A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比

研究了6N01-T5铝合金搅拌摩擦焊(FSW)和氩弧焊(MIG)接头不同部位的疲劳裂纹扩展性能, 并对疲劳断口和接头组织进行了分析. 结果表明,对于FSW和MIG焊接头, 其裂纹扩展速率从高到低的部位依次为焊缝(核)区、热影响区和母材. 裂纹在FSW和MIG焊接头相同区域的扩展速率无明显差别, 然而裂纹在FSW接头细晶组织中开始扩展所需的门槛值ΔK要比对应的MIG焊接头高, 总体上其裂纹在FSW焊核区的抗疲劳裂纹扩展性能要优于对应的MIG焊缝区. 裂纹在FSW和MIG焊接头焊核(缝)区扩展的疲劳断口表现为脆性断裂, 而在热影响区则以规则和光滑的疲劳条纹形式扩展.     

搅拌摩擦焊和熔化极气体保护焊6082铝合金疲劳性能分析

对10 mm厚6082-T6铝合金进行搅拌摩擦焊(FSW)和熔化极气体保护焊(MIG焊)焊接,利用疲劳性能试验机、光学显微镜、扫描电子显微镜等手段对6082铝合金FSW和MIG焊接头的疲劳力学性能、微观组织、裂纹扩展特征、疲劳断口进行了分析. 结果表明,在疲劳寿命为2×106周次时,6082铝合金母材及其FSW和MIG焊接头的名义应力分别为126.3,110.2,84.2 MPa;在高应力水平下(Δσ=160 MPa),FSW接头疲劳寿命明显大于MIG焊接头、与母材的疲劳寿命相当. MIG焊疲劳断口均位于焊趾处,焊缝内的气孔缺陷为其主要裂纹源;FSW疲劳断口大多发生在轴肩边缘. 接头的微观断口具有准解理特征,断口中存在疲劳条纹和韧窝.     

铝合金搅拌摩擦与MIG焊接接头疲劳性能对比试验

根据疲劳S-N曲线试验结果,对5A06铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳性能进行了初步比较,分析讨论了搅拌摩擦焊过程中所产生的焊接缺陷对其疲劳性能的影响.结果表明,在焊态下由于焊接接头几何形状等的影响,FSW的疲劳强度明显高于MIG焊接接头;对FSW焊缝根部的"吻接"缺陷(kissing-bonds)是降低FSW焊接接头疲劳寿命的主要因素,旋转搅拌工具在焊缝表面形成的多余飞边将对疲劳行为产生明显影响.     

搅拌摩擦焊AA7075-T651铝合金接头的疲劳裂纹扩展(英文)

研究12 mm厚AA7075-T651铝合金板搅拌摩擦焊接头的疲劳裂纹扩展行为。从搅拌摩擦焊接头以及母材中截取试样,对试样进行疲劳裂纹扩展实验。对搅拌摩擦焊接头以及母材的横向拉伸性能进行评估。用光学显微镜和透射电镜分析焊接接头的显微组织。用扫描电镜观察试样的断裂表面。与母材相比,焊接接头的ΔKcr降低了10×10-3 MPa·m1/2。搅拌摩擦焊AA7075-T651接头的疲劳寿命明显低于母材的,其原因可归结于焊缝区的析出相在搅拌摩擦焊接过程中的溶解。     

厚板铝合金FSW和MIG焊接接头疲劳性能

对厚度10 mm的6082-T6铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳强度进行了试验研究,并与6082-T6母材疲劳性能进行了对比分析.结果表明,6082-T6母材的疲劳S-N曲线最高、MIG焊接接头S-N曲线度最低,而FSW接头的疲劳S-N曲线近似位于两者之间;在高应力区FSW疲劳强度低于MIG焊接接头、而在低应力区高于MIG焊接接头.大部分FSW试样疲劳裂纹启始于焊缝根部的"弱连接"缺陷,采用机械加工去掉1.4 mm厚度焊缝根部材料后,FSW疲劳强度明显提高并接近母材数据.厚板6082-T6铝合金FSW焊缝根部质量控制是影响疲劳性能的关键因素.     

7050铝合金搅拌摩擦焊接头超高周疲劳性能

采用超高周疲劳试验系统研究7050-T7451铝合金搅拌摩擦焊接头的超高周疲劳性能. 试验结果表明,焊接接头在107周次以上仍然会发生疲劳失效,S-N曲线在108周次左右出现转折点,呈折线型下降;通过SEM对超高周疲劳断口形貌进行观察发现,当应力范围较高时,试件的疲劳裂纹往往在表面萌生,随着应力范围的降低,裂纹有亚表面和内部萌生的倾向;裂纹萌生位置取决于表面起裂和内部起裂相互竞争的结果;试件的断裂位置多为焊接接头的热力影响区和热影响区,EBSD和接头硬度的分析结果表明断裂位置与接头组织不均匀密切相关.     

Fatigue properties of friction stir welded butt joint and base metal of MB8 magnesium alloy

The fatigue properties of friction stir welded(FSW) butt joint and base metal of MB8 magnesium alloy were investigated.The comparative fatigue tests were carried out using EHF-EM200K2-070-1A fatigue testing machine for both FSW butt joint and base metal specimens.The fatigue fractures were observed and analyzed using a scanning electron microscope of JSM-6063 LA type.The experimental results show that the fatigue performance of the FSW butt joint of MB8 magnesium alloy is sharply decreased.The conditional fatigue limit(2 × 10~6) of base metal and welded butt joint is about77.44 MPa and 49.91 MPa,respectively.The conditional fatigue limit(2 × 10~6) of the welded butt joint is 64.45%of that of base metal.The main reasons are that the welding can lead to stress concentration in the flash area,tensile welding residual stress in the welded joint(The residual stress value was 30.5 MPa),as well as the grain size is not uniform in the heat-affected zone.The cleavage steps or quasi-cleavage patterns present on the fatigue fracture surface,the fracture type of the FSW butt joint belongs to a brittle fracture.     

