气孔对铝合金焊接接头超长疲劳寿命的影响

第35卷第11期2014年11月

焊接学报

TＲANSACTIONS OF THE CHINA WELDING INSTITUTION

Vol．35No．11November

2014

收稿日期：2013－04－24

基金项目：国家自然科学基金资助项目（10772125；10372064）

气孔对铝合金焊接接头超长疲劳寿命的影响

何

超，崔仕明，刘永杰，王清远

（四川大学能源工程安全与灾害力学教育部重点实验室，成都610065）

摘

要：采用超声疲劳试验方法对铝合金5052-H32焊接接头进行疲劳试验，研究其在超长寿命区间（107 109

周

次）的疲劳强度及失效机理．结果表明，相同疲劳寿命下焊接接头疲劳强度较母材下降了73．3%，在超高周疲劳区间仍然会发生疲劳破坏；断口观察发现焊接缺陷（气孔）是诱发疲劳裂纹萌生的主要原因．为揭示焊接缺陷对焊接接头疲劳裂纹萌生及扩展的影响，采用有限元技术分析了气孔对应力集中系数和裂纹尖端应力强度因子的影响．最后讨论了焊接缺陷对疲劳寿命的影响机制及裂纹扩展特性．关键词：焊接接头；铝合金；超高周疲劳；气孔；应力强度因子中图分类号：O 346．2；TG 405

文献标识码：A

文章编号：0253－360X （2014）11－0018－05

0序言

许多工程结构和机械部件（车轴、近海平台、桥

梁等）在其服役期内往往承受超过1?1010

周次循环

载荷的作用［1］

，而焊接接头作为结构件广泛使用的连接方式，由于其力学性能和组织的不均匀性经常

发生疲劳失效现象，成为结构使用过程中的疲劳危

险点［2］．因而常规疲劳试验（小于1?107

周次）所获得的疲劳极限、疲劳强度等材料参数通常不能进行推广应用于低应力作用下的超长寿命疲劳设计．

因此，研究焊接接头超高周疲劳行为（1?107

1?109周次）对于材料的安全使用具有重要意义．

超声疲劳试验系统的发展使材料的超高疲劳行

为研究成为热点，

对高强度钢、钛合金以及铝合金的研究发现

［3，4］

，通常材料不存在传统疲劳极限，低应

力循环荷载作用下同样会发生疲劳破坏．对于焊接接头的超高周疲劳问题，方冬慧等人［5］

发现桥梁钢焊接接头的超高周疲劳性能远低于母材；Yin 等人

［6］

发现超长寿命区间内低合金钢焊接接头存在疲劳极限，超声冲击处理可以明显改善焊接接头的疲劳性能；Zhu 等人［7］

研究了高温下焊接接头的超高周疲劳行为，发现基体软化、表面氧化和残余应力是导致疲劳裂纹萌生的主要原因．目前已有的研究发现焊接接头疲劳性能降低主要由内部焊接缺陷所致，但缺陷（如气孔、微裂等）对疲劳裂纹萌生及扩展机理的详细阐述仍不明确．

文中将对5052铝合金焊接接头的超高周疲劳

寿命进行试验研究，探究其在低应力循环作用下的疲劳失效机理；利用有限元分析了气孔对孔边应力集中系统和裂纹尖端应力强度因子的影响，进而讨论焊接缺陷诱发疲劳裂纹萌生的机制及裂纹扩展特性．

1试验方法

采用材料为铝合金5052-H32，力学性能及化学

组成成分如表1和表2所示．采用钨极氩弧焊方法将两块厚度为5mm 的平板进行对接，试样由对接平板焊缝处利用电火花线切割加工得到（图1a ），共振疲劳试验要求试样轴向一阶固有频率与系统相同（20kHz ），为此试样几何尺寸必须进行严格的计算，为减小圆弧根部的应力集中效应，试样中间加入6

