镁合金MIG焊接工艺及焊接接头组织性能分析.pdf

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1、 1994-2010 China Academic Journal Electronic Publishing House.All rights reserved.http:/收稿日期:2008-08-07镁合金MIG焊接工艺及焊接接头组织性能分析 王 鹏,宋 刚,刘黎明(大连理工大学 材料科学与工程学院,辽宁 大连 116024)摘 要:采用脉冲MIG焊接工艺,进行AZ31B镁合金板材的焊接性分析,焊后利用光学显微镜、扫描电子显微镜、万能拉伸试验机和显微硬度仪等设备对焊接接头的组织与力学性能进行了检测分析.结果表明,通过优化工艺参数,采用脉冲MIG焊接工艺可以在不开坡口、不需背面强制成形的条

2、件下,实现镁合金单面焊接双面成形,获得连续、没有表面缺陷的焊接接头.焊接接头的热影响区较窄,晶粒稍有长大.焊缝区组织均匀,晶粒细小,硬度值高于母材.焊接接头的抗拉强度可达到母材的95%以上.关键词:脉冲;熔化极惰性气体保护焊;镁合金;焊接工艺;组织性能中图分类号:TG115.28 文献标识码:A 文章编号:0253-360X(2009)12-0109-04王 鹏0 序 言镁合金具有密度低、比强度和比刚度高、电磁屏蔽和抗辐射性能好以及易回收等优点,被称为21世纪绿色工程材料,在航空、汽车、电子等领域具有巨大的应用潜力1.当前镁合金焊接技术研究主要集于电弧焊、激光焊2、电子束焊、激光2TIG复合焊

3、3、搅拌摩擦焊等.而电弧焊在实际的应用中最方便,最易被企业实现应用,包括钨极惰性气体保护焊(TIG焊)和熔化极气体保护焊(MIG焊).钨极惰性气体保护焊(TIG焊)是目前镁合金最常用的一种焊接方法.尽管TIG焊被广泛应用于镁合金的焊接中,但是这种方法存在以下两个主要缺点.(1)焊接接头力学性能低,尤其是大部分牌号的镁合金焊接接头的断后伸长率以及疲劳性能显著低于母材基体.焊接接头热影响区宽且晶粒比较粗大,并且伴有连续相析出,会严重影响焊接接头的力学性能,尤其是疲劳强度等动载荷性能.(2)镁合金TIG焊的焊接效率较低,只能适用于薄板焊接.与TIG焊相比,MIG焊的优点在于焊接速度快,在全自动焊接过

4、程中能够实现1 mmin的高速焊接.而且镁合金的MIG焊可实现对厚板的焊接,进行单面焊双面成形.镁合金普通MIG焊也存在以下几个缺点.(1)由于以焊丝作电极,适宜的焊接工艺较窄;(2)由于熔融镁的表面张力小,电极丝前端的熔滴难以脱离且焊接电流过高时熔滴爆炸蒸发易造成飞溅;(3)由于电极丝软,送丝稳定性差;(4)市场上直径小于1.6 mm的焊丝经常缺货,对于焊接厚度小于2 mm的工件,难以找到适配焊丝.因此限制了镁合金MIG焊的实际应用4.研究新型镁合金MIG焊接方法,对镁合金在工业中的应用具有重要意义.1 试验方法试验采用尺寸为100 mm100 mm3.5 mm的AZ31B镁合金板材,进行脉

5、冲MIG焊试验,接头采用对接形式.其化学成分见表1,微观组织如图1所示;使用焊丝的化学成分见表2.表1 镁合金AZ31B板材化学成分(质量分数,%)Table 1Chemical composition of AZ31B magnesium alloyAlZnMnCaSiCuNiFeMg2.53.5 0.51.5 0.20.5 0.04 0.10 0.05 0.005 0.005余量图1AZ31B镁合金微观组织形貌Fig11Microstructure of AZ31B第30卷 第12期2 0 0 9年1 2月焊 接 学 报TRANSACTIONS OF THE CHINA WELDING I

