稀土Y对铸态ZK30镁合金高温塑性流变行为的影响

Effects of Rare-earth Y Doping on the High-temperature Plastic FlowBehavior of As-cast ZK30 Magnesium Alloy

摘要:

为了研究稀土钇(Y)对铸态ZK30镁合金高温塑性变形行为的影响,在变形温度为573~723 K、应变速率为0.001~1s_-1条件下,通过Gleeble热力模拟试验机对其进行了一系列恒温压缩实验,结合组织观察,研究了Y添加1.5wt%时对合金组织结构、流变行为、本构参数及高温塑性变形行为的影响。研究显示,Y细化了铸态合金晶粒,三角晶界处共晶产物明显增多、并演变为清晰的块状、网状结构；Y未对合金流变应力曲线的特征产生显著影响,但引起流变应力水平、峰值应力普遍增大。根据双曲正弦函数,线性拟合确定了Y添加前后合金的本构参数,建立了定量描述流变应力同变形温度和应变速率之间关系的本构方程,其中Y使应力指数(n=5.778)、表观变形激活能(Q=181.082)的平均值增幅超过14.2%和21.6%,表明Y导致合金塑性变形抗力增大。另外,高温压缩后的组织显示,Y有利于促使合金发生动态再结晶,晶界处再结晶晶粒增多、晶粒尺寸更细小,表明含稀土Y第二相影响了晶界界面迁移。

Abstract:

In order to improve the understanding of the effectSmechanism of rare earth yttrium (Y) element on the plastic deformation of as-cast ZK30 magnesium alloy, and to use it more effectively, carried out a series of isothermal compressive tests of specimens were performed in the deformation temperature range of 573~723 K, and the strain rate range of 0.001~1 s_-1 on thermo-mechanical simulator. Combing with the microstructure observation, the effects of Y (1.5wt %) on the microstructure, flow behavior, constitutive parameters and high temperature plastic properties of the ZK30 magnesium alloy were investigated. According to the hyperbolic function, constitutive parameters of the alloy were obtained by linear fitting, a nonlinear flow model and its constitutive equation have been established and employed for studying the plastic deformation behavior and the relationship between temperature, strain rate and flow stress. The results showed that Y could refine the as-cast grain and increase the amount of eutectic intermetallic compound in grain boundaries. The Y doping could effectively enhance the flow stress level and peak stress, but the change trend of true stress-strain curves are less affected. The average activation energy (Q=181.082KJ.mol_-1) and stressSexponent (n=5.778) for the plastic deformation have been determinded, enlarged by 14.2% and 21.6%, respectively. The resultsSshow that theSplastic deformationSresistanceSof theSalloySis enhanced. Combined with metallurgy microstructure of these samples after deformation, Y could refine the grain and increase the amount of the dynamic recrystallization in triangle boundaries. The results showed that Y was facilitatingSdynamicSrecrystallization occur, and it was influencing theSmechanism of interface migration.