mm 的等截面段，具体尺寸如图1b 所示，采用砂纸由粗到细对试样表面逐级进行打磨，

去除焊接余高，消除表面几何条件不均匀性对疲劳性能的影响，并且

最后进行电解抛光，减少表面缺陷对疲劳裂纹萌生的影响．

表1

5052铝合金力学性能

Table 1

Mechanical properties of 5052-H32aluminium

alloy

弹性模量E /GPa

屈服强度ＲeL /MPa 抗拉强度Ｒm /MPa 维氏硬度H HV /MPa 断后伸长率A （%）70．3

195

223

64

12

第11期

何超，等：气孔对铝合金焊接接头超长疲劳寿命的影响

19

表25052铝合金化学组成成分（质量分数，%）Table 2

Chemical compositions of 5052-H32aluminium alloy

Al Cr Cu Fe Mg Mn Si Zn 96．1

0．15

0．08

0．33

2．41

0．09

0．21

0．

07

图1

超声疲劳试样设计

Fig.1

Dimensions of fatigue specimen

试验采用USF-2000超声疲劳试验系统，加载频

率为20kHz ，应力比Ｒ=－1．试验进行过程中，最高应力出现在试样中间最小截面处，通过对试样端部振动位移的控制实现不同应力水平的加载，详细原

理可参见文献［

8］．为防止高频加载下温度升高对疲劳性能测定带来的影响，采用经干燥制冷（4?）

的压缩空气（0．1MPa ）对试样表面进行冷却．

2

试验结果

2．2

疲劳S-N 数据分析铝合金5052焊接接头（圆形）及母材（正方形）

超声疲劳试验所得S-N 数据如图2所示，箭头所示

数据点表示该试样疲劳寿命达到1?109

周次仍未断裂．数据显示铝合金母材及焊接接头疲劳强度均

呈现连续下降趋势，随着疲劳寿命的增加，疲劳强度

越低，

1?107周次后仍然会有疲劳破坏发生，1?109周次以内不存在疲劳极限．同时可以看到，疲劳寿

命同为1?109

周次时，焊接接头所能承受的最大加

载应力（40MPa ）仅为母材（150MPa ）的26．7%，焊接接头超高周疲劳强度远低于母材，相似结论在Q235，Q345以及Ti-6Al-4V 焊接接头的超高周疲劳试验中同样得以证实［5］

．因此在进行承受超长寿命结构及部件的设计时，焊接接头对整体疲劳性能的劣化影响应予以特别重视

．

图2

铝合金母材及焊接接头疲劳试验数据

Fig.2

Fatigue data of base metal and welded joint speci-men for aluminium alloy

2．3

断口形貌及裂纹萌生机理试验结果发现，焊接接头疲劳断裂通常发生在

焊缝区，热影响区的软化并没有导致疲劳强度的降低，

Chai ［9

］通过双相不锈钢的超声疲劳试验发现，在低应力水平加载下，试样整体呈现弹性变形，但由于组织的不均匀性，微塑性仍然在局部区域的弱相存在，并由此引发疲劳裂纹的萌生，导致破坏．由此说明，对于铝合金焊接接头超长疲劳寿命问题，由于焊接过程引入大量的缺陷以及组织的不均匀性，焊缝区相比其它区域存在更多的微塑性区，使焊接接头疲劳破坏在此产生．

为了探究铝合金焊接接头疲劳断裂机理，采用扫描电镜对试样断口表面形貌进行分析．图3所示为60MPa 应力加载下疲劳断口形貌，

可以看到整个

图3

焊接接头超高周疲劳断裂的断口特征

Fig.3

Fractography of welded joint in ouper high cycle fatigue

20焊接学报第35卷

裂纹扩展面主要分为两个区域（图3a ），区域I 断口表面相比区域II 更平坦，这是由于疲劳裂纹扩展初期速率较低，相同时间下承受的循环加载次数更多，裂纹面相互挤压形成的．疲劳裂纹从位于试样次表面的气孔处萌生（图3b ），而试样内部气孔并没有诱发疲劳裂纹萌生，但会引起裂纹扩展路径的改变，使裂纹贯穿气孔进行扩展（图3c ）．

对所有发生疲劳断裂的试样断口表面进行SEM 分析，发现疲劳裂纹通常由位于表面或次表面的气孔处开始扩展，导致最终的断裂，如图4所示．同时发现不同疲劳寿命下，裂纹起源处气孔直径也