6、NSTITUTIONVol.30No.12December2009 1994-2010 China Academic Journal Electronic Publishing House.All rights reserved.http:/表2 镁合金焊丝化学成分(质量分数,%)Table 2Chemical composition of AZ61A magnesium alloyAlZnMnCaSiCuNiFeMg5.87.2 0.41.5 0.20.5 0.04 0.10 0.05 0.005 0.0005余量所使用的焊机为脉冲MIGMAG焊机,保护气为纯度99.99%的氩气.焊接前应对

7、试件进行充分打磨,除去材料表面氧化膜.焊接后,经切割、研磨、抛光和腐蚀后,制备成试件.采用金相显微镜进行分析,得到接头的金相显微组织照片.采用CSS2205型电子万能试验机进行焊接接头的拉伸试验,拉伸速度为2 mmmin.测量试件硬度负载为49 N,加载时间为20 s.拉伸试样按国家标准G B265181焊接接头拉伸试验法 中规定取样.2 试验结果及分析2.1 焊接工艺参数试验采用平板对接焊,采用高纯氩气作为保护气体,单面焊双面成形.由于焊接参数多而复杂,为了寻找最佳的焊接工艺参数,分析了MIG焊接基值电流、脉冲后处理电流、焊接速度、脉冲频率和送丝速度等主要参数对焊缝表面成形、熔深、熔宽等指标

8、的影响,参数变化范围见表3.表3 焊接工艺参数的变化范围Table 3Variety of welding parameters基值电流IbA脉冲后处理电流IrA焊接速度v(mmmin-1)脉冲频率fHz送丝速度vw(mmin-1)5090400156.050110700356.5501301 000557.0501501 300757.5501701 600958.0501902 0001158.5试验结果表明,随着脉冲后处理电流的增大,焊缝的熔深和熔宽随之增大;当焊接速度增大时,焊缝的熔深和熔宽会随之减小.随着脉冲频率的增加,焊缝的熔深和熔宽呈现降低的趋势.通过上述试验的观察以及对焊接过程

9、中的电弧稳定性和飞溅进行调整,得出最佳的焊接参数为基值电流50 A,脉冲频率6575 Hz,脉冲后处理电流140170 A,送丝速度6.58.0 mmin,焊接速度7001 200 mmmin.并得到成形良好的焊缝,上表面连续、平整,形成了鱼鳞状波纹,并且没有咬边、裂纹、表面气孔等明显缺陷,如图2所示.图2 焊缝外观形貌Fig12Weld appearances2.2 拉伸试验及分析在优化的参数下,得到五个镁合金脉冲MIG焊接试样,并进行拉伸试验,试验前试样上下表面磨平,去除余高.试验结果见表4.表4 拉伸试样的力学性能Table 4Tensile properties of specimen

10、样本序号抗拉强度RmMPa断裂位置母材256标距线内1244焊缝2247热影响区3201焊缝4241焊缝5243焊缝由表4可知,样本1,样本2和样本5抗拉强度可以达到母材的95%以上,样本4也达到母材强度的94%,但样本3强度只有母材的79%.为了寻找样本3强度损失的原因,利用扫描电镜观察了断口的微观形貌.图3a为样本1的典型断口形貌,它具有部分脆性断裂的形貌特征,但里面又有大量的韧窝,因此属于混合断裂形貌.而由图3b中明显看到,有许多杂质散落于断口中,这是影响其力学性能的主要原因,如图中箭头处所示.这些杂质可能是焊丝或者母材焊前没有清理干净造成的.样本1,样本4和样本5断于焊缝,可能与微气孔

11、有关.2.3 微观组织特征分析沿垂直于焊缝方向取样,将制好的金相试样用110焊 接 学 报第30卷 1994-2010 China Academic Journal Electronic Publishing House.All rights reserved.http:/图3 拉伸断口的微观形貌Fig13Tensile fracture morphology苦味酸溶液进行腐蚀,在光学显微镜下观察焊接接头的组织特征.图4为MIG焊接接头AZ31B的宏观形貌,可以看出焊缝成形良好,焊缝内无气孔、裂纹和夹杂等明显缺陷.整个焊接接头变形很小.为深入认识接头的组织特征,对接头进行了微观组织观察,见图5

