Microstructural investigation of friction stir welded 7050-T651 aluminium

The grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal. The various regions were studied in detail to better understand the microstructural evolution during friction stir welding (FSW). The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Using the combination of structural characteristics observed in each weld region, a new dynamic recrystallization model has been proposed. The precipitation phenomena in different weld regions are also discussed.     

激光焊接异种钢组织及显微硬度分析

采用激光摆动焊接方法焊接异种钢，利用JMATPro软件计算了母材3Cr13，VG10的平衡相图，通过XRD，SEM，EPMA等技术分别对焊缝、熔合区、热影响区的相组成和显微组织进行了分析，测定了焊接接头的显微硬度分布. 试验结果表明，焊缝主要为α相和碳化物M₇C₃；从熔合线到焊缝中心，组织由平面晶逐渐变为胞状晶、胞状树枝晶、树枝状晶、柱状晶、等轴晶. 焊缝组织存在显微偏析，其中C，Cr元素在晶界富集，Fe元素在晶内富集，同时在晶界处有条棒状的M₇C₃析出. 熔合线附近的母材处有C迁移现象，其中3Cr13侧母材处有类针状马氏体组织产生，VG10侧熔合区存在非对流混合区，在该位置有块状、岛状组织嵌入母材，且在该组织上有片层状的碳化物生成. 熔合线两侧的母材硬度值最大，焊缝区硬度变化较小，热影响区硬度随着远离焊缝中心距离的增加而逐渐减少.     

紫外光对铝合金焊接接头腐蚀行为的影响

通过光学显微镜分析研究了6061铝合金熔化极惰性气体保护焊(metal inter gas welding, MIG焊)和搅拌摩擦焊(friction stir welding, FSW)对接头组织的影响.结合极化曲线测试，比较了紫外光照射与暗态对预沉积NaCl的基材及焊接接头腐蚀行为影响的差异.结果表明，MIG焊接头组织均匀性较差，焊缝Mg含量远高于母材，使得表现出较差的热力学稳定性.紫外光照射加速了铝合金焊接接头的腐蚀，尤其是明显加速了MIG焊接头的腐蚀.30天的紫外光照射对FSW接头的影响与母材相近.这些影响与材料本身的耐腐蚀性能及铝合金表面形成的半导体性质腐蚀产物密切有关.     

闪光焊FeCrAl合金管材的接头组织及性能

采用闪光焊对FeCrAl合金进行对接接头焊接,通过扫描电子显微镜及能谱仪等手段研究了焊接接头的显微组织特征、不同区域氧化物颗粒的分布情况及力学性能. 结果表明,闪光焊焊接FeCrAl合金所得焊接接头显微组织主要为等轴晶,在焊缝和热影响区氧化物未出现明显聚集及向晶界偏聚的现象,且在晶内和晶界都可以呈现弥散分布的特征;焊接接头抗拉强度值达到594 MPa,为母材强度的90.5%;接头断裂在焊缝区,整体呈现脆性断裂模式;焊缝晶粒的粗化导致焊缝区硬度降低,最终引起焊接接头出现软化.     

Microstructure and Properties of TIG/FSW Welded Joints of a New Al-Zn-Mg-Sc-Zr Alloy

A new Al-Zn-Mg-Sc-Zr alloy with low Sc content was welded by tungsten inert gas (TIG) and friction stir welding (FSW) techniques. The microstructure and properties of those two welded joints were investigated by property tests and microstructural observations. The results show that the new Al-Zn-Mg-Sc-Zr alloy has desirable welding property. The ultimate tensile strength and welding coefficient of the TIG joint reach 405 MPa and 76.7%, respectively, and in FSW joint those property values reach 490 MPa and 92.6%, respectively. The studied base metal has a deformed fibrous subgrains structure, many nano-scaled Al₃(Sc,Zr) particles, and very fine aging precipitates. In the TIG joint, the fusion zone consists of coarsened dendritic grains and the heat-affected zone (HAZ) has fibrous micro-scaled subgrains. The FSW welded joint is characterized by a weld nugget zone, thermo-mechanically affected zone (TMAZ), and HAZ. Due to plastic deformation around the rotating pin and anti-recrystallized effectiveness of Al₃(Sc,Zr) particles, the weld nugget zone has a very fine subgrain structure. The TMAZ experiences some dissolution of aging precipitates. Coarsening of aging precipitates was observed in the HAZ. The better mechanical properties of the FSW joint are derived from a fine subgrain structure and homogeneous chemical compositions.     

