收稿日期:2008-08-07
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AZ 31B 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:TG 115.28 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]
古书装订、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).
8gggg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β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，在全自动焊接过程中能够实现1m Πmin 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1.6mm 的焊丝经常缺货，对于焊接厚度小于2mm 的工件，难以到适配焊丝.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100mm ×100mm ×3.5mm 的AZ 31B 镁合金板材，进行脉冲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 1 Chemical compo sition of AZ31B magne sium alloy
Al
Zn
Mn
Ca
S i
Cu
Ni
Fe
M g
2.5～
3.50.5～1.50.2～0.50.040.100.050.0050.005
余量
图1 AZ31B 镁合金微观组织形貌Fig 11 M icro structure of AZ31B
第30卷第12期2009年12月
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V ol.30 N o.12December 2009
表2 镁合金焊丝化学成分(质量分数,%)
Table2 Chemical compo sition of AZ61A magne sium alloy Al Zn Mn Ca S i Cu Ni Fe M g 5.8～7.20.4～1.50.2～0.50.040.100.050.0050.0005余量
所使用的焊机为脉冲MIGΠMAG焊机，保护气为纯度99.99%的氩气.焊接前应对试件进行充分打磨，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CSS 2205型电子万能试验机进行焊接接头的拉伸试验，拉伸
速度为2mmΠmin.测量试件硬度负载为49N，加载时间为20s.拉伸试样按国家标准G B2651 81《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
Table3 Variety of welding parameters
基值电流I bΠA 脉冲后处理
电流I rΠA
焊接速度
vΠ(mm・m in-1)
脉冲频率
fΠH z
送丝速度
v wΠ(m・m in-1)
509040015 6.0
5011070035 6.5
501301000557.0
501501300757.5
501701600958.0
5019020001158.5
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50A，脉冲频率65～75H z，脉冲后处理电流140～170A，送丝速度6.5～8.0mΠmin，焊接速度700～1200mmΠmin.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
Fig12 Weld appearance s
2.2 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
Table4 Tensile propertie s of specimen
样本序号抗拉强度R mΠMPa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
图3 拉伸断口的微观形貌
Fig 13 Tensile fracture morphology
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AZ 31B 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.
图4 接头宏观形貌
太阳能恒温器Fig 14 Macrophotograph 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Mg 17Al 12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5 MIG 焊AZ31B 的焊缝显微组织形貌
Fig 15 M icro structure of AZ31B magne sium weld in MIG
welding
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.
无人机北京天宇创通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
图6 接头区的硬度分布
Fig16 Distribution of hardne ss in joint
3 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:
[1] Nunes A C,Bayless E O,Jones C O,et al.Variable polarity plasma
arc welding on the space shuttle external tank[J].W elding Journal, 1984,63(9):27-35.
镇流器外壳[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.
W ang Jifeng,Liu Lim ing,S ong G ang.M icrostructure character of Y AGlaser welding AZ31B M g alloy[J].T ransactions of the China W elding Institution,2004,25(3):15-18.
[3] 宋 刚，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.
S ong G ang,Liu Lim ing,W ang Jifeng,et al.Laser tungsten inert2gas arc hybrid welding process on wrought magnesium alloy AZ31B[J].
T ransactions of the China W elding 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 Xuean,Xu Daorong.Review on the welding methods and proce2 dure factors of magnesium alloys[J].Light Alloy Fabrication T echnolo2 gy,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.
M iao Y ugang,Liu Lim ing,Zhao Jie,et al.M icrostructure feature analysis of fusion welded joint of wrought M g2alloy[J].T ransactions of the China W elding 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
充气包装袋织性能分析[J].焊接学报,2005,26(2):33-36.
D ong Chang fu,Liu Lim ing,Zhao Xu.W elding technology and m icro2
structure of tungsten inert2gas welded magnesium alloy[J].T ransac2 tions of the China W elding Institution,2005,26(2):33-36. [7] Su S F,Huang J C,Lin H K,et al.E lectron2beam welding behavior
in M g2Al2based alloys[J].M etallurgical and M aterials T ransactions, 2002,33A(5):1461-1473.
[8] Am jad Saleh EI2Am oush.E ffect of alum inum content on mechanical
properties of hydrogenated M g2Al magnesium alloys[J].Journal of Al2 loys and C om pounds,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:liulm@dlut.edu
112
焊 接 学 报第30卷
Numerical simulation of slit type cracking test for 9%Ni steel
BAI Shiwu 1,2,LI Wushen 1,Y AN Chunyan 1,3,YI N Zhanghua 2,H UANG Fuxiang 2
(1.School of Materials Science and Engineering ,
T ianjin University ,T ianjin 300072,China ;2.Petroleum 2G as Pipe 2line Research Institute of China ,Lang fang 065000,China ;3.C ol 2lege of Mechanical and E lectrical Engineering ,H ohai University ,Changzhou 213022,China ).p 93-96
Abstract : With SY SWE LD s oftware ,the tem perature and stress field of 9%Ni steel Y 2slit weldments with different preheat tem peratures were simulated by applying double 2ellips oid heat s ource.Distribution laws of welding tem perature and stress field were studied.E ffects of preheat tem perature on welding heat cycles and residual stress were analyzed.Results show that with increasing pre 2heat tem perature ,cooling rate decreases facilitates escaping of hydrogen and self 2tem pering of martensite ,the average stress level and cold 2cracking susceptibility of the weldments increase ,s o high preheat tem perature shall be av oided for 9%Ni steel welding.
