高塑性Mg-3Gd-1Zn合金高温变形机理及挤管材的组织和力学性能研究

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	高塑性Mg-3Gd-1Zn合金高温变形机理及挤管材的组织和力学性能研究
	陈晓霞
学位类型	硕士
导师	陈荣石
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	镁合金无缝管材力学性能织构动态再结晶剪切带 Mgnesium Alloy Seamless Tube Mechanical Property Texture Drx Shear Band
摘要	"镁合金被誉为 “二十一世纪绿色结构材料”。相对于铸造镁合金，变形镁合金具有更优异的力学性能。但镁合金加工成形困难，品种少，可工业化生产的型材更难得到，从而严重限制了它的广泛应用。本论文选用新型Mg-3Gd-1Zn（GZ31）高塑性合金为对象，利用金相技术、XRD、扫描电镜以及EBSD技术和力学性能试验表征了高温变形时的组织演变以及挤压无缝管材组织和力学性能，分析了GZ31合金高温变形机理及变形温度和挤压工艺对管材组织和力学性能的影响规律。利用高温单轴压缩试验研究了变形温度和变形速率对粗晶铸态GZ31合金动态再结晶规律的影响。结果表明：第二相对再结晶晶粒的长大有阻碍作用；再结晶晶粒尺寸d和Z参数偏离双对数线性关系；相比于应变速率，温度对再结晶尺寸的影响更加明显，这可能与温度对第二相（W相）的分布和尺寸影响更大有关。450~500℃变形时主要发生孪生诱发动态再结晶；550℃变形时发生不连续动态再结晶。研究了初始织构对GZ31合金高温变形行为和动态再结晶规律的影响。结果表明：具有初始基面纤维织构的合金板材，沿着挤压方向和板面法向高温压缩时表现出明显不同的流变行为，随变形温度升高流变行为的差异逐渐减小。低温400℃时，沿板面法向压缩表现出差的加工性能，变形量35%时发生断裂；变形机制主要为基面滑移和剪切变形，动态再结晶晶粒在剪切带处产生；沿挤压方向压缩组织变形均匀，变形机制主要为拉伸孪生，动态再结晶晶粒发生在初始晶界处；初始织构对再结晶晶粒尺寸没有影响。采用常规空心锭热挤压工艺获得了表面质量好的GZ31管材，研究了挤压温度、挤压工艺对管材组织和室温力学性能的影响。结果表明：GZ31合金较AZ31合金更难发生再结晶，管材具有更弱的基面纤维织构。420℃一次挤压成形的GZ31管材的再结晶晶粒十分细小，但由于组织中还存在粗大的原始晶粒，导致其室温伸长率较低；440℃及以上挤压时得到完全再结晶组织，且随挤压温度升高，再结晶晶粒和第二相（W相）尺寸逐渐增大；经过一次挤压开坯后再在440℃二次挤压的GZ31无缝管材具有更细小的平均晶粒尺寸（约12μm），室温拉伸时孪生几乎被抑制，从而室温伸长率高达35%，明显优于传统AZ31以及一次挤压成形的GZ31镁合金无缝管材。
其他摘要	"Magnesium alloys are recognized as the “green structural materials” in the 21th century.The wrought magnesium alloy has more excellent mechanical properties than cast magnesium alloy. But magnesium alloy has poor processability and formability so as to a few alloy-series are gotten, especially the shaped material produced in industry, which limits their widely application. In this dissertation, a newly developed high ductile Mg-3Gd-1Zn (GZ31) alloy was chosen to be investigated in aspects of the high temperature deformation mechanism and microstructure, mechanical properties of its extruded seamless tubes by metallographical analysis, SEM and EBSD technique. The dynamic recrystallization behavior in as-cast GZ31alloy with coarse-grain during uniaxial hot compression was investigated. The results indicate that the conventional relationship between DRXed grain size and the Z parameter breaks down due to the second phase（W phase） inhibiting DRXed grain growth. Compared with the strain rate, the deformation temperature has more significant influence on the DRXed grain size. This is maybe because temperature has more influence on the W phase size and distribution. At 450~500℃, DRX mechanism is TDRX , at 550℃, the mechanism is DDRX. The effect of initial texture on dynamic recrystallization behavior was researched. The results show that the GZ31 alloy plate with initial basal plane fiber texture has significantly different flow stress behavior along the extrusion direction and normal direction. As temperature increases the difference decreases gradually. At low temperature 400℃, it has worse processability and fractures at strain of 35% along the ND. And cracks originate from the trifurcate grain boundaries. Basal plane slid and shear bands occur, DRXed grains are located in shear bands; it doesn’t facture along the ED and the deformed microstructure is uniform, tensile twining are the main deformation mechanism. DRXed grains are located at the initial grain boundaries. But DRXed grain size is not affected by initial texture. The effect of initial texture on DRX behavior decreases Conventional extrusion technique was used to get the GZ31 seamless tubes with good surface quality. The effect of extrusion temperatures and initial microstructures on microstructure and mechanical properties of GZ31 tubes was researched. Results show that it is more difficult to get the totally recrystallization microstructure and has weaker basal plane fiber texture than AZ31 alloy. The one-step extruded GZ31 tube at 420℃ has pretty fine recrystallized grains .But due to the remaining initial coarse grains, so it has low room temperature tensile elongation. Totally recrystallized microstructure is gotten at 440℃ and higher temperatures extrusion tubes, and the DRXedgrains and W phase become coarser gradually. GZ31 tube extruded at 440℃ after first extrusion billeting has finer grains (12μm) so as to get the maximum room temperature tensile elongation of 35%, which is much better than that of commercial AZ31 tubes and GZ31 tubes formed by one-step extrusion"
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64513
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	陈晓霞. 高塑性Mg-3Gd-1Zn合金高温变形机理及挤管材的组织和力学性能研究[D]. 北京. 中国科学院金属研究所,2012.