不同成形状态2195铝锂合金GTAW焊接头的组织与性能

采用喷射沉积2195铝锂合金旋态和锻态材料进行了GTAW对接焊,检测了接头抗拉强度和维氏硬度,观察了接头金相组织及断口形貌,对接头各区域进行了EBSD表征和微观特征量的统计分析,讨论了接头微观组织与力学性能的相关性. 结果表明,旋、锻态材料具有良好的GTAW工艺性,接头抗拉强度达到了各自母材的71%和68%,断后伸长率达到7.3%,拉伸断口呈现出韧性断裂特征. 接头焊缝区金属的小角度晶界比例较低,靠近旋侧的小角度晶界比例为6.4%,靠近锻侧的小角度晶界比例为7.8%;旋侧与锻侧的焊接热影响区及熔合区均趋于一种相似的微结构,母材、热影响区、熔合区及焊缝金属的平均晶粒尺寸依次处于10,10 ~ 15,15 ~ 23,20 ~ 25 μm的水平,具有较好的组织“连续性”,母材晶粒细小、成分均匀的特点在焊接过程中得到了保持,一定程度上展现了喷射沉积铝锂合金材料的应用优势.     

Q550高强钢焊接接头强韧性匹配

在不预热条件下采用不同合金成分焊丝焊接Q550高强钢,试验研究焊丝中合金对焊缝组织、接头抗拉强度及冲击韧性的影响.结果表明,使用MK.G60-1焊丝可获得以针状铁素体为主的焊缝组织.焊缝中沿晶界分布的先共析铁素体在承受拉应力时易萌生裂纹,提高焊缝中针状铁素体含量可以提高接头抗拉强度和韧性.采用MK.G60-1焊丝接头抗拉强度接近母材的抗拉强度,断裂发生在熔合区.接头热影响区的冲击吸收功最高,而熔合区的抗拉强度和韧性最低.焊缝冲击断口纤维区均以穿晶断裂为主,断口韧窝产生的机理是微孔聚集型,针状铁素体区对应的韧窝较大,先共析铁素体对应的韧窝较小.     

搅拌摩擦焊工艺参数对铸态A356铝合金抗拉强度的影响(英文)

A356是一种高强度铝硅铸造态合金,广泛用于食品、化工、船舶、电器和汽车行业。熔焊这种铸造合金时存在许多问题,如孔隙、微裂隙、热裂等。然而,用搅拌摩擦焊(FSW)来焊接这种铸造态合金可以避免上述缺陷发生。研究了搅拌摩擦焊工艺参数对铸造态A356铝合金抗拉强度的影响;对旋转速度、焊接速度和轴向力等工艺参数进行优化;从宏观和微观组织分析角度对焊接区的质量进行分析;对焊接接头的抗拉强度进行了测定,并对抗拉强度与焊缝区硬度和显微组织的相关性进行了研究。在旋转速度1000r/min、焊接速度75mm/min和轴向力5kN的条件下得到的焊接接头具有最高的抗拉强度。     

1561铝合金TIG深熔焊接头组织与力学性能

采用TIG深熔焊工艺,对1561高镁铝合金进行了焊接,并对接头的显微组织和力学性能进行系统分析.结果表明焊缝中无气孔和裂纹缺陷;打底焊道中部存在“∧”字形粗晶区,其上下部晶粒尺寸细小;双层焊经历第二道的盖面焊后,打底焊道晶粒明显长大,熔合区晶粒晶界发生重熔,焊缝软化现象仍有发生;焊缝和热影响区的显微硬度低于母材,但热影响区并没有表现出明显的软化现象.接头抗拉强度可达314 MPa,表明深熔焊工艺适合于1561高镁铝合金的焊接.     

