X80管线钢闪光对焊热模拟试验

X80管线钢是目前应用最广泛的油气运输材料，因需满足长时间、长距离的服役条件，要求其具有更高的焊接性能，而闪光对焊技术由于焊接质量好、效率高，可满足X80管线钢的焊接需要。利用Gleeble-3800热模拟试验机对X80管线钢进行了闪光对焊模拟试验，采用金相显微镜观察焊缝、热影响区及母材处金相组织，采用显微维氏硬度计测定了各区硬度，确定了最优焊接参数。结果表明：在Gleeble热模拟试验机进行闪光对焊模拟试验，模拟焊接效果良好；不同工艺参数下焊接接头焊缝处金相组织为贝氏体，热影响区组织为贝氏体和铁素体，母材为铁素体和珠光体组织；不同焊接参数下，试样热影响区硬度最高，焊缝区次之，母材硬度最低；为获得优异的焊接接头，最优焊接参数为闪光速度1 mm/s、闪光流量6 mm。     

马弗用BSTMUF601厚板焊接接头的组织与性能试验研究

试验采用金相显微镜(OM)、洛氏硬度计及高温拉伸力学性能测试,定量分析光亮退火马弗用BSTMUF601厚板焊接接头组织特征、硬度分布及高温力学性能。结果表明,焊接热影响区组织过渡良好,焊缝区未见裂纹、气孔和夹杂等缺陷;马弗管的焊接工艺增强了原来母材材料的硬度指标;母材区与焊缝区均在1 100℃的条件下力学性能达到最优。通过对焊接工艺的可靠性进行评价,为低成本马弗管的国产化应用提供依据。     

QP980淬火-配分钢MAG焊接头组织及力学性能

QP980淬火-配分钢属于第三代先进高强钢，具有强塑积高、成形性好等优点而成为汽车轻量化发展的重要材料。对国内某公司生产的1.5 mm厚的QP980淬火-配分钢采用机器人MAG焊(熔化极活性气体保护焊)进行焊接，分析焊接工艺参数对其焊接接头组织和力学性能的影响。考虑到焊接的淬火作用以及焊接接头的等强匹配原则，采用ER50-6焊丝作为填充材料。研究结果表明，在合适的焊接工艺窗口内，减小焊接热输入有利于提高焊接接头的强度，但对其塑性有不利影响。焊接接头横截面的组织和力学性能变化非常大，焊缝金属区主要由铁素体和珠光体组成，硬度较低，但能达到原始母材的硬度值；靠近焊缝的热影响区主要是完全相变区，该区是由原始母材组织发生奥氏体转变后冷却产生的以板条马氏体为主的组织，硬度较母材有较大提升，该区成为焊接接头的硬化区，而靠近母材的焊接热影响区主要包括两相区和回火区，两相区中部分组织发生了奥氏体转变，冷却后转变的组织较原始组织中的马氏体含量有所降低，硬度略有下降，而回火区是由原始组织中的铁素体、少量奥氏体以及发生了回火的马氏体组成，由于马氏体的回火作用，硬度也略有降低。在该钢的MAG焊中，焊接接头软化现...     

TA19钛合金电子束焊接头微观组织与性能研究

采用电子束焊接方法对TA19钛合金进行焊接,分析了电子束焊接头各区域的显微组织类型及形貌,测试了接头的显微硬度、室温拉伸、疲劳裂纹扩展速率及断裂韧性等力学性能,并与TA19钛合金母材进行对比。研究表明,焊缝区为粗大的柱状晶组织并存在大量相互交错分布的针状马氏体相,热影响区内随着离熔合线距离的增加马氏体数量逐渐减少;焊缝区显微硬度最高,比母材区显微硬度高出约HV80,随着向母材区过渡显微硬度逐渐降低;焊接接头室温抗拉强度、屈服强度性能及断面收缩率均与母材基本相当,但延伸率略有下降;焊缝区粗大的柱状晶组织硬度高,脆性大,导致焊缝区对疲劳裂纹扩展的抗裂性要低于母材;母材及焊缝KIC值分别为54.49和52.88 MPa·m^1/2,母材抵抗裂纹扩展断裂的能力略好于焊缝。     

