Friction stir welding of twin-roll cast EN AW 3003 plates

Twin-roll cast EN AW 3003 plates were butt-welded with friction stir welding and their structural features were identified. Sound welds were obtained in twin-roll cast EN AW 3003 plates at tool rotation speeds higher than 500 rpm. The ultimate tensile strength of the welded plates was 134 ± 3 MPa, comparable to the ultimate tensile strength of the original plate, at 146 MPa. The stirring action of the pin fractured the interdendritic network and coarse eutectic cells, replacing the dendritic features of the base plate with a uniform dispersion of very fine intermetallic particles across the stir zone. The thermal and mechanical cycles introduced during FSW relaxed the supersaturation of the cast plate, leading to the precipitation of intermetallic particles. This precipitation activity produced a particle population gradient that peaks inside the stir zone and dictates the etching response across the plate section. The material in direct contact with the rotating pin is severely deformed and is exposed to frictional heating and inevitably undergoes dynamic recrystallization. The very fine grain structure thus obtained suffers abnormal grain growth when annealed at high temperatures due to the effective pinning of the grain boundaries by the fine particles.     

焊后热处理对6063铝合金激光填丝焊接头组织与性能的影响

采用激光填丝焊对6063铝合金进行焊接,并对焊接接头进行人工时效和固溶+人工时效的热处理。通过光学显微镜、扫描电镜观察及拉伸试验,对焊后经不同热处理的焊接接头组织和性能进行研究。结果表明:未热处理的焊接接头抗拉强度为196 MPa,焊缝内部为铸态组织,弥散分布着Mg₂Si强化相,熔合线附近存在向焊缝内部生长的粗大柱状晶,焊缝内部为细小的树枝晶,焊缝中心为等轴晶;经时效处理后,焊接接头组织不均匀性和强化相的分布得到改善,焊接接头抗拉强度提高27 MPa;经固溶+时效处理的焊接接头抗拉强度提高64 MPa,焊缝组织、熔合区及热影响区组织得到显著细化。焊接接头均为韧脆混合断裂;时效处理的断口韧窝大小差异较大,韧窝较深;固溶+时效处理后的断口韧窝大小均匀,韧窝尺寸较大较深,韧窝数量更多。     

热输入对BWELDY960Q钢焊接接头组织性能的影响

采用MAG焊方法焊接低合金高强度钢BWELDY960Q,在不同焊接工艺参数下获得焊接接头,研究焊接热输入对焊接接头组织性能的影响. 结果表明,随着焊接热输入的提高,焊缝中针状铁素体的体积分数呈现先增加后减少的趋势,当焊接热输入为12.32 kJ/cm时,焊缝中获得的针状铁素体所占的比例达到最大值. 针状铁素体数量的增加,提高了焊缝和熔合区的冲击吸收功、焊接接头的抗拉强度、断后伸长率和断面收缩率. 焊缝冲击断口呈韧窝花样,等轴韧窝与抛物线韧窝交替分布. 熔合区冲击断口呈解理特征,解理台阶层次明显,并存在较多的撕裂棱.     

Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas (VPTIG) welding process and the effects of post weld heat treatment (PWHT) on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded (AW) sample and PWHT sample. The PWHT method used on the samples was solution treatment (535 °C, 30 min), water quenching and artificial aging (175 °C, 12 h). The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively.     

6082-T6铝合金搅拌摩擦焊组织演变与力学性能

通过透射电子显微镜、扫描电子显微镜、拉伸试验机和显微硬度计对6082-T6铝合金搅拌摩擦焊接头焊缝区组织演变和力学性能进行分层研究. 结果表明,在焊核区上层,材料发生塑性变形,晶格畸变能增加,为降低能量,大量的位错集聚成亚结构边界发生动态回复. 同时在焊接热循环的作用下发生动态再结晶,导致焊缝区上层晶粒细小. 在焊核区下层,主要受到搅拌针搅拌作用,轴肩产热通过扩散过程传递到下层的热量减少,发生动态回复和动态再结晶程度低于焊缝上层,晶粒粗大. 前进侧和后退侧热影响区均出现棒状β′沉淀相. 对应焊缝上、下两层硬度都呈“W”形分布,焊缝上层硬度高于焊缝下层硬度,最小值出现在前进侧. 沿着焊缝长度方向上层和下层的抗拉强度分别为205,186 MPa,呈降低趋势,为韧性断裂.     