随之不同，

为更深入探究这两者之间的联系，对1?106 1?109周次发性疲劳断裂的试样气孔直径进行测量，结果如图5所示，随着疲劳寿命的增加，引起疲劳裂纹扩展的气孔直径越小．值得注意的是，对于内部含夹杂物的高强度钢，大量研究［1］

发现夹杂物尺寸与材料疲劳寿命有着密切联系，甚至基于裂纹源处非金属夹杂物尺寸，

提出了预测材料超长疲劳寿命的经验公式．因此可以看出，无论是高强度钢或焊接接头，内部缺陷对材料超周疲劳寿命有着至关重要的作用，而焊接接头中气孔对疲劳寿命的影响机理，后面章节将进行详细介绍

．

图4

SEM 观察下的疲劳裂纹萌生源

Fig.4

Fatigue crack initiation sites from SEM

observation

图5不同寿命下裂纹起源处气孔直径大小的分布

Fig.5

Profiles of pore diameters with different fatigue lives

3

气孔对超高周疲劳裂纹的影响

3．1

气孔大小对疲劳裂纹萌生的影响

对于不含夹杂物的金属材料，

Mughrabi ［10］提出，

低周疲劳时由于加载应力较高，表面局部区域由于组织不均匀性使一些晶粒进入塑性形成滑移，从而使试样表面变化得粗糙不平，应力加载下产生应力集中效应，由此又加剧滑移带的形成，一定循环加载周次后裂纹便由表面形成；进入高周及超高疲劳后，较低的加载应力已经不足以使表面形成足够的滑移带形成裂纹，因此疲劳裂纹起源会由表面转移

到内部，经历相当长的循环加载以后，内部夹杂物与基体界面发生脱离，裂纹便由此开始扩展，并在夹杂物周围形成相对粗糙的区域，

称为光学暗区（ODA ）．试验中铝合金接头疲劳裂纹萌生机理与高强度钢有相似但又有自己的特点．首先疲劳裂纹均起源于试样内部或次表面的气孔，与高强度裂纹从内部夹杂起源形象类似；其次由于气孔的存在导致试样内部几何条件不连续，孔边出现应力集中现象，使孔边应力远高于外部加载应力，滑移带更容易在

孔边出现，萌生疲劳裂纹（图6），这又类似于高强度钢表面裂纹萌生方式，不同的是高强度钢是由于微观组织不连续导致晶粒间应力分布不均匀，而铝合金焊接接头则是由于几何条件的不连续造成的．

由前面的讨论可知，孔边的应力集中造成高应力区的出现，最终裂纹由此处的滑移带萌生．应力越高，疲劳裂纹越容易出现，疲劳寿命越短．为了简要说明气孔的大小将会影响到孔边应力分布的影响，

利用ANSYS 求解拉伸载荷作用下有限宽板偏心圆孔的应力集中问题（图7），模型下部施加y 方向自由度约束，承受50MPa 拉伸应力，圆孔半径为Ｒ，圆心与表面距离为D ，通过计算不同圆孔半径Ｒ和表面距离D 比值下的应力集中系数，所得结果如图8所示，发现随着Ｒ的增大，圆孔边缘应力集中系

第11期何超，等：气孔对铝合金焊接接头超长疲劳寿命的影响

21

图6

孔边滑移带诱发疲劳裂纹萌生

Fig.6

Fatigue crack initiation caused by slip band at sur-face of pore

数也同样增大，相同远端加载应力下孔边应力也越大，也就解释了疲劳寿命越长，引起疲劳裂纹扩展的气孔直径也越大的原因．同时发现圆孔半径Ｒ一定时，圆孔与表面距离D 越小，应力集中系数也越大，说明位于近表面的气孔比处于内部的气孔更容易萌生疲劳裂纹，这也是断口分析中诱发裂纹起源的气孔基本都处于次表面的原因