无钴马氏体时效钢电子束焊接接头组织与性能分析

对18Ni无Co马氏体时效钢进行了真空电子束焊接,用金相显微镜观察了焊接接头的组织形貌,并测定了焊缝区、热影响区、基体的显微硬度.结果表明,18Ni无Co马氏体时效钢组织为板条马氏体组织,材料焊接性能良好,焊缝区凝固组织为胞状树枝晶,熔合线附近热影响区晶粒发生了再结晶,晶粒长大明显.硬度分布有明显的规律性,焊缝区硬度最低,细晶区硬度最高,熔合线附近的热影响区,离熔合线越远,硬度值越高.在距熔合线2.5 mm处有一个马氏体与奥氏体两相混合的狭窄区域,硬度较其两侧有明显降低.     

新型Al-Zn-Mg-Cu合金TIG焊接头组织与性能研究

本文对一种Al-Zn-Mg-Cu-Mn-Zr-Er合金薄板进行了全自动TIG填丝焊接,观察接头微观组织形貌,并测试其力学性能。结果显示焊缝未出现典型的联生结晶形貌,而是由等轴细晶粒层和大量等轴树枝晶构成,在晶界或枝晶间断续分布复合T（AlZnMgCu）相;焊接热影响区因沉淀相变化,硬度值不同,分为近缝的固溶区和远缝的过时效区,晶粒保持与母材相同的拉长形貌,未见明显长大;接头横截面的显微硬度最低值在焊缝,约为120HV,母材显微硬度约为184HV,接头抗拉强度为421.75MPa,达到母材的65.08%,拉伸断裂位置处于焊缝中,断口形貌为典型的韧性断裂,等轴韧窝底部存在破碎的第二相颗粒,其成分与焊缝中复合T相基本一致。     

镀锌薄板TIG拼焊的焊缝组织及成形性能

采用钨极惰性气体焊对镀锌薄板 SGCC 实施等厚拼焊,测试分析了拼焊板焊接接头的金相组织、显微硬度,并对拼焊板和母材试样进行杯突试验.结果表明,在拼焊过程中,母材的散热情况不同会造成焊缝金相组织在靠近母材的局部区域有很大差异.焊缝熔合区组织为粗的片状与块状先共析铁素体沿柱状晶界分布,晶内为魏氏体组织和片状珠光体,热影响区为块状的珠光体和铁素体,导致了焊缝及其热影响区的硬度均高于母材,对拼焊板的整体成形性能产生负面影响;同时,焊缝杯突值较母材有一定程度的降低,揭示其焊缝深冲性能低于母材.

Abstract：

The microstructure and micro-hardness of welded joint of SGCC by tungsten inert-gas (TIG) welding are studied, and the cupping test of Tailor-welded blank and base metal are studied.The results show that in the welding process, the microstructure of weld will have great diversity at local region closing parent metal because of the different cooling condition of the parent metal. The microstructure of welding fusion zone is massive sheet proeutectoid ferrite distribution along the columnar grain boundaries, intragranular organizations are Widmanstatten and sheet pearlite structure, and the microstructure in HAZ is massive pearlite and ferrite, which make the micro-hardness value of welding seam and HAZ higher than that of base metal and lead negative influence to the formability of Tailorwelded blank. The cupping value of weld seam reduces to some extent compared with that of base metal, which indicates that the formability of weld seam is not good as that of base metal.     