TiAl金属间化合物电子束焊接头应力场分布特征

采用热弹塑性有限元方法,对TiAl金属间化合物平板电子束焊接接头的焊接应力进行了三维数值模拟,并分析了应力分布状态与裂纹特征之间的关系.结果表明,沿焊缝方向σx为残余拉应力,在焊道中部维持在较高水平,最高拉应力为390MPa.焊道中部横截面σx方向为残余拉应力,在热影响区附近达到最大值415 MPa,σy方向也为残余拉应力,且在距焊缝中心1.9 mm处达到最高值160 MPa左右.在不同焊接热输入条件下接头最高抗拉强度为304.7 MPa,断裂发生在接头热影响区附近,即残余应力最大的区域.     

Microstructure and mechanical properties of nanostructured bainite weld with regeneration

Because of the brittle martensite crystalline structure, nanostructured bainitic steel is very difficult to be welded and easily form cracks in the welded joint, which limits the scope of their application. Regeneration treatment can lead to nanostructured bainite formation in the welded joints, preventing further degradation of the welded joint. Detailed changes of microstructures and mechanical properties of the weld are characterized here. Coarse inter-dendrite structures appear in the weld due to welding segregation, and are confirmed to be retained austenite by TEM. Moreover, an extraordinary combination of strength and ductility of the weld is achieved. The ultimate tensile strengths are 1913MPa and 2115MPa when regeneration temperatures are 250 °C and 230 °C. The corresponding elongations are 5.14% and 2.3%. In addition, the tension fracture behaviour and crack propagation mode of the weld are investigated.     

铝合金T形接头静止轴肩搅拌摩擦焊接及组织性能分析

成功实现了2219C10S铝合金T形接头的静止轴肩搅拌摩擦焊接,焊缝表面光滑平整,无明显减薄.从基板背部进行的超声相控阵检测结果表明,基板与肋板对合面全部焊透,接头内部无超标缺陷.接头横截面宏观金相可以观察到2个以肋板中心线对称分布的焊缝轮廓,单侧焊缝轮廓均超过了肋板中心线.接头横截面显微硬度分布趋势呈独特的“U”形,焊核区显微硬度最低.T形接头两个方向的拉伸试样起裂点位于“拉伸方向板材与接头R₁圆角的相切处”,但拉断试样断裂面的横穿区域存在较大差异,这也是沿肋板方向的抗拉强度比沿基板方向低20 MPa的主要原因.     

Microstructure and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints

The microstructure evolution and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints under different welding parameters were studied. The results show that the weld fusion zone of TC4/TA15 dissimilar welded joints consists of coarsened β columnar crystals that contain mainly acicular α′ martensite. The heat affected zone is composed of the initial α phase and the transformed β structure, and the width of heat affected zone on the TA15 side is narrower than that on the TC4 side. With increasing temperature, the yield strength and ultimate tensile strength of the TC4/TA15 dissimilar welded joints decrease and the highest plastic deformation is obtained at 800 °C. The tensile strength of the dissimilar joints with different welding parameters and base material satisfies the following relation (from high to low): TA15 base material > dissimilar joints > TC4 base material. The microhardness of a cross-section of the TC4/TA15 dissimilar joints reaches a maximum at the centre of the weld and is reduced globally after heat treatment, but the microhardness distribution is not changed. An elevated temperature tensile fracture of the dissimilar joints is located on the side of the TC4 base material. Necking occurs during the tensile tests and the fracture characteristics are typical when ductility is present in the material.     

G115钢CMT + P焊接工艺及组织和性能

基于冷金属过渡加脉冲(CMT + P)的焊接方法,研究了新型回火马氏体耐热钢G115的焊接性以及焊接接头组织和性能. 结果表明,焊接接头经热处理后为回火马氏体组织,焊缝晶粒呈现出等轴晶和柱状晶两种不同的形貌,而焊接热影响区和母材晶粒均为等轴晶. 与焊条电弧焊(SMAW)相比,CMT + P焊接方法有效降低了热输入,大幅度减小了热影响区宽度,提高了焊接接头的拉伸性能和热影响区冲击韧性,焊接接头焊缝冲击韧性略有降低. 焊接接头的室温和高温拉伸断裂机理均为韧性断裂,室温拉伸断口的韧窝内存在一定量的析出相.     

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.     