Ti60合金板材电子束焊接接头组织性能研究

研究了Ti60合金板材电子束焊接接头的显微组织与力学性能.研究表明,焊接接头熔合区中的显微组织由针状α′相、α相和β相组成,热影响区的显微组织为β相转变组织、针状α′相及部分未溶解的等轴初生α相组成的混合组织.焊接接头硬度呈不均匀分布,焊缝熔合区的硬度最高,热影响区次之,母材区最低.焊接接头的室温和高温拉伸均断裂于母材区,焊接接头处拉伸强度等同于接头处母材区的强度.焊接接头的持久断裂均发生于焊缝区域,接头的持久寿命均100 h.     

纯镍N6填丝等离子焊接工艺及接头组织性能的研究

试验采用等离子弧焊设备对工业纯镍N6板材进行填充焊丝等离子焊接工艺试验。借助光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)、X射线衍射仪(XRD)和显微硬度计等手段分析了焊接接头的微观组织和力学性能。结果表明:采用合理的焊接工艺参数可以得到成形良好的焊缝,填丝焊接接头抗拉强度为333 MPa,其抗拉强度达到母材强度的97.6%,不填丝焊接接头抗拉强度为240 MPa,达到母材强度的70.5%;母材为均匀细小的等轴晶,填丝接头焊缝处呈树枝状结晶且晶粒粗大,热影响区靠近熔池部分的晶粒过热长大,靠近母材部分为均匀细小的等轴晶;填丝接头基体为γ-Ni组织,同时存在γ'(Ni3(Al,Ti)C)强化相,填丝接头拉伸断口表现为韧-脆混合断裂,焊接接头硬度最低值出现在热影响区;与母材相比,不填丝接头焊缝区与热影响区晶粒粗大,其基体组织为单相奥氏体,不填丝接头拉伸断口表现为脆性断裂,硬度最低值出现在接头热影响区。     

电子束焊喷射成形Al-Zn-Mg-Cu合金的组织性能研究

采用电子束焊接的方法对10 mm厚的喷射成形Al-Zn-Mg-Cu合金板进行了拼焊实验。采用金相显微镜、扫描电镜、室温拉伸实验、显微硬度等方法分析了焊接接头的微观组织,测试了焊接接头的力学性能及显微硬度。结果表明,喷射成形Al-Zn-Mg-Cu合金焊接接头由三个区域(近缝区母材,焊核区,热影响区)组成。焊缝宽为0.3～1.0 mm,焊核区由尺寸约3～8μm的等轴细晶组成,析出相沿晶界分布,晶内析出相较少;热影响区大部分保留了母材的原始组织特征,小部分区域发生了重熔。从焊缝区到母材,显微硬度值逐渐下降,焊缝区硬度值高出母材约35。经T6处理后,焊接接头强度约为母材的82%。     

40CrNiMoA钢同质焊条焊接接头组织和性能研究

分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。     

热处理对40CrNiMoA钢板焊接接头组织及力学性能的影响

本文研究了调质工艺对40CrNiMoA钢板焊接接头显微组织及力学性能的影响。试验结果表明,经 830 - 870 °C +550 - 650 °C 调质处理后,40CrNiMoA钢3 mm板90 A 10 V焊接接头的焊缝区、热影响区、母材区的硬度差异显著减小,形成了回火索氏体组织。调质处理温度越高,焊接接头的焊缝区、热影响区与母材区的组织越 均匀,且组织中的碳化物颗粒尺寸增大。40CrNiMoA钢焊接板经850 Y油淬,600 X.回火后,具有较高的强度(905 MPa)和塑性(13. 5% ),综合力学性能最优。     