12、.图4 接头宏观形貌Fig14Macrophotograph of welded joint图5a为典型的焊接接头组织形貌,从图5a中可以看出焊缝区和热影响区的分界十分明显.焊缝区是有大量析出物的部分,而热影响区是晶粒上有大量点状析出物分布的部分.焊缝区的室温组织是镁和金属间化合物Mg17Al12的共晶组织.热影响区很窄,并且沿熔合线从上到下,宽度由窄变宽,虽然其晶粒与母材相比有所长大,但是并不是特别明显.而焊缝区的晶粒则明显比热影响区和母材细小,是图5MIG焊AZ31B的焊缝显微组织形貌Fig15Microstructure of AZ31B magnesium weld in MIGwel

13、ding典型的铸造急冷组织5.进一步观察焊缝区组织形貌,见图5b,发现焊缝区由细小的等轴晶粒组成,而且整个焊缝区组织也很均匀.对此,文献6中也有论述.热影响区的晶粒比焊缝区和母材的粗大,这将导致该区的力学性能有所降低,力学性能测试发现强度最高的试样断裂在热影响区内.但由于焊缝区会存在杂质或者微气孔,因而使接头性能严重降低,断裂在焊缝内.对接头的微观硬度测量可以反映接头中微观组织的细微变化,如图6所示,测试部位是图4中的虚线处.焊缝的硬度值高于母材,但是变化不明显.沿焊缝由上到下,硬度值的变化趋势呈现由小变大,再变小的趋势.接头区的硬度与其平均晶粒直径的平方根成反比7.焊缝区金属在电弧的作用下重

14、熔结晶,晶粒相对于母材金属得到了明显的细化,硬度值升高.另外,由于焊缝析出相较多,因而也造成焊缝硬度的提高8.由图4可以看出,焊缝底部由于熔化的焊丝金属与母材混合不充分,底部还是母材成分,这是此处比焊缝中心部分硬度低的原因.另一方面,焊缝硬度的提高与铝含量也有关,铝含量的增加不仅有利于焊缝晶粒的细化,而且使焊缝析出相较多.第12期王 鹏,等:镁合金MIG焊接工艺及焊接接头组织性能分析111 1994-2010 China Academic Journal Electronic Publishing House.All rights reserved.http:/图6 接头区的硬度分布Fig16

15、Distribution of hardness in joint3 结 论(1)采用脉冲MIG焊工艺可以在不开坡口的条件下实现单面焊双面成形,获得镁合金板材AZ31B高质量的焊接接头.其表面成形良好,无明显缺陷.(2)焊接接头抗拉强度可达母材95%以上,力学性能良好.(3)焊接接头的热影响区较窄,晶粒稍有长大.焊缝区组织均匀,晶粒细小,主要由细小的等轴晶组成,该区域硬度值均高于母材.(4)焊接接头断口为混合断口,当断口处存在夹杂物时,会严重降低接头的力学性能.参考文献:1Nunes A C,Bayless E O,Jones C O,et al.Variable polarity plasm

16、aarc welding on the space shuttle external tankJ.Welding Journal,1984,63(9):27-35.2 王继锋,刘黎明,宋 刚.激光焊接AZ31B镁合金接头微观组织特征J.焊接学报,2004,25(3):15-18.Wang Jifeng,Liu Liming,Song Gang.Microstructure character ofY AGlaser welding AZ31B Mg alloyJ.Transactions of the ChinaWelding Institution,2004,25(3):15-18.3宋 刚

17、,刘黎明,王继锋,等.激光2TIG复合焊接镁合金AZ31B焊接工艺J.焊接学报,2004,25(3):31-34.Song Gang,LiuLiming,WangJifeng,et al.Laser tungsten inert2gasarc hybrid welding process on wrought magnesium alloy AZ31BJ.Transactions of the China Welding Institution,2004,25(3):31-34.4 胡学安,徐道荣.镁合金的焊接方法及其工艺要素J.轻金属加工技术,2006,34(8):11-12.Hu Xuea

