Mg-Zn-Y-Zr合金低温拉伸与低温真空疲劳性能
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摘要
本文利用MTS材料试验机和MYBP疲劳试验机研究了锻造态Mg-Zn-Y-Zr合金在室温与低温(223K、173K、123K、77K)下的拉伸性能和室温大气、室温真空、低温真空环境下的疲劳性能,并采用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)分析技术考察了该合金的低温拉伸与低温真空疲劳变形断裂行为。
研究表明,锻造态Mg-Zn-Y-Zr合金主要由基体α-Mg、Mg3YZn6相和Mg3Y2Zn3相组成,Mg3YZn6相和Mg3Y2Zn3相可形成混合物,以较大尺寸的第二相颗粒分布于α-Mg晶界处,或以细小颗粒弥散分布在α-Mg晶粒内部。测试温度对Mg-Zn-Y-Zr合金的拉伸性能具有显著影响,随拉伸温度的降低,合金的抗拉强度和屈服强度增加,塑性降低,弹性模量增高。Mg-Zn-Y-Zr合金在室温下具有良好的塑性,延伸率可达15.5%,这与合金中稀土元素Y的存在有关,77K拉伸时合金的延伸率则降低到4.2%。随拉伸温度的降低,Mg-Zn-Y-Zr合金拉伸断口形貌逐渐表现出解理断裂的特征,拉伸温度越低,解理特征越明显。Mg-Zn-Y-Zr合金在低温下的变形主要以孪生为主,尽管仍可发现位错滑移的迹象。各种温度下,拉伸试样标距内的变形均较均匀。
Mg-Zn-Y-Zr合金在低温真空环境下的疲劳性能较室温大气有很大提高,疲劳寿命显著增加,室温真空环境下的疲劳性能则介于二者之间。三种环境下,疲劳源总是产生于存在第二相颗粒或者有缺陷的试样表面或次表面。其中,室温大气和室温真空环境下,微裂纹萌生于试样表面或者接近表面,而低温真空环境下则萌生于试样次表面。合金在室温大气环境下的疲劳断裂以塑性断裂为主,并且发现沿晶界处第二相颗粒聚集区域断裂的现象;低温真空疲劳断口解理断裂特征明显,并可发现裂纹沿特定晶体学平面扩展的痕迹。三种疲劳试样断口均存在疲劳辉纹,低温环境下的疲劳辉纹最清晰。断口附近显微组织中则可发现大量的疲劳变形孪晶和数量有限的滑移带,表明三种环境下Mg-Zn-Y-Zr合金的疲劳仍以孪生变形为主。
The tensile properties at 293K, 223K, 173K, 123K and 77K and fatigue properties in laboratory air, in vacuum at room temperature and in vacuum at cryogenic temperature of a forged Mg-Zn-Y-Zr alloy were investigated by use of universal material testing system (MTS) and fatigue testing machine. And the related tensile and fatigue deformation and fracture behaviors of this alloy were also investigated by means of optical microscope, scanning election microscope (SEM) and transmission electron microscope (TEM).
The results show that as-forged Mg-Zn-Y-Zr alloy mainly consisted ofα-Mg, Mg3YZn6 and Mg3Y2Zn3 phases. The Mg3YZn6 and Mg3Y2Zn3 phases have been found to be present at boundaries ofα-Mg grain or disperse withinα-Mg matrix. Testing temperature has a remarkable effect on tensile properties of the foraged alloy. Decreasing with the testing temperature, the tensile strength, yield strength and Young’s modulus of Mg-Zn-Y-Zr alloy increases, while the fracture strain decreases. The alloy exhibited a largest fracture strain of 15.5% as tested at 293K, resulting from the addition of Y elements to the alloy, and a lowest value of 4.2% was obtained at 77K. The fracture pattern of the tested Mg-Zn-Y-Zr samples was found to gradually represent cleavage fracture character as the test temperature decreased, the lower of testing temperature, and the more evident of cleavage fracture features. The deformation of the Mg-Zn-Y-Zr alloy at cryogenic temperature mainly induced by twining, despite that sign of dislocation slip could also be observed. Tensile deformation was found to occur uniformly within gauge of all the tested samples.
