according to the observation of electron microscope.