18、n,Xu Daorong.Review on the welding methods and proce2dure factorsof magnesium alloysJ.Light Alloy Fabrication Technolo2gy,2006,34(8):11-12.5 苗玉刚,刘黎明,赵 杰,等.变形镁合金熔焊接头组织特征分析J.焊接学报,2003,24(2):63-66.Miao Yugang,Liu Liming,Zhao Jie,et al.Microstructure featureanalysis of fusion welded joint of wrought Mg2

19、alloyJ.Transactions ofthe China Welding Institution,2003,24(2):63-66.6 董长富,刘黎明,赵 旭.变形镁合金填丝TIG焊接工艺及组织性能分析J.焊接学报,2005,26(2):33-36.Dong Changfu,Liu Liming,Zhao Xu.Welding technology and micro2structure of tungsten inert2gas welded magnesium alloyJ.Transac2tions of the China Welding Institution,2005,26(

20、2):33-36.7Su S F,HuangJ C,Lin H K,et al.Electron2beam welding behaviorin Mg2Al2based alloysJ.Metallurgical and Materials Transactions,2002,33A(5):1461-1473.8Amjad Saleh EI2Amoush.Effect of aluminum content on mechanicalproperties of hydrogenated Mg2Al magnesium alloysJ.Journal of Al2loys and Compoun

21、ds,2008,463(8):475-479.作者简介:王 鹏,男,1984年出生,硕士研究生.主要从事镁合金MIG焊研究.Email:112焊 接 学 报第30卷 1994-2010 China Academic Journal Electronic Publishing House.All rights reserved.http:/Numerical simulation of slit type cracking test for 9%Ni steelBAI Shiwu1,2,LI Wushen1,Y AN Chunyan1,3,YIN Zhanghua2,HUANG Fuxiang2

22、(1.School of Materials Science and Engineering,Tianjin University,Tianjin 300072,China;2.Petroleum2Gas Pipe2line Research Institute of China,Langfang 065000,China;3.Col2lege of Mechanical and Electrical Engineering,Hohai University,Changzhou 213022,China).p 93-96Abstract:With SYSWELD software,the te

23、mperature andstress field of 9%Ni steel Y2slit weldments with different preheattemperatures weresimulatedby applying double2ellipsoidheatsource.Distribution lawsof welding temperature and stressfield werestudied.Effects of preheat temperature on welding heat cycles andresidual stress were analyzed.R

24、esults show that with increasing pre2heat temperature,cooling rate decreases facilitates escaping ofhydrogen and self2tempering of martensite,the average stress leveland cold2cracking susceptibility of the weldments increase,so highpreheat temperature shall be avoided for 9%Ni steel welding.Key word

25、s:9%Ni steel;slit type cracking test;preheattemperature;temperature field;stress fieldAnalysis on heat2affected zone toughness of railroad freightTCS345 stainless steel weld jointsWANGBaosen,MA Zhao2hui,ZHU Shuangchun,XU Ke(Research Institute,Baosteel Iron&Steel Co.Ltd,Shanghai 201900,China).p 97-10

26、0Abstract:The transformation temperature phase diagram of12%chromium steel isobtained by using Thermal2cal software.Pro2cess of welding 12%chromium stainless steel is analysed with thephase transformation temperature scope.The heat2affected zone(HAZ)of the weld joints is observed with optic microsco

27、pe andscanning electronic microscope,which the microstructure consists offerrite,martensite,coarse grain heat2affected zone(CGHAZ),finegrain heat2affected zone(FGHAZ)and Ti(CN).The key elementsthat affect toughness of CGHAZ are ferritic grain size and martensiticcontent.The base material has the bes

