微合金含量Mg-Sn-Y合金的热变形行为及本构模型

Hot Compression Behavior and Constitutive Model of Dilute Mg-Sn-Y Alloy

少量热稳定性优异的第二相可作为Mg-Sn-Y合金体系中重要的强化相。为研究微量合金元素对Mg-Sn-Y合金热变形行为的影响,熔炼铸造了低合金含量的Mg-0.4Sn-0.5Y合金,采用热力模拟试验研究其热变形过程中流变应力应变行为,采用线性回归分析、金相分析(OM)、扫描电镜分析(SEM)等手段研究了该合金热压缩变形过程中的流变应力、变形温度和应变速率之间的关系,通过构建本构模型,结合显微组织演变分析变形激活等热变形行为。研究表明,Mg-0.4Sn-0.5Y合金在应变速率1×10^(-2)~1×10^(-4)s^(-1),变形温度300~450℃的热压缩变形情况下,流变应力应变曲线存在明显动态再结晶特征。流变应力、变形温度和应变速率三者之间关系满足Sellars和Tagert提出的双曲正弦形式修正的Arrhenius公式,满足流变应力本构方程·ε=1.555×10^(11)[sinh(0.0261σ)]^(3.665)exp[-183656.7/RT],合金变形激活能高于普通镁合金,分析其原因是基体中存在的及热变形过程中动态析出的弥散分布的颗粒状及针状的第二相粒子,阻碍了位错的交滑移和攀移,从而提高了位错开动所需的能量,造成了合金变形激活能的提高。

A small amount of the second phase with excellent thermal stability can be used as an important strengthening phase in Mg-Sn-Y alloy system.In order to study the influence of trace alloying elements on the hot deformation behavior of Mg-Sn-Y alloy,Mg-0.4Sn-0.5Y alloy with low alloy content was melted and cast in this paper.The flow stress-strain behavior of MG-0.4Sn-0.5Y alloy during hot deformation was studied by thermodynamic simulation test.Linear regression analysis,metallographic analysis(OM),scanning electron microscopy(SEM)and other methods were used to study the relationship between flow stress,deformation temperature and strain rate during the hot compression deformation of the alloy.The constitutive model was constructed to analyze the thermal deformation behaviors,such as deformation activation,combined with the microstructure evolution.The results show that the flow stress and strain curves of Mg-0.4Sn-0.5Y alloy have obvious dynamic recrystallization characteristics under hot compression deformation at strain rates of 1×10^(-2)-1×10^(-4)s^(-1)and deformation temperatures of 300~450℃.The relationship among flow stress,deformation temperature and strain rate satisfies the hyperbolic sinusoidal modified Arrhenius formula proposed by Sellars and Tagert.It satisfies the flow stress constitutive equation:·ε=1.555×10^(11)[sinh(0.0261σ)]^(3.665)exp[-183656.7/RT],and the deformation activation energy of the alloy is higher than that of the ordinary magnesium alloy.The reason is that there are diffusely-distributed particle second phases and more long rod and strip second phases in the matrix,which hinder the cross-slip and climbing of dislocations,thus increasing the energy required for dislocation initiation and resulting in the increase of the activation energy of alloy deformation.