．

图7拉伸偏心圆孔板

Fig.7

Tension strip with biasly located circular

hole

图8圆孔半径及表面距离对应力集中系数的影响Fig.8

Influence of Ｒand D on stress intensity factor

3．2

气孔对疲劳裂纹扩展速率的影响疲劳裂纹自孔边萌生以后，将沿着与加载应力

方向垂直的平面扩展，气孔的存在将影响到裂纹尖端应力强度因子的大小，从而影响到疲劳裂纹扩展速率．目前求解应力强度因子的方法中，解析法只

能到得几何条件相对简单的情况，而更加复杂的三

维模型往往只能采用数值方法求解近似值．对于三维孔边裂纹问题，文中采用有限元方法进行求解，如图9所示，为减少计算时间，采用只对模型的1/4进行建模，长度为a 的平面裂纹位于无限大体内（实际计算采用值大于20倍裂纹长度），裂纹尖端采用1/4节点奇异单元进行网格划分，通过计算奇异单元1/4处节点的位移便可求得应力强度因子值．相

同裂纹长度下，分别计算元气孔（图9a ）和含有气孔（图9b ）两种情况的应力强度因子值

．

图9三维应力强度因子计算模型

Fig.93D model for stress intensity factor

通过计算得到不同裂纹长度和气孔半径下应力强度因子的变化情况（图10）．可以看到随着疲劳裂纹的扩展，

气孔对应力强度因子的影响经历先减弱后增强的阶段：裂纹长度与气孔半径之比a /Ｒ小于1．3时，含有气孔的裂纹应力强度因子值将小于无气孔裂纹；疲劳裂纹扩展到气孔半径的1．5倍时，

气孔对应力强度因子的影响达到最大；当疲劳裂纹长度大于气孔半径的3．5倍后，这种影响可忽略不计

．

图10气孔对应力强度因子的影响

Fig.10Influence of pore on stress intense factor

3．3

气孔对疲劳寿命的影响机理

超高强度钢等材料在超高周疲劳区间，疲劳裂

纹通常起源于内部，并呈现鱼眼特征或无夹杂内部

22焊接学报第35卷

起源形式［10］．王清远［1］研究发现鱼眼的形成寿命占疲劳总寿命的99%以上，疲劳裂纹扩展寿命相比萌生寿命只是很小一部分，疲劳裂纹从夹杂物萌生到扩展阶段需要超长时间的循环载荷作用．而对于文中焊接接头，疲劳裂纹源气孔的存在导致鱼眼形式的缺失，疲劳裂纹从气孔内表面萌生，可作为表面裂纹萌生的另一种形式，而气孔附近由于几何不连续存在应力集中现象，使孔边区域循环加载应力远高于实际施加荷载．综上所述，焊接接头由于内部气孔的存在，导致其疲劳寿命相比母材有大幅降低．

4结论

（1）铝合金焊接接头疲劳S-N曲线呈连续下降性，107周次后不存在疲劳极限；相同疲劳寿命下，焊接接头疲劳强度远低于母材，109周次时疲劳强度下降了73．3%．

（2）试样疲劳断裂均发生在焊缝区，热影响区的软化现象并不会诱发疲劳裂纹；焊缝区内部存在的气孔成为主要的疲劳裂纹萌生源，寿命越短，裂纹起源处的气孔直径越大．

（3）焊接接头疲劳裂纹萌生主要受气孔周边区域应力集中系数的影响，气孔直径越大，距离表面越近，造成的应力集中越明显；随着疲劳裂纹长度的增加，气孔对其尖端的应力强度因子影响呈现由减小到增大变化的趋势，裂纹长度超过气孔半径的3．5倍时，这种影响可以忽略．

（4）焊接接头疲劳寿命的降低主要是因为疲劳裂纹直接从气孔内表面萌生扩展，导致萌生寿命远低于母材．

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［5］方冬慧，刘永杰，陈宜言，等．Q345桥梁钢焊接接头超高周疲劳性能［J］．焊接学报，2011，32（8）：77－81．

Fang Donghui，Liu Yujie，Chen Yiyan，et al．Ultra-high cycle

fatigue behaviors of Q345bridge steel welded joint［J］．Transac-

tions of the China Welding Institution，2011，32（8）：77－81．［6］Yin D，Wang D，Jing H，et al．The effects of ultrasonic peening treatment on the ultra-long life fatigue behavior of welded joints