Effect of cathodic protection on ductility of X65 linepipe steel weldments

Abstract

The combined effects of strain rate, monotonic loading, and cathodic protection and overprotection on the mechanical properties of X65 linepipe steel parent plate and gas metal arc weld metal have been investigated in NaCl solution. The results obtained on longitudinal all parent plate and all weld metal specimens indicate that the latter material, having a higher hardness and strength level, is more susceptible to environmental cracking due to cathodically evolved hydrogen entering the steel. However, with transverse specimens, taken perpendicular to the weld, the gauge length contains parent plate, heat affected zone material, and weld metal. In this case, irrespective of the greater inherent susceptibility of the weld metal, environmental cracking and failure always occur in the parent plate. This result is attributed to the ultimate tensile strength of the lower strength parent plate being exceeded at stress levels significantly lower than the yield strength of the higher strength weld metal. The practical implications of these results are discussed. In addition, the results are presented of a fractographic analysis which relates the morphology of the environmentally induced fracture surfaces to microstructural features in the weld metal and the parent plate.     

Static tensile strength characteristics of fillet welding lap joints assisted with bonding

A series of tensile tests were carried out on fillet welded lap joints assisted with bonding for investigating the static tensile strength characteristics of the joints from the viewpoints of stress reduction effect around the welded part due to bonding. It was confirmed that the mechanical properties of epoxy resin bonding used in this study were not deteriorated by heating to less than 150°C. When the fillet welded lap joints with bonding were assembled, the bond layer 20 mm from the weld toe was subjected to heating to over 150°C. In other words, the mechanical properties in that region deteriorated. The strengths of the elastic limits of specimens with welding and bonding were higher than those of specimens with only welding by from 60 to 100 MPa. The ultimate tensile strengths of them were almost the same because they were broken at the base plate. The strains around the weld toe and the root of specimens with welding and bonding were smaller than those of specimens with welding by around 13% in the elastic region. The strengths of specimens with only bonding were 170 MPa, which could be explained by a theory of elastic stress distribution. Even if the bond layer 20 mm from weld toe of the specimens with welding and bonding was thermally damaged, the possibility was confirmed that the residual bond layer had around 100 MPa in strength. It could be concluded that the strength of the residual bonding assisted to decrease the stress around the welded part of the specimens with welding and bonding.     

环焊接头强度对高应变海洋管道轴向承载能力的影响

基于应变设计的油气输送管道,环焊接头的强度对管道轴向变形能力起着至关重要的作用。以OD559×31.8 mm L485高应变海洋管道环缝为研究对象,采用有限元方法和数字图像相关法(DIC)拉伸试验及宽板拉伸试验,研究了GMAW环焊接头不同区域的强度变化对管道轴向承载能力的影响。结果表明,随焊缝金属强度的升高,管道轴向极限载荷和轴向平均应变增大,失效位置由焊缝向热影响区和母材转移;根焊金属占比小,热影响区很窄,高强匹配时根焊金属和热影响区强度对管道轴向极限载荷和轴向平均应变影响较小;在轴向载荷下,低强匹配环焊接头的母材、热影响区和焊缝的轴向应力和轴向应变分布极不均匀。受母材的拘束作用和焊缝金属自身的形变强化,低强匹配焊接接头的抗拉强度高于全焊缝金属,但变形和屈服主要集中在焊缝区域,容易导致管道环焊缝断裂失效。     

Microstructure evolution and tensile properties of friction-stir-welded AM50 magnesium alloy

Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties were investigated by using hardness measurement and tensile test,and the fractographs were observed by scanning electron microscopy.The results show that the microstructure of the base material was characterized by bulk primaryαphase,α-matrix and intermetallic compoundβ(or Mg_(17)Al_(12)),and t...     

Friction stir welding of aluminium lap joint by tool without probe

A friction stir welding process, with a rotating tool without a probe, was employed and applied to a lap joint of aluminium plate. The thickness of the aluminium plates was 0.5 mm. New tool shapes were developed. The tops of the tool were dome shaped. In this process, the rotating tool was plunged into the aluminium plate. The tool-rotating axis was vertical to the specimen surface, and then moved in the welding direction at a speed of 20 mm/s. Tool rotation speed was 18,000 rpm.

At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. At tool plunge depth of 0.1 mm, its joint was fractured at the weld interface. At tool plunge depth of 0.2 mm or over, the joints were fractured at the stir zone of the upper plate or the heat affected zone of the lower plate. Based on observation of the hardness profiles and the thickness change of the weld area, controlling factors of the joint strength are discussed.     

