Al-Zn-Mg-Cu-Zr合金的热变形行为研究

Hot Deformation Behavior of Al-Zn-Mg-Cu-Zr Alloy

以7000系Al-Zn-Mg-Cu-Zr合金为研究材料,在Gleeble1500热模拟试验机上进行变形温度250~400℃,应变速率0.01~10 s^(-1)条件下的等温压缩试验。研究结果表明:合金在等温压缩过程中的流变应力随着应变速率的增大而增大,随着变形温度的增大而减小。当应变速率为10 s^(-1),变形温度为250℃时,合金的峰值应力可达205 MPa。大部分的真应力-应变曲线呈现动态再结晶特征,结合TEM分析,动态再结晶的形成机制是位错通过滑移和攀移逐渐演变成小角度晶界(2°~15°)和大角度晶界(>15°),依靠位错重排在原始晶粒内部形成亚结构,最终形成完整晶界。同时,采用Arrhenius模型和Zener-Hollomon参数方程,构建了Al-Zn-MgCu-Zr合金的本构方程,其中合金的平均变形激活能为324 187 J/mol。此外,通过Prasad失稳判据等模型,构建了0.2、0.4以及0.6应变下的Al-Zn-Mg-Cu-Zr合金的热加工图,获得可加工窗口为:252~400℃,0.01~0.015 s^(-1)。

7000 series Al-Zn-Mg Cu Zr alloy was selected as the research materials,and isothermal temperature compression tests were conducted on Gleeble1500 thermal simulation testing machine at deformation temperatures of 250-400℃and strain rates of 0.01-10 s^(-1).The research results indicate that the flow stress of the alloy increases with the increase of strain rate and decreases with the increase of deformation temperature-1 during isothermal compression.When the strain rate was 10 s and the deformation temperature was 250℃,the peak stress of the alloy could reach 205 MPa.Most of the true stress–strain curve exhibited the characteristics of dynamic recrystallization.Combined with TEM analysis,the forming mechanism of dynamic recrystallization was that the dislocations gradually evolve into low angle grain boundaries(2°-15°)and large angle grain boundaries(>15°)through sliding and climbing,and relying on dislocation rearrangement to form a substructure inside the original grain.Finally,a complete grain boundary formed.The constitutive equation of Al-Zn-Mg-Cu-Zr alloy was constructed by using arrhenius model and zener hollomon parametric equation,in which the average deformation activation energy of the alloy was 324187 J/mol.In addition,hot working diagrams of Al-Zn-Mg-Cu-Zr alloy under 0.2,0.4 and 0.6 strains were constructed by Prasad instability criterion and other models,and the machinability windows were 252-400℃,0.01-0.015 s^(-1).