［J］．Materials＆amp；Design，2010，31（7）：3299－3307．［7］Zhu M L，Xuan F Z，Du Y N，et al．Very high cycle fatigue be-havior of a low strength welded joint at moderate temperature［J］．

International Journal of Fatigue，2012，40（7）：74－83．

［8］Bathias C．Piezo-electric fatigue testing machines and devices ［C］∥In：Sakai T，Ochi Y．editors．VHCF-3，Proc of the

Third Intern Conf on Very High Cycle Fatigue，2004：472－83．［9］Chai G C．Fatigue behaviour of duplex stainless steels in the very high cycle regime［J］．International Journal of Fatigue，2006，28

（11）：1611－1617．

［10］Mughrabi H．Specific features and mechanisms of fatigue in the ultrahigh-cycle regime［J］．International Journal of Fatigue，

2006，28（11）：1501－1508．

作者简介：何超，男，1986年出生，博士研究生．主要从事新型材料的力学行为方面的科研工作．发表论文10余篇．Email：hechaoscu@foxmail．com

通讯作者：王清远，男，教授．Email：wangqy@scu．edu．cn

2014，Vol．35，No．11TＲANSACTIONS OF THE CHINA WELDING INSTITUTION

MAIN TOPICS，ABSTＲACTS＆KEY WOＲDS

Arc behavior of A-MIG welding and microstructure of alu-minum alloy welded joint LU Hao1，XING Liwei1，LIANG Zhimin2（1．Technique Headquarters，CSＲQingdao Sifang CO．LTD．，Qingdao266111，China；2．Faculty of Material Science and Engineering，Hebei University of Science and Technology，Shijiazhuang054300，China）．pp1－4

Abstract：A new welding method-activating flux MIG（A-MIG）welding was proposed in this paper，which can obtain wel-ded joint with high quality and reduce lack of fusion．The arc morphology during this welding method were collected and ana-lyzed．The results show that the current density in A-MIG weld-ing was higher than that in conventional MIG welding．Based on the analysis with scanning electron microscope and transmission electron microscope，the inspection results by comparing A-MIG welding and conventional MIG welding show that the addition of activating flux did not affect precipitated phases and distribution of Mn，Cr and Ti alloying elements．

Key words：activating flux MIG welding；aluminum al-loy；arc morphology；microstructure

TGO growth of high temperature thermal barrier coatings HAN Zhiyong，WANG Xiaomei，WANG Zhiping（Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance，Civil Aviation University of China，Tianjin300300，China）．pp 5－8

Abstract：Growth mechanism of thermally growth oxide （TGO）in thermal barrier coatings（TBCs）was investigated by finite element analysis software ABAQUS．After high temperature oxidation for100hours，the thickness of TGO increased from0.5μm to6．7μm．With the increasing of high temperature oxida-tion，stresses in the peaks，valleys and interface of TGO were obviously larger than in other places．Meanwhile，cracks were prone to initiate and propagate at these locations，and eventually led to spalling of the entire coating．During high temperature oxi-dization，the total absorbed energy of coating was43．6J，some of which was consumed for coating deformation，and the remai-ning for changes of coating composition and microstructure，and crack propagation．

Key words：thermal barrier coating；thermally growth ox-ide；finite element software ABAQUS

Numerical simulation of temperature field in weaving weld-ing based on ladder model ZONG Xuemei，WU Bin，ZHANG Liping，LI Wen（Jiangsu Xuzhou ConstructionＲesearch Institute，Xuzhou Construction Machinery Group，Xuzhou 221004，China）．pp9－12

Abstract：According to the characteristic of weaving welding，an arc swing ladder model was established on basis of strip heat source and numerical simulation of temperature field in Q345steel plate butt joint with weaving welding was done using commercial software SYSWELD．The transient temperature field and thermal cycle curves in the welded zone were obtained．The results showed that the transient temperature field with arc-wea-ving ladder model was different from that with strip heat source model，and the weld pool with ladder model was elliptical with small head and big rump when the heat source moved from the middle to both sides．The thermal cycle curves with ladder model were also different from those with strip heat source model，and they had a wave crest both in heating and cooling，which reflec-ted that the weld was affected by the arc weaving upon heating and cooling．