Al-Mg-Mn-Sc-Zr合金板材搅拌摩擦焊和氩弧焊焊接接头的对比

研究Al-Mg-Mn-Sc-Zr合金的焊接工艺和焊接接头组织和性能。采用搅拌摩擦焊（FSW）和氩弧焊（TIG）2种焊接工艺对该合金的热轧和冷轧-退火2种使用态板材进行焊接。采用比较研究的方法测定和研究焊接接头的力学性能和显微组织,利用光学显微镜和透射电子显微镜研究焊缝的显微组织和力学性能之间的关系。结果表明,与基材相比,Al-Mg-Mn-Sc-Zr合金的热轧和冷轧-退火板材的FSW和TIG焊接接头的强度均下降,但FSW焊接系数高于TIG焊接系数。这是因为FSW焊接接头焊核区亚结构强化的丧失和Al3（Sc,Zr）的析出强化作用的极少量丧失,而TIG焊焊接接头的软化主要原因是其形变强化的完全丧失和Al3（Sc,Zr）的析出强化作用的大部分丧失,且搅拌摩擦焊焊核区晶粒比TIG焊的焊缝区晶粒更细小。     

2219-T651铝合金激光摆动焊接接头微观组织和力学性能

采用激光摆动焊接技术对2219-T651铝合金进行了不同摆动幅度和频率下的焊接试验,研究了摆动工艺参数、焊缝气孔率和宏观成形、接头组织和性能之间的内在联系.结果表明,与无摆动焊接相比,激光摆动焊接可以降低焊缝气孔率,尤其随着摆动幅度的增加,当摆动幅度为2.5 mm时,气孔率降至1.66%.与母材相比,热影响区和熔化区发生软化.靠近焊缝的热影响区,由于沉淀强化作用的变弱,硬度逐渐降低,直至出现“平台”.而由α(Al)基体以及枝晶间和晶界α(Al)+θ(Al₂Cu)共晶相组成的熔化区,因铜的偏析导致固溶强化效果被削弱,表现出最低的硬度.此外,部分摆动参数下焊缝晶粒尺寸有所细化,这引起了其硬度的略微升高.当摆动频率为150 Hz和摆动幅度为2.5 mm时,接头的抗拉强度高达318 MPa,约为母材抗拉强度的69.4%,接头抗拉强度与断口孔洞面积占比呈线性负相关关系,焊缝气孔率是影响焊态接头抗拉强度的主要因素.     

Grain growth behaviour and high strain rate tensile properties of gas tungsten arc welds in iridium alloy DOP–26

Abstract

The high strain rate tensile ductilities of gas tungsten arc welds in an Ir–0.3 wt-%W alloy containing 60 wt-ppm Th (designated DOP–26) have been determined at test temperatures of 900–1200°C. Within this temperature range, the welded specimens of DOP–26 exhibited tensile ductilities of 9–15%, independent of the test temperature. These values are comparable to those of unwelded DOP–26 tensile specimens tested at temperatures below 1000°C, but significantly lower than (approximately half) those of unwelded DOP–26 tested above 1000°C. Elongation measurements at points along the gauge length of tensile tested specimens indicated that ductility was fairly uniform across the base metal and weld regions. At a tensile test temperature of 900°C, fracture occurred in the base metal with a mixed intergranular–transgranular failure mode. At 980°C and above, fracture occurred along the grain boundaries in the centreline of the weld. Scanning electron microscopy of fracture surfaces revealed the presence of numerous secondary phase particles along grain boundaries in the weld region. These particles were rich in thorium and were identified as an Ir–Th eutectic phase (melting point ～2080°C) that formed as the weld pool cooled. These particles, and the larger grain size of the fusion zone compared with the base metal, contributed to the lower tensile ductilities of the welded specimens compared with unwelded specimens. Because high strain rate tensile ductility in this alloy is strongly dependent on grain size, the grain growth behaviour of welded specimens of the alloy was also studied. In as welded specimens, the average grain diameters (measured through the thickness of the specimens in a plane perpendicular to the welding direction) in the base metal, weld centreline, and fusion zone were ～21, 41, and 72 µm respectively. For annealing times up to 1065 h at 1400°C and up to 100 h at 1500°C, grain sizes in the weld centreline and in the fusion zone did not change significantly. For these same anneals the base metal grain size increased gradually to 45 and 58 µm for 1400 and 1500°C annealing respectively. The base metal grain sizes were comparable to previous data from unwelded specimens of this alloy. However, excessive grain growth for an annealing time of 250 h at 1500°C was observed and as yet is unexplained.     