The fatigue property in cryogenic temperature-vacuum of Mg-Zn-Y-Zr alloy is the best under the three tested environments. The fatigue cracks were found to always initiate at surface or subsurface of the tested samples where second-phase particles or structure defects existed. The fatigue initiation sites were observed to be at surface of the samples tested in laboratory air or in vacuum at room temperature, while at the subsurface of the sample tested in vacuum at cryogenic temperature. Ductile fracture was mainly found in samples fatigued in laboratory air, and fracture of second phases at grain boundaries was also observed. Cleave fracture feature was evident in samples fatigued in vacuum at cryogenic temperature, and propagation of small cracks along the appropriate crystallographic plane was seen. Fatigue striations have been observed on fracture surface of all the samples tested in three environments, which are more apparent in vacuum at cryogenic temperature. Lots of twinning and limited slip bands were found in the area next to fracture surface of the fatigued samples, indicating that twinning seems to be the dominant deformation mechanism of Mg-Zn-Y-Zr alloy fatigued in these environments.
研究表明,锻造态Mg-Zn-Y-Zr合金主要由基体α-Mg、Mg3YZn6相和Mg3Y2Zn3相组成,Mg3YZn6相和Mg3Y2Zn3相可形成混合物,以较大尺寸的第二相颗粒分布于α-Mg晶界处,或以细小颗粒弥散分布在α-Mg晶粒内部。测试温度对Mg-Zn-Y-Zr合金的拉伸性能具有显著影响,随拉伸温度的降低,合金的抗拉强度和屈服强度增加,塑性降低,弹性模量增高。Mg-Zn-Y-Zr合金在室温下具有良好的塑性,延伸率可达15.5%,这与合金中稀土元素Y的存在有关,77K拉伸时合金的延伸率则降低到4.2%。随拉伸温度的降低,Mg-Zn-Y-Zr合金拉伸断口形貌逐渐表现出解理断裂的特征,拉伸温度越低,解理特征越明显。Mg-Zn-Y-Zr合金在低温下的变形主要以孪生为主,尽管仍可发现位错滑移的迹象。各种温度下,拉伸试样标距内的变形均较均匀。
Mg-Zn-Y-Zr合金在低温真空环境下的疲劳性能较室温大气有很大提高,疲劳寿命显著增加,室温真空环境下的疲劳性能则介于二者之间。三种环境下,疲劳源总是产生于存在第二相颗粒或者有缺陷的试样表面或次表面。其中,室温大气和室温真空环境下,微裂纹萌生于试样表面或者接近表面,而低温真空环境下则萌生于试样次表面。合金在室温大气环境下的疲劳断裂以塑性断裂为主,并且发现沿晶界处第二相颗粒聚集区域断裂的现象;低温真空疲劳断口解理断裂特征明显,并可发现裂纹沿特定晶体学平面扩展的痕迹。三种疲劳试样断口均存在疲劳辉纹,低温环境下的疲劳辉纹最清晰。断口附近显微组织中则可发现大量的疲劳变形孪晶和数量有限的滑移带,表明三种环境下Mg-Zn-Y-Zr合金的疲劳仍以孪生变形为主。
The tensile properties at 293K, 223K, 173K, 123K and 77K and fatigue properties in laboratory air, in vacuum at room temperature and in vacuum at cryogenic temperature of a forged Mg-Zn-Y-Zr alloy were investigated by use of universal material testing system (MTS) and fatigue testing machine. And the related tensile and fatigue deformation and fracture behaviors of this alloy were also investigated by means of optical microscope, scanning election microscope (SEM) and transmission electron microscope (TEM).