TA1中厚板电子束焊接头疲劳裂纹扩展速率研究

针对厚度为30 mm的TA1工业纯钛试板开展电子束焊接试验。通过对焊接接头的母材、热影响区和焊缝进行微观组织及维氏硬度测试,分析焊接过程对TA1材料组织及性能的影响。将疲劳裂纹扩展特性与接头各区域组织相结合,论述微观组织分布差异对焊接试样宏观裂纹扩展路径及裂纹扩展速率的影响。结果表明:与TA1母材相比,电子束焊接头焊缝及热影响区具有更高的疲劳裂纹扩展抗力,导致疲劳裂纹扩展路径发生偏折并最终偏向母材。与具有等轴α相的母材相比,电子束焊接过程中生成的锯齿α及α柱状晶对疲劳裂纹扩展具有阻碍作用。在应力比为0.1的试验条件下,焊缝处的疲劳裂纹扩展速率最低,热影响区其次,母材最高。     

Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

The Mechanisms of Resistance Spot Welding of Magnesium to Steel

Resistance spot welding of AZ31 magnesium alloys from different suppliers, AZ31-SA (from supplier A) and AZ31-SB (from supplier B), was studied and compared in this article. The mechanical properties and microstructures have been studied of welds made with a range of welding currents. For both groups of welds, the tension-shear fracture load (F _C) and fracture toughness (K _C) increased with the increase in welding current. The F _C and K _C of AZ31-SA welds were larger than those of AZ31-SB welds. The fracture surfaces of AZ31-SB welds were relatively flatter than those of AZ31-SA. Microstructural examination via optical microscope demonstrated that almost all weld nuggets comprised two different zones, the columnar dendritic zone (CDZ), which grew epitaxially from the fusion boundary, and the equiaxed dendritic zone (EDZ), which formed in the center of the nugget. The nature and extent of the CDZ seemed to be critical to the strength and toughness of spot welds because of its position adjacent to the inherent external circular crack-like notch of spot welds and the stress concentration in this region. The width and microstructure of the CDZ were different between AZ31-SA and AZ31-SB. The AZ31-SA alloy produced finer and shorter columnar dendrites, whereas the AZ31-SB alloy produced coarser and wider columnar dendrites. The width of the CDZ close to the notch decreased with the increase of current. The CDZ disappeared when the current was higher than a critical value, which was about 24 kA for AZ31-SA and 28 kA for AZ31-SB. The microhardness of the two base materials was the same, but within the CDZ and EDZ, the hardness was greater in AZ31-SA than AZ31-SB welds. It is believed that the different microstructures of spot welds between AZ31-SA and AZ31-SB resulted in different mechanical properties; in particular, K _C increased with the welding current because of the improved columnar-to-equiaxed transition.     

Statistic distribution characterization of compositions,microstructure and microhardness in surfacing area

The distribution characterization of compositions, microstructure and hardness in surfacing fusion zone of X80 pipeline steel was done by laser induced breakdown spectrum original position analyzer, automatic metallographic and micro Vickers hardness instruments. The results show that the content distributions are very different for some elements in the surfacing area. There is a cricoid enrichment zone of Ti in the fusion area of base metal and welding material, and significant change for the content distribution of C is not found. The microstructures in different fusion area are also very different. The grain is fine and there are a lot of strip ferrite and a little pearlite in the matrix organization of pipeline steel. In heat affected zone, recrystallization of the grain occurs and a large number of granular bainites appear. At the junction of weld melted metal, the grains get larger and a lot of lath martensites and bainites come into being. Vickers hardness of base metal is lower than welding material and a cricoid zone with higher Vickers hardness appeared in the fusion area. The micro- hardness distribution has close relationship with the composition distributions of the elements and microstructure distribution in welding area of pipeline steel.     