28、t impact toughness when grainsize of Ti(CN)reaches 2-5m.The lowest ductility2brittle transi2tion temperature in CGHAZ is-22when content of carbon plusnitrogen in base material is about 0.02%and martensitic content inCGHAZ is 40%under some certain welding procedure.Key words:chromium ferritic stainle

29、ss steel;coarse grainheat affected zone;impact toughnessMicrostructural formation of austenitic stainless steel joint bycapacitor discharge weldingXU Feng1,2,XU Jinfeng2,ZHAIQiuya2(1.School of Materials Science and Engineering,ShaanxiUniversity of Technology,Hanzhong 723003,China;2.Xian Uni2versity

30、of Technology,Xian 710048,China).p 101-104Abstract:The 0Cr18Ni9 austenitic stainless steel sheet with0.2 mm thickness was welded in capacitor discharge spot welding.The temperature field and cooling rate of nugget was calculated.Theresults show that the joint microstructure consists of nugget zone a

31、ndsemi2melt zone.Due to very short time in welding,the cooling rateof the joint reaches to 5.1106Ks,the growth of austenite micro2structure is impeded,and the microstructure of the nugget is refined,which has rapidly solidified characteristics.As the austenite micro2structure of the nugget stays in

32、temperature province of activationwith very short time,the chrome of austenite grain boundary precipi2tations is checked.T o obtain the high quality spot2weld joint,thewelding parameters are determined as:welding voltage 80 V,capac2itor 6 600F and electrode pressure 18 N.Key words:austenitic stainle

33、ss steel;capacitor dischargewelding;spot2weld jointAnalysis for the influences of aluminum alloy P2MIG weldingparameters on welding arcLU Zhiqiang1,2,HUA Xueming1,2,LI Fang1,2,WU Y ixiong1,2(1.Material and Science EngineeringDepartment,Shanghai Jiaotong University,Shanghai 200240,Chi2na;2.The Key La

34、boratory of Laser Processing and Material Modifi2cation of Shanghai,Shanghai 200240,China).p 105-108Abstract:Under the same average welding current and weld2ing voltage,by regulating the different based current and peak cur2rent,the Al2Mg alloy was welded with Al2Mgfiller wire.The photosof welding a

35、rc were obtained by using high2speed video photography.Peak current has great influence on the shape and characteristics ofthe arc.With increasing the peak current value,rotated arc appearsand pulsed rotated metal transfer behavior occurs.Based current haslittle influence on the arc shape.Base curre

36、nt is the important pa2rameter for keeping arc burning.At pulse off time,it must be givenbase current value which is large enough to keep the arc burning sta2bly.In this study,the arc shape is defined by arc length,arc widthand arc portrait cross2section area,which will be influenced by theweld curr

37、ent.Peak current is important parameter of arc temperatureand pulse energy.The study shows that when the arc is burning atpulse on time,the arc length,arc width and arc portrait cross2sec2tion area increase with raising peak current.Key words:aluminum alloy;arc shape;pulsed2insert gaswelding;current

38、Welding technology and microstructure of MIG welded magne2sium alloyWANG Peng,SONG Gang,LIU Liming(School ofMaterials Science and Engineering,Dalian Universityof Technology,Dalian 116024,China).p 109-112Abstract:The pulsed MIGwelding was used to weld AZ31BMg alloy,and the weldability of the alloy wa

39、s studied.The micro2structure,mechanical property and hardness of the welded joint wereinvestigated via the metal phase microscopy,scanning electron mi2croscope,tensile testing machine and hardness instrument.The re2sults show that one2side welding with back can be obtained throughthis technique at

40、optimized parameters when there was no groove andno shaped ban,which continuous butt joints have no surface defects.The heat2affected zone of the joints is narrow,and the grains of thezone are slightly larger than that of the base metal.The grains of fu2sion zone are tiny,the microstructure is homogeneous and the hard2ness of welded joint is higher than that of the base metal.The tensilestrength is up to 95%of the base metal.Key words:pulsed MIGwelding;magnesium alloy;weldingprocess;microstructure MAIN TOPICS,ABSTRACTS&KEYWORDS2009,Vol.30,No.12