搅拌针形状对6082-T6铝合金静轴肩搅拌摩擦焊接头组织与性能的影响

采用四种形状的搅拌针对3mm厚的6082-T6铝合金进行静轴肩搅拌摩擦焊焊接，研究了不同形状搅拌针焊接接头的宏观形貌，微观组织，力学性能和断口形貌，以及搅拌针的产热。结果表明三角形搅拌针与四边形搅拌针产热较低，动静体积比较大，接头处塑性金属流动性强，焊接过程中焊缝顶部与底部温差较小，可以形成无缺陷的SSFSW接头；XRD分析表明，焊核区无新的物相产生，三角形搅拌针焊接接头焊核区微晶尺寸最小；各接头的硬度均呈“U”形分布，最低点位于后退侧热机影响区与焊核区交界处，三角形搅拌针接头的硬度整体略高；三角形搅拌针焊接接头的抗拉强度与断后伸长率最高，分别为202.9MPa和3.8%；拉伸断口形貌分析表明，所有接头均为韧性断裂。     

5A02铝合金C O2激光焊接头组织和力学性能分析

对2mm厚的5A02铝合金进行C02激光焊接试验研究.分析激光焊缝成形和接头微观组织形态,测定了接头上表面和焊缝厚度方向上的维氏硬度,并对接头进行横向和纵向拉伸试验,用扫描电镜观察分析拉伸断口形貌.结果表明,激光功率和焊接速度合理匹配能够获得成形良好、无缺陷的焊缝,焊缝中部为等轴细晶,熔合线附近是柱状晶组织.焊缝各区域...     

Weldability evaluation of high tensile plates using GMAW process

High tensile plates, SAILMA-450 high impact (HI) (yield strength, 45 kg/mm² minimum; ultimate tensile strength, 57 kg/mm² minimum; elongation, 19% minimum; Charpy impact energy 2.0 kg.m at −20 °C minimum) were successfully developed at the Steel Authority of India Ltd., up to 32 mm plate thickness. Since then the steel has been extensively used for the fabrication of impellers, bridges, excavators, and mining machineries, where welding is an important processing step. The present study deals with the weldability properties of SAILMA-450 HI plates employing the gas metal arc welding process and carbon dioxide gas. Implant and elastic restraint cracking tests were conducted to assess the cold cracking resistance of the weld joint under different welding conditions. The static fatigue limit values were found to be in excess of minimum specified yield strength at higher heat input levels (9.4 and 13.0 kJ/cm), indicating adequate cold cracking resistance. The critical restraint intensities, K _cr, were found to vary between 720 and 1280 kg/mm², indicating that the process can be utilized for fabrication of structures involving moderate to low restraint intensities (200 to 1000 kg/mm²). Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 10 to 27 kJ/cm showed no incidence of lamellar tear upon visual, ultrasonic, and four-section macroexamination. These tests were repeated using machined plates, such that the midthickness of the plates (segregated zone) corresponded to the heat affected zone of the weld. No cracks were observed, indicating good lamellar tear resistance of the weld joint. Optimized welding conditions were formulated based on these tests. The weld joint was subjected to extensive tests to assess the physical properties and soundness of the weld joint. The weld joint exhibited good strength (64.7 kg/mm²) and impact toughness (5.7 and 3.5 kg.m at −20 °C for weld metal and heat affected zone properties. Crack tip opening displacement (CTOD) tests carried out for parent metal, heat-affected zone, and weld metal resulted in δm values of 0.41, 0.40, and 0.34 mm, respectively, which indicates adequate resistance to cleavage fracture. It was concluded that the weld joint conforms to the requirements of SAILMA-450 HI specification and ensures a high integrity of the fabricated products.     

TC17钛合金线性摩擦焊接头组织及力学性能分析

针对固溶时效态TC17钛合金焊态及焊后热处理态线性摩擦焊接头,进行显微组织及力学性能对比分析. 结果表明,焊态时焊缝组织发生了回复与再结晶,由于焊后冷却速度较快,生成了亚稳定β相,焊缝区发生了软化;热力影响区组织沿受力变形方向拉长、细化、交替呈带状分布,加工硬化程度较高,显微硬度明显高于其它区域;热影响区由于二次次生α相基本溶解于亚稳定β相,导致显微硬度显著降低. 经过焊后热处理,亚稳定β相发生时效分解,析出了弥散程度更高的针状次生α相使得焊接区硬度大幅度提高. 由于亚稳定相的生成,焊态接头发生软化,拉伸均断裂在焊缝区,抗拉强度达到母材强度91.8%,断口呈脆性断裂形态;焊后热处理态接头由于二次次生α相的析出,起到弥散强化的作用,拉伸试验均断在母材,断口呈典型韧性断裂形态.