K ey w ords : 9%Ni steel ;slit type cracking test ;preheat tem perature ;tem perature field ;stress field
Analysis on heat 2affected zone toughness of railroad freight TCS345stainless steel w eld joints W ANG Baosen ,M A Zhao 2
hui ,ZH U Shuangchun ,X U K e (Research Institute ,Baosteel Iron &S teel C o.Ltd ,Shanghai 201900,China ).p 97-100
Abstract : The trans formation tem perature phase diagram of 12%chromium steel is obtained by using Thermal 2cal s oftware.Pro 2cess of welding 12%chromium stainless steel is analysed with the phase trans formation tem perature scope.The heat 2affected zone (H AZ )of the weld joints is observed with optic microscope and scanning electronic microscope ,which the microstructure consists of ferrite ,martensite ,coarse grain heat 2affected zone (CG H AZ ),fine grain heat 2affected zone (FG H AZ )and T i (C ΠN ).The key elements that affect toughness of CG H AZ are ferritic grain size and martensitic content.The base material has the best im pact toughness when grain size of T i (C ΠN )reaches 2-5μm.The lowest ductility 2brittle transi 2tion tem perature in CG H AZ is -22℃when content of carbon plus nitrogen in base material is about 0.02%and martensitic content in CG H AZ is 40%under s ome certain welding procedure.
K ey w ords : chromium ferritic stainless steel ;coarse grain heat affected zone ;im pact toughness
Microstructural form ation of austenitic stainless steel joint by cap acitor disch arge w elding X U Feng 1,2
,X U Jin feng 2
,ZH AI
Qiuya 2
(1.School of Materials Science and Engineering ,Shaanxi University of T echnology ,Hanzhong 723003,China ;2.X i ’an Uni 2versity of T echnology ,X i ’an 710048,China ).p 101-104
Abstract : The 0Cr18Ni9austenitic stainless steel sheet with 0.2mm thickness was welded in capacitor discharge spot welding.The tem perature field and cooling rate of nugget was calculated.The results show that the joint microstructure consists of nugget zone and semi 2melt zone.Due to very short time in welding ,the cooling rate of the joint reaches to 5.1×106
K Πs ,the growth of austenite micro 2structure is im peded ,and the microstructure of the nugget is refined ,
which has rapidly s olidified characteristics.As the austenite micro 2structure of the nugget stays in tem perature province of activation with very short time ,the chrome of austenite grain boundary precipi 2tations is checked.T o obtain the high quality spot 2weld joint ,the welding parameters are determined as :welding v oltage 80V ,capac 2itor 6600μF and electrode pressure 18N.
K ey w ords : austenitic stainless steel ;capacitor discharge welding ;spot 2weld joint
Analysis for the influences of aluminum alloy P 2MIG w elding p arameters on w elding arc LU Zhiqiang 1,2
,H UA Xueming 1,2
,
LI Fang 1,2,W U Y ixiong 1,2
(1.Material and Science Engineering Department ,Shanghai Jiaotong University ,Shanghai 200240,Chi 2na ;2.The K ey Laboratory of Laser Processing and Material M odifi 2cation of Shanghai ,Shanghai 200240,China ).p 105-108
Abstract : Under the same average welding current and weld 2ing v oltage ,by regulating the different based current and peak cur 2rent ,the Al 2Mg alloy was welded with Al 2Mg filler wire.The photos of welding arc were obtained by using high 2speed video photography.Peak current has great in fluence on the shape and characteristics of the arc.With increasing the peak current value ,rotated arc appears and pulsed rotated metal trans fer behavior occurs.Based current has little in fluence on the arc shape.Base current is the im portant pa 2rameter for keeping arc burning.At pulse off time ,it must be given base current value which is large enough to keep the arc burning sta 2bly.In this study ,the arc shape is defined by arc length ,arc width and arc portrait cross 2section area ,which will be in fluenced by the weld current.Peak current is im portant parameter of arc tem perature and pulse energy.The study shows that when the arc is burning at pulse on time ,the arc length ,arc width and arc portrait cross 2sec 2tion area increase with raising peak current.
K ey w ords : aluminum alloy ;arc shape ;pulsed 2insert gas welding ;current
Welding technology and microstructure of MIG w elded m agne 2sium alloy W ANG Peng ,S ONG G ang ,LI U Liming (School of Materials Science and Engineering ,Dalian University of T echnology ,Dalian 116024,China ).p 109-112
Abstract : The pulsed MIG welding was used to weld AZ 31B Mg alloy ,and the weldability of the alloy was studied.The micro 2structure ,mechanical property and hardness of the welded joint were investigated via the metal phase microscopy ,scanning electron mi 2croscope ,tensile testing machine and hardness instrument.The re 2sults show that one 2side welding with back can be obtained through this technique at optimized parameters when there was no groove and no shaped ban ,which continuous butt joints have no sur face defects.The heat 2affected zone of the joints is narrow ,and the grains of the zone are slightly larger than that of the base metal.The grains of fu 2sion zone are tiny ,the microstructure is hom ogeneous and the hard 2ness of welded joint is higher than that of the base metal.The tensile strength is up to 95%of the base metal.
K ey w ords : pulsed MIGwelding ;magnesium alloy ;welding process ;microstructure
Ⅵ MAI N T OPICS ,ABSTRACTS &KEY W ORDS 2009,V ol.30,N o.12
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