深冷处理时间对AZ31镁合金CMT接头耐蚀性的影响
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摘要
采用电化学阻抗谱(electrochemical impedance spectroscopy,EIS)方法研究了深冷处理时间对AZ31镁合金冷金属过渡(cold metal transfer,CMT)焊接接头腐蚀行为的影响。根据对腐蚀形貌及接头微观组织的观测,探讨了深冷处理提高接头耐蚀性的机理。结果表明:深冷处理后焊缝区中第二相尺寸、分布以及镁基体晶粒取向的改变是改善耐蚀性能的关键因素。深冷处理过程中接头内部骤增的内应力与内能致使焊缝区柱状晶和等轴晶得到细化,同时β相形态、分布发生变化。随深冷时间延长,晶粒细化程度越显著,第二相析出位置增多,尺寸逐渐增大,在基相中呈均匀弥散分布。与未深冷时相比,经-140℃深冷处理后的接头焊缝区耐蚀性能得到了不同程度的提高,随着深冷时间的增加,耐蚀性能排序为-140℃/4h>-140℃/8h>-140℃/2h>-140℃/6h。经-140℃/4h深冷处理的焊缝区电荷转移电阻和腐蚀产物膜电阻最大,耐蚀性能最佳。
Effect of cryogenic treatment time on corrosion behavior of AZ31 magnesium cold metal transfer(CMT)weld joint was studied by adopting electrochemical impedance spectroscopy(EIS).Based on the observation of corrosion morphology and microstructure of joints,the mechanism of cryogenic treatment to improve the corrosion resistance of joints was discussed.The results showed that the dimension and distribution of the second phase and the change of grain orientation of magnesium matrix are the key factors to improve the corrosion resistance of the weld after cryogenic treatment.The sudden increase of internal stress and energy in the joint during cryogenic treatment resulted in the refinement of columnar and equiaxed grains in the weld zone and the change of morphology and distribution ofβphases.With the cryogenic time increase,the grain refinement became more obvious,the precipitation position and dimension of the second phase increased.Theβphases distributed uniformly in the matrix phase.Compared to non-cryogenic joint,the corrosion resistance of joints that were cryogenic treated under-140℃ were increased to a different extent.With the time increase,the corrosion resistance was ranked as-140℃/4 h>-140℃/8 h>-140℃/2 h>-140℃/6 h.The weld zone that was cryogenic treated under-140 ℃/4 hshowed the best corrosion resistance because the charge transfer resistance and corrosion product film resistance of that reached maximum.
Effect of cryogenic treatment time on corrosion behavior of AZ31 magnesium cold metal transfer(CMT)weld joint was studied by adopting electrochemical impedance spectroscopy(EIS).Based on the observation of corrosion morphology and microstructure of joints,the mechanism of cryogenic treatment to improve the corrosion resistance of joints was discussed.The results showed that the dimension and distribution of the second phase and the change of grain orientation of magnesium matrix are the key factors to improve the corrosion resistance of the weld after cryogenic treatment.The sudden increase of internal stress and energy in the joint during cryogenic treatment resulted in the refinement of columnar and equiaxed grains in the weld zone and the change of morphology and distribution ofβphases.With the cryogenic time increase,the grain refinement became more obvious,the precipitation position and dimension of the second phase increased.Theβphases distributed uniformly in the matrix phase.Compared to non-cryogenic joint,the corrosion resistance of joints that were cryogenic treated under-140℃ were increased to a different extent.With the time increase,the corrosion resistance was ranked as-140℃/4 h>-140℃/8 h>-140℃/2 h>-140℃/6 h.The weld zone that was cryogenic treated under-140 ℃/4 hshowed the best corrosion resistance because the charge transfer resistance and corrosion product film resistance of that reached maximum.
引文
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[2]SDHOLZ A D,BIRBILIS N,BETTLES C J,et al.Corrosion behaviour of Mg-alloy AZ91E with atypical alloying additions[J].Journal of Alloys&Compounds,2007,471(1):109-115.
