Effects of initial microstructure on creep properties of Mg-8Gd-2Y-0.5Zr alloys
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摘要: 对不同初始组织形态（铸态、固溶处理态、T6处理态及挤压态）的Mg-8Gd-2Y-0.5Zr合金在200 ℃/70 MPa条件下进行100 h蠕变实验，探讨晶粒尺寸、铸态合金中初始第二相、时效析出相(β′相)对合金蠕变性能和蠕变机理的影响。结果表明：在相同蠕变条件下，时效态合金具有最佳的抗蠕变性能，挤压态合金的抗蠕变性能最低，在稳态蠕变阶段固溶态合金的蠕变性能稍高于铸态合金；晶粒尺寸细小是导致挤压态合金抗蠕变性能较低的主要因素；虽然在蠕变初期，铸态合金中初始第二相起到了蠕变强化作用，但晶内析出的大量与基体完全共格的β′相则是时效态合金以及固溶态合金具有较好抗蠕变性能的主要原因。
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关键词:
- 初始组织形态 /
- Mg-8Gd-2Y-0.5Zr合金 /
- 蠕变性能 /
- 析出相
Abstract: The present research investigated the creep properties of the Mg-8Gd-2Y-0.5Zr alloys with different microstructures (as-cast, as-solution, T6 and as-extruded) after creeping at 200 ℃/70 MPa for 100 hours. Effects of the microstructures, including grain size, Mg5(Gd, Y) phase in cast alloy, β′ phase on creep properties were studied. The as-extruded alloy shows the worst creep resistance due to the refined grains caused by dynamic recrystallization resulting from the extrusion process. Although the Mg5(Gd, Y) phase located at the grain boundary can improve the creep properties of the cast alloy in the early stage creep, the precipitates of β′ phase in T6 alloy and those formed during the creep process in as-solution alloy, which can effectively inhibit the dislocation gliding, can be attributed as an important factor in improving the high temperature creep performance of the alloys. Consequently, the alloy after T6 treatment exhibited the lowest creep rate and the as-solution alloy possessed a better creep resistance than that of the cast alloy during the steady-state creep.-
Key words:
- microstructure /
- Mg-8Gd-2Y-0.5Zr alloys /
- creep properties /
- precipitates
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图 1 不同状态Mg-8Gd-2Y-0.5Zr合金的光学显微组织 （a）铸态；（b）固溶态；（c）时效态；（d）挤压态
Figure 1. Optical microstructures of Mg-8Gd-2Y-0.5Zr alloys before creep （a）as-cast；（b）as-solution；（c）T6；（d）as-extruded
图 2 铸态Mg-8Gd-2Y-0.5Zr合金SEM形貌以及能谱分析 （a）SEM形貌；（b）铸态第二相能谱分析
Figure 2. SEM morphology and EDS of the second phase in the cast Mg-8Gd-2Y-0.5Zr alloy （a）SEM morphology；（b）EDS
图 3 不同组织状态下Mg-8Gd-2Y-0.5Zr合金的XRD衍射图谱
Figure 3. XRD pattern of Mg-8Gd-2Y-0.5Zr alloy with different initial microstructures before creep
图 4 时效态Mg-8Gd-2Y-0.5Zr合金的TEM形貌及基体相衍射分析 （a）TEM形貌；（b）基体相衍射斑点分析
Figure 4. TEM analysis of Mg-8Gd-2Y-0.5Zr alloy after T6 （a）TEM microstructure ；（b）SAED pattern of Mg matrix
图 5 挤压态Mg-8Gd-2Y-0.5Zr合金TEM显微组织
Figure 5. TEM analysis of the as-extruded Mg-8Gd-2Y-0.5Zr alloy
图 6 不同初始组织Mg-8Gd-2Y-0.5Zr合金的蠕变及相应蠕变速率曲线 （a）蠕变曲线；（b）局部放大蠕变曲线；（c）蠕变速率曲线
Figure 6. Creep strain curves and corresponding creep rates of Mg-8Gd-2Y-0.5Zr alloys with different microstructure （a）creep strain curves；（b）creep strain curves in large magnification；（c）creep rates curves
图 7 铸态合金蠕变过程中晶界Mg5(Gd, Y)相附近形貌微观组织演变 （a）晶界第二相；（b）晶界
Figure 7. Evolution of micromorphology near second phase Mg5(Gd, Y) during creep process （a）near Mg5(Gd, Y) phase；（b）grain boundary without second phase
图 8 蠕变后铸态以及固溶态合金的TEM显微组织 （a）铸态合金；（b）固溶态合金
Figure 8. TEM microstructure of the as-cast and as-solution alloys after creep （a） as-cast；（b）as-solution
表 1 实验合金化学成分 （质量分数/%)
Table 1. Chemical composition of the studied alloy (mass fraction%)
Gd Y Zr Mg 7.83 1.97 0.55 Bal 
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表 2 不同初始组织Mg-8Gd-2Y-0.5Zr合金的晶粒尺寸
Table 2. Grainsize of the Mg-8Gd-2Y-0.5Zr alloy with different initial microstructures
Alloys Grain size/μm As-cast 77.8 As-solution 79.0 As-T6 83.0 As-extruded 6.7
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表 3 不同初始组织Mg-8Gd-2Y-0.5Zr合金的稳态蠕变性能
Table 3. Creep properties of Mg-8Gd-2Y-0.5Zr alloy with different microstructures
Alloys Max creep strain/ % Steady-state creep rate As-cast 0.092 1.46×10−9 As-solution 0.082 1.24×10−9 As-T6 0.032 2.18×10-10 As-extruded 0.885 1.52×10−8
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