Key words：weaving welding；ladder model；numerical simulation；temperature field

Effect of peak temperature and cooling rate in welding ther-mal cycle on microstructure and properties of CGHAZ in SA508-3steel L Xiaochun1，2，HE Peng1，QIN Jian2，DU Bing2，HU Zhongquan3（1．State Key Laboratory of Advanced Welding and Joining，Harbin Institute of Technology，Harbin 150001，China；2．Harbin Welding Institute，Harbin150028，China；3．Department of Mechanical Engineering，Tsinghua U-niversity，Beijing100084，China）．pp13－17

Abstract：Because the microhardness and absorbed ener-gy change greatly after CGHAZ experienceing different peak tem-perature and cooling rate in welding thermal cycle，the CGHAZ in the SA508-3steel joint is highly unstable．When the peak temperature in the second welding thermal cycle was600－700?，the CGHAZ could get a better match between hardness and toughness．The formation of hidden martensite near grain bound-ary and grain coarsening should be avoided after the CGHAZ ex-perienced secondary welding thermal cycle which peak tempera-ture was750－950?and t

8/5

was10s．

Key words：SA508-3steel；coarse grain heat-affected zone；peak temperature；cooling rate

Effect of pore on super long fatigue life of aluminium alloy welded joint HE Chao，CUI Shiming，LIU Yongjie，WANG Qingyuan（Key Laboratory of Energy Engineering Safety and Dis-aster Mechanics，Ministry of Education，Sichuan University，Chengdu610065，China）．pp18－22

Abstract：In order to investigate the fatigue behavior and failure mechanism in super long life regime，ultrasonic fatigue tests were performed on5052aluminium alloy welded joint．The results show that the fatigue strength of welded joint descended a-bout73．3%as compared to the base metal with the same fatigue life．Fatigue failure occurred in the very high cycle fatigue re-gime．Fatigue crack initiated from the welding defects（pores）from the observation of SEM．To clarify the effect of pores on the

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MAIN TOPICS，ABSTＲACTS＆KEY WOＲDS2014，Vol．35，No．11

crack initiation and propagation of welded joint，finite element method was used to calculate the stress concentration and stress intensity factor around the pores．Finally，the characteristics of fatigue crack initiation and propagation with welding defects were discussed．

Key words：welded joint；aluminium alloy；super high cycle fatigue；pore；stress intensity factor

Effect of laser power on arc behavior and metal transfer in laser-twin-wire pulsed MIG hybrid welding process ZHANG Xiaofeng1，LI Huan1，YANG Lijun1，GAO Ying2（1．Tianjin Key Laboratory of Joining Technology，Tianjin Universi-ty，Tianjin300072，China；2．Tianjin Key Laboratory of High-speed Cutting＆Precision Machining，Tianjin Vocational and Technical Normal University，Tianjin300222，China）．pp23－26，62

Abstract：Laser-twin-wire pulsed MIG hybrid welding is a new welding technology which combines laser welding and twin-wire MIG welding．As one of the most important factors in this technology，laser power has significant effect on the welding pro-cedure and properties of joint．A laser-twin-wire pulsed MIG hy-brid welding system was established to investigate the effect of la-ser power on arc behavior and metal transfer in this process．High-speed photography system with synchronous electrical sig-nal，including current and voltage signals，were adopted to re-cord the arc behavior and metal transfer during welding．The re-sults showed that the arc shape and stress status of the droplet were affected by the interaction between laser-induced plasma and arc plasma．With the increase of laser power，the laser-arc attraction was enhanced，the component force of plasma stream force in the vertical downward which could promote droplet trans-fer reduced．As a result，the droplet transfer frequency de-creased．

Key words：laser-twin-wire pulsed MIG hybrid welding；metal transfer；arc behavior；high-speed photography