The results show that as-forged Mg-Zn-Y-Zr alloy mainly consisted ofα-Mg, Mg3YZn6 and Mg3Y2Zn3 phases. The Mg3YZn6 and Mg3Y2Zn3 phases have been found to be present at boundaries ofα-Mg grain or disperse withinα-Mg matrix. Testing temperature has a remarkable effect on tensile properties of the foraged alloy. Decreasing with the testing temperature, the tensile strength, yield strength and Young’s modulus of Mg-Zn-Y-Zr alloy increases, while the fracture strain decreases. The alloy exhibited a largest fracture strain of 15.5% as tested at 293K, resulting from the addition of Y elements to the alloy, and a lowest value of 4.2% was obtained at 77K. The fracture pattern of the tested Mg-Zn-Y-Zr samples was found to gradually represent cleavage fracture character as the test temperature decreased, the lower of testing temperature, and the more evident of cleavage fracture features. The deformation of the Mg-Zn-Y-Zr alloy at cryogenic temperature mainly induced by twining, despite that sign of dislocation slip could also be observed. Tensile deformation was found to occur uniformly within gauge of all the tested samples.
The fatigue property in cryogenic temperature-vacuum of Mg-Zn-Y-Zr alloy is the best under the three tested environments. The fatigue cracks were found to always initiate at surface or subsurface of the tested samples where second-phase particles or structure defects existed. The fatigue initiation sites were observed to be at surface of the samples tested in laboratory air or in vacuum at room temperature, while at the subsurface of the sample tested in vacuum at cryogenic temperature. Ductile fracture was mainly found in samples fatigued in laboratory air, and fracture of second phases at grain boundaries was also observed. Cleave fracture feature was evident in samples fatigued in vacuum at cryogenic temperature, and propagation of small cracks along the appropriate crystallographic plane was seen. Fatigue striations have been observed on fracture surface of all the samples tested in three environments, which are more apparent in vacuum at cryogenic temperature. Lots of twinning and limited slip bands were found in the area next to fracture surface of the fatigued samples, indicating that twinning seems to be the dominant deformation mechanism of Mg-Zn-Y-Zr alloy fatigued in these environments.
引文
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2大林辰藏.日地空间物理.冯克嘉译.北京师范出版社. 1984:1-4
3陈立佳,刘正,胡壮麒.镁合金疲劳行为的研究现状及展望.沈阳工业大学学报. 2005, 27(3):253-256
4周德钦,王贵福,王国军.镁合金的特点及其新技术发展.东北轻合金有限责任公司. 1997:75-80
5张津,王东亚,孙智富. AZ91D镁合金的低温力学性能.中国有色金属学报. 2004, 14(3):37-40
6 R. Ye. Lapovok and P. F. Thomson. Production of dense rod from magnesium swarf for RE-melting. Magnesium Technology, 2004:149-153
7 E-H. Han, W. Zhou, D. Shan and W. Ke. Chemical Conversion Coating on AZ91D and Its Corrosion Resistance. Magnesium Technology, 2004:121-125
8余琨,黎文献等.含稀土镁合金的研究与开发.特种铸造及有色合金. 2001,(1):41-43
9罗治平,张少卿等.稀土在镁合金溶液中作用的热力学分析.中国稀土学报.1995,3(2):119-122
10 Yi zhen Lu, Qudong Wang, Xiao qin Zeng. Effect of rare earths on the micro-structure, properties and fracture behavior of Mg-Al alloys. Materials Science and Engineering A. 1999, 278(1-2):66-76
11张诗昌,魏伯康等.钇及铈镧混合稀土对AZ91镁合金铸态组织的影响.中国有色金属学报. 2001, 11(2):99-102
12 S. S. Park, J. G. Lee, H. C. Lee and N. J. Kim. Development of Wrought Mg Alloys Via Strip Casting. Magnesium Technology. 2004:107-109
13邱惠中.空间站用材料的现状和进展.宇航材料工艺. l981:1-5
14张津,章宗和,等.镁合金及应用. 2004, 1(11):p294-297
15陈沛. Mg90.7Zn5.60Y3.17Zr0.53合金低温拉伸性能研究.哈尔滨工业大学. 2006:7-8
16 K-allxer, I. R. The Effect of Environment on the Behavioi'of Materials,2005:62-104
17 Hill, D C, Laler Si alation of Micromete-roid 1mpacts. JBIS. 1988, 4(2):59-405
18 Lee A. L., Production of Therm al cont rol Surface Deg radarioa Due t0 Atom jc Oxygen InteractioⅡ. m AA:85-1085
19 S. Suresh.材料的疲劳.王中光.第2版.国防工业出版社, 1999, 5:254-258
20王德尊.金属力学性能.哈尔滨工业大学出版社, 1993:160-161
21 Srivatsan S, Wei L, Chang C F. The cyclic strain resistance fatigue life and finalfracture behavior of magnesium alloys. Engineering Fracture Mechanics, 1997, 56(6):735-75
22许道奎,刘路,徐永波,韩恩厚.挤压态镁合金ZK60的超高周疲劳行为.金属学报. 2007, 43(2) :144-148
23 Papakyriacou M, Mayer H,Fuchs U, Et al. Influence of Atmo-spheric Moisture on Slow Fatigue Crack Growth at Ultrasonic Fre-quency in Aluminium and Magnesium Alloys. Fatigue andFracture of Engineering Materials and Structures. 2002, 25(8-9):795-804.