[3]薛文斌,陈廷芳,李永良,等.AZ31镁合金搅拌摩擦焊接头微弧氧化表面防护研究[J].材料工程,2012(12):1-6.XUE Wenbin,CHEN Tingfang,LI Yongliang,et al.Surface protection of friction stir welding joint for AZ31magnesium alloy coated by microarc oxidation[J].Journal of Materials Engineering,2012(12):1-6.(in Chinese)
[4]马颖,李伟荣.微弧氧化处理提高AZ31B镁合金搅拌摩擦焊焊缝的耐蚀性[J].兰州理工大学学报,2012,38(4):5-9.MA Ying,LI Weirong.Improvement in corrosion resistance of friction-stir welding joint of AZ31Bmagnesium alloy with micro-arc oxidation treatment[J].Journal of Lanzhou University of Technology,2012.38(4):5-9.(in Chinese)
[5]ISHAK M,YAMASAKI K,MAEKAWA K.Microstructure and corrosion behavior of laser welded magnesium alloys with silver nanoparticles[J].World Academy of Science Engineering&Technology,2010,4(9):853-858.
[6]戴军.稀土镁合金NZ30K激光焊接及接头性能改善研究[D].上海:上海交通大学,2012.DAI Jun.Research on laser welded Mg-rare earth alloy NZ30K and improvement of joint properties[D].Shanghai:Shanghai Jiao Tong University,2012.(in Chinese)
[7]WANG Ping,LU Wei,WANG Yuehui,et al.Effects of cryogenic treatment on the thermal physical properties of Cu76.12Al23.88alloy[J].Rare Metals,2011,30(6):644-649.
[8]CHEN Wenge,ZHOU Xun,ZHANG Qiang,et al.Influence of cryogenic treatment on wear properties of aluminum matrix composite material reinforced by Al2O3particle and fibre hybrid[J].Transactions of Materials&Heat Treatment,2006,27(5):10-12.
[9]BHALE P,SHASTRI H,MONDAL A K,et al.Effect of deep cryogenic treatment on microstructure and properties of AE42Mg alloy[J].Journal of Materials Engineering&Performance,2016,25(9):3590-3598.
[10]THORNTON R,SLATTER T,LEWIS R.Effects of deep cryogenic treatment on the wear development of H13A tungsten carbide inserts when machining AISI1045steel[J].Production Engineering,2014,8(3):355-364.
[11]陈金秋,吴志生,崔超,等.深冷温度对AZ31镁合金CMT焊接接头耐蚀性的影响[J].稀有金属材料与工程,2018,47(5):1543-1549.CHEN Jinqiu,WU Zhisheng,CUI Chao,et al.Effect of cryogenic treatment temperature on corrosion resistance of AZ31 magnesium alloy CMT weld joint[J].Rare Metal Materials and Engineering,2018,47(5):1543-1549.(in Chinese)
[12]GONG Xiaoyuan,WU Zhisheng,ZHAO Fei.Effect of deep cryogenic treatment on the microstructure and the corrosion resistance of AZ61 magnesium alloy welded joint[J].Metals-Open Access Metallurgy Journal,2017,7(5):179-186.
[13]SONG Guangling,XU Zhenqing.Effect of microstructure evolution on corrosion of different crystal surfaces of AZ31Mg alloy in a chloride containing solution[J].Corrosion Science,2012,54(1):97-105.
[14]ZHAO Mingchun,LIU Ming,SONG Guangling,et al.Influence of theβ-phase morphology on the corrosion of the Mg alloy AZ91[J].Corrosion Science,2008,50(7):1939-1953.
[15]陈鼎,夏树人,姜勇,等.镁合金深冷处理研究[J].湖南大学学报(自然科学版),2008,35(1):62-65.CHEN Ding,XIA Shuren,JIANG Yong,et al.Study on improving performance of magnesium alloy by deep cryogenic treatment[J].Journal of Hunan University(Natural Sciences),2008,35(1):62-65.(in Chinese)