Resistance Spot Welded AZ31 Magnesium Alloys,Part II: Effects of Welding Current on Microstructure and Mechanical Properties

Resistance spot welding of AZ31 magnesium alloys from different suppliers, AZ31-SA (from supplier A) and AZ31-SB (from supplier B), was studied and compared in this article. The mechanical properties and microstructures have been studied of welds made with a range of welding currents. For both groups of welds, the tension-shear fracture load (F _C) and fracture toughness (K _C) increased with the increase in welding current. The F _C and K _C of AZ31-SA welds were larger than those of AZ31-SB welds. The fracture surfaces of AZ31-SB welds were relatively flatter than those of AZ31-SA. Microstructural examination via optical microscope demonstrated that almost all weld nuggets comprised two different zones, the columnar dendritic zone (CDZ), which grew epitaxially from the fusion boundary, and the equiaxed dendritic zone (EDZ), which formed in the center of the nugget. The nature and extent of the CDZ seemed to be critical to the strength and toughness of spot welds because of its position adjacent to the inherent external circular crack-like notch of spot welds and the stress concentration in this region. The width and microstructure of the CDZ were different between AZ31-SA and AZ31-SB. The AZ31-SA alloy produced finer and shorter columnar dendrites, whereas the AZ31-SB alloy produced coarser and wider columnar dendrites. The width of the CDZ close to the notch decreased with the increase of current. The CDZ disappeared when the current was higher than a critical value, which was about 24 kA for AZ31-SA and 28 kA for AZ31-SB. The microhardness of the two base materials was the same, but within the CDZ and EDZ, the hardness was greater in AZ31-SA than AZ31-SB welds. It is believed that the different microstructures of spot welds between AZ31-SA and AZ31-SB resulted in different mechanical properties; in particular, K _C increased with the welding current because of the improved columnar-to-equiaxed transition.     

Laser Keyhole Welding of Dissimilar Ti-6Al-4V Titanium Alloy to AZ31B Magnesium Alloy

Laser keyhole welding of Ti-6Al-4V titanium alloy to AZ31B magnesium alloy was developed, and the correlations of process parameters, joint properties, and bonding mechanism were studied. The results show that the offset from the laser beam center on AZ31B side to the edge of the weld seam plays a big role in the joint properties by changing the power density irradiated at the Ti–Mg initial interface. The optimal range of the offset is 0.3 to 0.4mm in the present study. Some lamellar and granular Ti-rich mixtures are observed in the fusion zone, which is formed by intermixing melted Ti-6Al-4V with liquid AZ31B. The maximum ultimate tensile strength of the joints reaches 266 MPa. Furthermore, the fracture surface consists of scraggly remaining weld metal and smooth Ti surface. The higher the failure strength, the smaller the proportion of smooth Ti surface to whole interface is. Finally, the bonding mechanism of the interfacial layer is summarized by the morphologies and test results of fracture surfaces.     

Microstructure and Fatigue Properties of a Friction Stir Lap Welded Magnesium Alloy

Friction stir welding (FSW), being an enabling solid-state joining technology, can be suitably applied for the assembly of lightweight magnesium (Mg) alloys. In this investigation, friction stir lap welded (FSLWed) joints of AZ31B-H24 Mg alloy were characterized in terms of the welding defects, microstructure, hardness, and fatigue properties at various combinations of tool rotational rates and welding speeds. It was observed that the hardness decreased from the base metal (BM) to the stir zone (SZ) across the heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ). The lowest value of hardness appeared in the SZ. With increasing tool rotational rate or decreasing welding speed, the average hardness in the SZ decreased owing to increasing grain size, and a Hall–Petch-type relationship was established. Fatigue fracture of the lap welds always occurred at the interface between the SZ and TMAZ on the advancing side where a larger hooking defect was present (in comparison with the retreating side). The welding parameters had a significant influence on the hook height and the subsequent fatigue life. A relatively “cold” weld, conducted at a rotational rate of 1000 rpm and welding speed of 20 mm/s, gave rise to almost complete elimination of the hooking defect, thus considerably (over two orders of magnitude) improving the fatigue life. Fatigue crack propagation was basically characterized by the formation of fatigue striations concomitantly with secondary cracks.     