24 Heinzinger GD, Fenwick BP. Stability of learning control with disturbances and uncertain initial conditions. IEEE Transactions on Automatic Control, 1992, 37(10):110-114
25 Horstemeyer MF, Yang N, Gall K, Et al. High cyclefatigue of a die cast AZ91E-T4 magnesium alloy. Acta Materialia, 2004, 52(5):1327-1336
26 Eisenmeier G, Holzwarth B, Hoppel HW, et al. Cyclic Deforma-tion and Fatigue Behaviourof the Magnesium AlloyAZ91. Ma-terials Science and Engineering A. 2001, (319-321):578-582
27 Roymundo arroyoys and Zi-kui Liu. Thermodynamics of Mg-Zn-Zr: implication on the effect of Zr on grain refining of Mg-Zn alloys. Magnesium Technology 2005:203-206
28 Xi-shu Wanga, Jing-hong Fanb, An. evaluation on the growth rate of small fatigue cracks in cast AM50 magnesium alloy at different temperatures in vacuum conditions.International Journal of Fatigue. 2006, (28):79-86
29 Md Shahnewaz Bhuiyan, Yoshiharu Mutoh, Tsutomu Murai, Shinpei Iwakami. Corro-sion fatigue behavior of extruded magnesium alloy AZ61under three different corrosive environments. International Journal of Fatigue. 2008, (30):1756-1765
30 D. K. Xua, L. Liu, Y. B. Xu, E. H. Han. The micro-mechanism of fatigue crack propagate-on for a forged Mg–Zn–Y–Zr alloy in the gigacycle fatigue regime. Journal of Alloys and Compounds. 2008, (454):123-128
31 Z. G. Yang, S. X. Li, J. M. Zhang, J. F. Zhang, G. Y. Li, Z. B. Li, W. L. Hui, Y. Q. Weng. A-ctaMater. 2004, (52):5235
32 Eisenmeier G, Holzwarth B, Hppel H W, Et al.Cyclicdefoemation and fatigue behavior of the magnesium alloy AZ91. Materials Science and Engineering, 2001, A319 321:578-582.
33 Mayer H, Papakyriacou M, Zettl B, et al. Inflounce ofporosity on the fatigue limit of di-ecasting magnesium and alluminum alloys. International Journal of Fatigue, 2003, 25:245-256
34高洪涛,吴国华,丁文江.镁合金疲劳性能的研究现状.铸造技术, 2003, 24(4):266-268.
35 Z. P. Lou, D. Y. Song, S. Q. Zhang, J. Alloys Compd. 1995, (230):109
36 C. Laird, G.C. Smith, Philos.Magn.8 (1962):847
37余琨,黎文献,王日初.热处理工艺对挤压变形ZK60镁合金组织与力学性能的影响.中国有色金属学报. 2007, 7(2):188-191.
38 Soeren Mueller, Klaus Mueller, Walter Reimers, Marius Rosumek. Microstructure development of extruded Mg alloys. Magnesium Technology 2005:165-168
39 Chun jiang Ma, Man ping Liu, Guo hua WU, Weng iangg Ding, Yan ping Zhu, Ma-terSei. EngA, 2003, (207):349
40 Avedesian M M, Bae rker H. ASM Speciality handbook”magnesium an magnesium alloys”. the materials information society, 2004:9-13
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