大挤压比制备高强Mg-Gd-Y-Zn-Zr合金的显微组织及强韧化机理

通过大挤压比热挤压工艺制备出含有长周期堆垛有序(LPSO)相的高强塑性Mg-8.34Gd-2.32Y-1.04Zn-0.07Zr合金。通过金相显微镜、EBSD、TEM等显微检测方法及数学模型研究了合金显微组织与力学性能之间的关系。结果表明,合金经热挤压后形成了双峰结构,在时效处理后同时存在14H-LPSO相和β′析出相。合金获得了较好的力学性能,抗拉强度、屈服强度和伸长率分别达到463.1 MPa,392.6 MPa和13.3%。合金屈服强度以细晶强化、析出强化和固溶强化的贡献为主。高占比的细小再结晶晶粒、弱织构以及LPSO相的存在对合金塑性的提升有重要作用。

Modeling the Dynamic Recrystallization of Mg–11Gd–4Y–2Zn–0.4Zr Alloy Considering Non-uniform Deformation and LPSO Kinking During Hot Compression

Hot compression tests of Mg–11 Gd–4 Y–2 Zn–0.4 Zr alloy(GWZK114)were conducted at a deformation temperature range of 300–500°C and a strain rate range of 0.01–10.0 s-1.Based on systematic microstructure observation,it is confirmed that long period stacking ordered(LPSO)phase displays essential and evolving roles on the dynamic recrystallization(DRX)behavior.The results indicate that the plastic deformation is mainly coordinated by simultaneous exist of LPSO kinking of lamella 14 H-LPSO phase and DRX at 350–450℃,and DRX at 500℃.Further,it is found that the LPSO kinking induced during 350–450℃can delay the DRX.A phenomenological DRX model of GWZK114 alloy is established to be XDRX=1.exp[-0.5((ε-εc)/ε^*)0.91].Non-uniform distribution of plastic strain during compression was considered via finite element method and it ensures a good prediction of DRX fraction under a large plastic strain.Meanwhile,an enhanced DRX model,taking its formulation as XDRX={1.exp[-0.5((ε-εc)/ε*)0.91]}(T/(226.8)-1)n,n=3.82ε0.083,is proposed for the first time to capture the hindering effect of 14 H-LPSO kinking on DRX behavior.The predicted results of this enhanced DRX model agree well with the experimental cases,where 14 H-LPSO kinking is dominated or partially involved(300–450℃).Besides,a size model of DRX grains is also established and can depict the evolution of DRX grain size for all the investigated compression conditions with accounting for temperature rising at high strain rates(5 s^-1 and 10 s^-1).

Mg-Y-Zn合金高应变率下LPSO结构的变形机制

长周期堆垛有序(long period stacking ordered,LPSO)结构是广泛存在于Mg-Y-Zn系镁合金中一种强化相。本文利用分离式霍普金森压杆(SHPB)和万能试验机测试了Mg-Y-Zn变形镁合金的动态压缩力学性能和准静态压缩力学性能,结果显示,Mg-Y-Zn变形镁合金存在一定的应变率强化效应;利用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射仪(XRD)分析实验材料的微观组织,通过比较LPSO结构在高应变率和准静态应变率下的变形机制,研究LPSO结构对材料应变率强化效应的作用:Mg-Y-Zn合金中有大量层状的LPSO结构在基体上随机分布;准静态条件下,在变形后的LPSO结构中发现类位错,LPSO结构主要的变形方式是启动基面滑移系;动态条件下,变形后的LPSO结构中存在大量位于基面上的类位错和少量位于柱面上的类位错以及位于锥面上的类位错,启动了临界切分应力更大的滑移系,LPSO结构的变形方式是层状结构厚度变薄,发生了聚集、扭折和断裂;LPSO结构附近的基体在变形过程产生了大量的位错缠结,产生大量的亚晶。

Hot Deformation and Work Hardening Behavior of an Extruded Mg–Zn–Mn–Y Alloy

The aim of this study was to evaluate the strain hardening and hot deformation behavior of asextruded Mg-Zn-Mn （ZM31） magnesium alloy with varying Y contents （0.3, 3.2, and 6 wt%） via compression testing along the extrusion direction at room temperature, 200℃ and 300 ℃. Texture and phases were identified by X-ray diffraction. Alloy ZM31 ＋ 0.3Y consisted of a mixture of fine equiaxed grains and elon- gated grains with 1-phase （Mg3YZno）; alloy ZM31 ＋ 3.2Y contained 1-phase and W-phase （Mg3Y2Zn3）; alloy ZM31 ＋ 6Y had long-period stacking-ordered （LPSO） X-phase （Mg12YZn） and Mg24Y5 particles. With increasing Y content the basal texture became weakened significantly. While alloys ZM31 ＋ 0.3Y and ZM31 ＋ 3.2Y exhibited a skewed true stress-true stain curve with a three-stage strain hardening feature caused by the occurrence of {1072} extension twinning, the true stress-true stain curve of alloy ZM31 ＋ 6Y was normal due to the dislocation slip during compression. With increasing temperature the extent of skewness decreased. While the compressive yield stress, ultimate compressive stress, strain hardening exponent, and hardening capacity all decreased as the temperature increased, the retention of the high- temperature deformation resistance increased with increasing Y content mainly due to the presence of thermally-stable LPSO X-ohase.