焊接电流对镁/镀锌钢 TIG熔--钎焊接头显微组织与力学性能的影响

采用TIG熔-钎焊焊接方法,以镁合金焊丝为填充材料,对镁合金与镀锌钢进行连接实验,并分析热输入量对接头显微组织和力学性能的影响.热输入量过小会阻碍镁/钢界面反应层的形成而使得焊缝难以焊合,热输入量过大又会促进焊缝内部脆性第二相的长大,降低接头力学性能.接头强度随着焊接电流和焊接速度的增大都呈现先上升后下降的趋势,电流为70 A时强度达到最大,该值接近AZ31B母材的88.7%.此时断裂发生于焊缝熔焊区,断面出现大量韧窝和撕裂棱,呈现出塑性断裂特征.      

焊接速度对机器人搅拌摩擦焊AA7B04铝合金接头组织和力学性能的影响

针对熔化焊在焊接AA7B04铝合金时易在焊缝中出现孔洞等缺陷,且接头性能下降明显、焊后变形大,以及采用铆接等机械连接方式会增加连接件的重量等问题,采用集成了搅拌摩擦焊末端执行器的KUKA Titan机器人对2 mm厚AA7B04高强铝合金进行了焊接,在转速为800 r·min-1的条件下,研究了焊度对焊接过程中搅拌头3个方向的受力F_x、F_y和F_z的影响.研究发现,F_z受焊速的影响显著,随焊速的增加而降低.利用光学显微镜、透射电子显微镜、拉伸试验、三点弯曲试验和硬度测试等方法,研究了不同焊速下AA7B04铝合金接头的微观组织和力学性能.结果表明:当焊速为100 mm·min-1时,接头的抗拉强度最高为447 MPa,可达母材的80%,且所有接头的正弯和背弯180°均无裂纹;接头横截面的硬度分布呈W型,硬度最低点出现在热力影响区和焊核区的交界处,焊速不同会导致不同的焊接热循环,且随着焊速的增加接头的硬度随之增加;焊核区组织发生了动态再结晶,生成了细小的等轴晶粒,前进侧和后退侧热力影响区的晶粒均发生了明显的变形;前进侧热影响区析出η'相,后退侧热影响区因温度较高析出η'相和尺寸较大的η相.      

7003铝合金TIG焊焊接接头的组织与性能

采用显微硬度及电导率测试,剥落腐蚀及电化学腐蚀试验,光学显微镜(OM)及透射电镜(TEM),研究经ER5356焊丝钨极氩弧焊(TIG)的7003铝合金型材焊接接头各部分的微观组织与性能。结果表明:在离焊缝中心30 mm左右的热影响区位置形成硬度较低的软化区,这是由于η′(Mg Zn2)相的长大粗化;焊接接头的耐蚀性依次为焊缝区过时效区母材区淬火区,其原因是淬火区的晶界析出相连续分布,形成连续阳极腐蚀通道,增大了应力腐蚀及剥落腐蚀倾向,使得腐蚀性能很差;而过时效区和母材区的晶界析出相不连续,耐蚀性较好。     

Cold Metal Transfer Welding of Dissimilar A6061 Aluminium Alloy-AZ31B Magnesium Alloy: Effect of Heat Input on Microstructure,Residual Stress and Corrosion Behavior

Lap joints of aluminum alloy A6061-T6 and AZ31B magnesium alloy were produced by cold metal transfer welding with Al-5 %Si filler metal. Four heat inputs designated as A (175 J/mm), B (185 J/mm), C (195 J/mm) and D (205 J/mm) were used during the process and the joints made were subjected to analysis of microstructure, mechanical properties and corrosion behaviour. The thickness of the fusion line (diffusion layer) varied from 3 to 12 µm depending on the heat input. It was also found that the joints made using the heat input of 205 J/mm exhibited highest tensile strength of 360 N/mm, least tensile stress in the weld and better pitting corrosion resistance. Electron microscopy study of the weld revealed the presence of β′-Mg₂Si, Al₆Mn and β-Al₃Mg₂ particles. X-ray diffraction study in the weld revealed the formation of γ-Al₁₂Mg₁₇ and β-Al₃Mg₂ phase with Mg₂Si strengthening precipitates. Tensile failure occurred at the fusion line near magnesium.