Morphology of molten pool based on shadow during high-power laser deep penetration welding ZHANG Yanxi，GAO Xiangdong（School of Electromechanical Engineering，Guangdong University of Technology，Guangzhou510006，Chi-na）．pp27－30

Abstract：The morphology of molten pool，especially the volume of molten pool can not be measured directly by the cur-rent measurement methods．In this study，surfacing welding of thick304stainless steel plate with high-power disk laser welding was conducted．With extra auxiliary infrared laser light and high-speed camera，clear images of the molten pools and their shad-ows were obtained，and then the shadow area of molten pool was extracted to be analyzed by one-dimensional linear regression e-quation and correlation coefficient analysis method．The experi-mental results confirmed that the shadow area variation of molten pool had positive correlation with welding quality，and this pro-vided a new method for test of welding quality．

Key words：high-power disk laser welding；shadow of molten pool；morphology of molten pool；welding quality Activating brazing of Gr/2024Al composite material to TC4

titanium alloy with Ag-Cu-Sn-Ti filler SHI Junmiao1，ZHANG Lixia1，LI Hongwei1，TIAN Xiaoyu1，FENG Jicai1，2（1．State Key Laboratory of Advanced Welding and Joining，Harbin Institute of Technology，Harbin150001，China；2．Shandong Provincial Key Laboratory of Special Welding Technology，Har-bin Institute of Technology，Weihai264209，China）．pp31－34，38

Abstract：Gr/2024Al composite material and TC4titani-um alloy were successfully brazed with self-developed Ag-Cu-Sn-Ti filler alloy，and the interfacial microstructure and mechanical properties of the brazed joints were investigated．The results show that the typical interfacial structure of brazed joint was Gr/ 2024Al composite material/Ti

3

AlC

2

/Ag

2

Al+Ag

3

Sn+Al

2

Cu+

Al

5

CuTi

2

/Al

5

CuTi

2

/TC

4

titanium alloy．With the increasing of brazing temperature and extending of dwelling time，the amount

of Al2Cu compounds decreased but the amount of Al

5

CuTi

2

in-creased and it finally grew into bulk in the brazed seam．While brazed at953K for10min，the joint obtained maximum shear strength of17MPa at room temperature．

Key words：Gr/2024Al composite material；TC4；Ag-Cu-Sn-Ti filler；interfacial microstructure；shear strength Weldability of dissimilar steels for high-end cutting tools with A-TIG welding YIN Yan1，LIU Zhao1，SUN Peng1，ZHANGＲuihua2，LI Jihui3（1．State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials，Lanzhou University of Technology，Lanzhou730050，China；2．China Iron＆Steel Ｒesearch Institute Group，Beijing100081，China；3．Yang Jiang ShiBaZi Group，Yangjiang529500，China）．pp35－38 Abstract：In TIG welding of high-end cutting tools，the entire tools must be preheated．A-TIG welding was selected in this paper to weld430stainless steel knife back and sandwich （3Cr13-1Cr17-3Cr13）stainless steel blade，and study the effect of fluxes on the weld shape．The differences between A-TIG and conventional TIG on the weld penetration，pores in the weld，mi-crostructure，mechanical properties and corrosion resistance of the joint were studied in this paper．The results show that satis-fied joint with excellent weld appearance between430stainless steel knife back and sandwich（3Cr13-1Cr17-3Cr13）stainless steel blade could be achieved by A-TIG welding．No defects were detected in the joint and the grains in weld were refined．The HAZ was very narrow and the tensile strength of joint was606 MPa．The activating flux did not reduce the corrosion resistance of welded joint．

Key words：A-TIG welding；dissimilar steels；micro-structure；mechanical property

Effect of detonation velocity on interface and properties of Al/Ti composite tube under explosive welding DENG Wei1，2，LU Ming2，XU Qian2（1．63981Unite of PLA，Wuhan 430311，China；2．College of Field Engineering，PLA Univ．of Sci．＆Tech．，Nanjing210007，China）．pp39－42

Abstract：To obtain low detonation velocity explosive，commercial attenuant was blended into the emulsion explosive．

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