6061铝合金FSW接头与MIG焊接头对比试验

采用搅拌摩擦焊(FSW)和MIG焊分别对6061铝合金板进行了焊接试验,测试了焊接接头的强度,观察了焊接接头的金相组织,并进行了接头的硬度分布测试.结果表明,搅拌摩擦焊接头抗拉强度高达212.05 MPa,是母材抗拉强度的86％,比MIG焊的接头强度略高.焊接接头软化区宽度比MIG焊接头软化宽度窄.6061铝合金母材为典型的轧制组织,焊核区为细小的等轴晶组织,MIG焊接头焊缝为柱状晶组织.     

TC4厚壁管全位置PAW工艺及接头性能分析

介绍了一种适合TC4钛合金厚壁管的等离子弧焊接新工艺,通过对工艺参数分区控制和优化匹配,实现了钛合金管道全位置优质焊接.采用光学显微镜、扫描电镜以及显微维氏硬度仪分别对特征位置焊接接头的显微组织、断口形貌以及显微硬度进行表征.结果表明,特征位置接头焊缝区及热影响区显微组织均主要由网篮状α'相、针状α相以及粗大β相组成;接头拉伸性能良好,拉伸试样均断裂于母材处;冲击试样的断裂形式为韧性断裂;焊缝区及热影响区硬化区的硬度值高于母材.     

镁合金MIG焊接工艺及焊接接头组织性能分析

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.

Abstract：

The pulsed MIG welding was used to weld AZ31B Mg alloy, and the weldability of the alloy was studied. The microstructure, mechanical property and hardness of the welded joint were investigated via the metal phase microscopy, scanning electron microscope, tensile testing machine and hardness instrument. The results show that one-side 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 surface defects.The heat-affected zone of the joints is narrow, and the grains of the zone are slightly larger than that of the base metal. The grains of fusion zone are tiny, the microstructure is homogeneous and the hardness of welded joint is higher than that of the base metal. The tensile strength is up to 95% of the base metal.     

Microstructures and mechanical properties of a welded CoCrFeMnNi high-entropy alloy

The response of the CoCrFeMnNi high-entropy alloy to weld thermal cycles was investigated to determine its applicability as an engineering structural material. Two processes were used: high-energy-density, low-heat-input electron beam (EB) welding and low-energy-density, high-heat-input gas tungsten arc (GTA) welding. Weldability was determined through comprehensive microstructural and mechanical property characterisation of the welds. The welds did not develop solidification cracking or heat-affected zone cracks. The microstructures in weld fusion zones are similar to that in the as-cast materials, consisting of large columnar grains with dendrite. The dendrite arm spacing and the extent of elemental segregation were less in the welds than in the cast ingot, and also were less pronounced in the EB weld than in the GTA weld. Compositional microsegregation between dendritic cores and interdendritic regions of the welds was insignificant. Both welds exhibited slightly higher yield strengths than the base metal. The EB weld possessed comparable tensile strength and ductility to that of the base metal. In comparison, the GTA weld maintained ～80% of the base metal’s tensile strength and 50% of the ductility.     

“原位观察”下的水龙头激光焊接头腐蚀性能分析

采用低耗能激光焊新工艺制造水龙头薄壳,替代传统高污染、高耗能的整体铸造工艺,对304、310 s不锈钢激光焊接头进行沸腾硫酸-硫酸铁及室温浸蚀对比腐蚀研究.在设定的腐蚀时间内,采用“原位观察”腐蚀过程焊缝及熔合区微观组织变化.结果表明,310 s比304耐腐蚀性更好,随腐蚀时间加长,接头熔合区晶粒晶界未明显加宽,焊缝断口微观特征主要为韧窝,证明其未发生晶间腐蚀.焊缝金属成分分析表明焊缝中心晶粒与母材相近,腐蚀沟Cr元素降至20.81%高于12%,保证其耐腐蚀性能.