5083铝合金搅拌摩擦焊与MIG焊缝腐蚀性能对比

对5083铝合金FSW（搅拌摩擦焊）和MIG（熔化极氩弧焊）焊缝的微观显微组织和腐蚀性能进行了分析.结果表明,FSW焊缝由细小的等轴再结晶组织构成,而MIG焊缝晶粒粗大,组织不均匀.电化学腐蚀试验表明,主轴旋转频率为300 r/min,焊接速度为160 mm/min,搅拌头倾角为3°的FSW焊缝与MIG焊缝相比,腐蚀电...     

TC4钛合金薄板激光焊接接头的疲劳寿命及断口分析

研究了TC4钛合金薄板激光焊接接头及母材的疲劳性能,并对其疲劳断口进行了观察.结果表明,接头的疲劳寿命在低应力水平时高于母材,在高应力水平时低于母材.母材疲劳裂纹萌生于试样表面;在裂纹扩展区有平行排列的弯曲的二次裂纹和期间更细的疲劳辉纹,瞬断区为细小的等轴韧窝.焊缝疲劳裂纹起源于表面的气孔,源区有笔直且平行排列的二次裂纹;在裂纹扩展区,断口形貌与组织有关,细晶区为韧窝,在细晶与柱状晶交界处为敞口浅韧窝,柱状晶和粗晶区为晶粒大小的刻面,上有大量的微剪切滑移带,断裂机理为滑移带形成及开裂.     

Static shear strength and fatigue life of refill friction stir spot welded AA 6061-T6 sheets

This study was aimed at evaluating the static shear strength and fatigue properties of the newly developed refilled friction stir spot welded AA 6061-T6 joints. The keyhole, the process disadvantage of conventional friction stir spot welding, was refilled successfully, using an additional filler plate, with specially designed tools. Two different tool profiles, namely, convex and concave, were used for the refilling process. Sound and defect free joints were obtained by the refilling process. Joints refilled with convex tools showed better static shear strength than those with the concave ones. The variation of microhardness in different regions of the weld was analysed. Fatigue tests were conducted on the lap shear specimens at a stress ratio of R?=?0·1. The optical micrographs of the welds after fatigue failure in both the conventional and refilled processes were examined to study the fatigue crack propagation and failure modes.     

Comparative study on fatigue properties of friction stir and MIG-pulse welded joints in 5083 Al-Mg alloy

The objective of this investigation was to compare the fatigue properties of friction stir welds with those of MIG-pulse welds. The 5083 Al-Mg alloy was welded by single pass friction stir welding（FSW） and double-sided MIG-pulse welding. The results show that friction stir（FS） welds have a better appearance than MIG-pulse welds for the lack of voids, cracks and distortions. Compared with the parent plate, FSW welds exhibit similar fine grains, while MIG-pulse welds display a different cast microstructure due to the high heat input and the addition of welding wire. The S-N curves of FSW and MIG-pulse joints show that the fatigue life of FS welds is 18 - 26 times longer than that of MIG-pulse welds under the stress ratio of 0.1 and the calculated fatigue characteristic values of each weld increase from 38.67 MPa for MIG-pulse welds to 53.59 MPa for FSW welds.     

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.     

Fatigue behaviour of out-of-plane gusset joints with one-side fillet weld

In previous studies, many fatigue tests have been performed to investigate the fatigue behaviour of out-of-plane gusset welded joints. However, fatigue behaviour of out-of-plane gusset joints with a one-side fillet weld has not yet been clarified sufficiently. In this research, in order to quantitatively clarify the behaviour, welding residual stress at the weld toes of the joint was measured by a cutting method. In addition to this, fatigue tests were carried out on the joints with a one-side weld and turn-around weld. The plate thickness is 9 mm and the weld size is 10 mm. Moreover, finite element stress analyses were conducted on the test specimen models and parametric models with different main plate and gusset plate thickness. Their results show that fatigue cracks for out-of-plane gusset joints with a one-side fillet weld initiate from both weld toes at the start and end points of weld beads and non-penetration weld of the gusset side. Also, the crack initiation points are different depending on the weld arrangement; however, their fatigue strengths are almost same.     

Fatigue crack growth under a constant amplitude loading of Al-6061-T6 welds obtained by modified indirect electric arc technique

Abstract

The characteristics of the fatigue crack growth in the base metal, weld metal and heat affected zone (HAZ) were quantified by testing compact type specimens of 6061-T6 welds obtained by the modified indirect electric arc technique. The fatigue crack growth depends on the microstructure imposed by the welding thermal cycle and it was observed that in the HAZ the crack growth rate is lower than that in the weld metal, but higher than that in the base metal. Microhardness maps revealed that this behaviour is due to the formation of a larger plastic zone around of the crack tip produced by loss of hardening. A comparison of fatigue crack growth of weld metal and HAZ for modified indirect electric arc and friction stir welding shows that the weld metal produced by friction stir welding exhibits better resistance to crack propagation, but both processes behaved similarly in the HAZ.     

ON FATIGUE CRACK PATH DEVIATION AT ELEVATED TEMPERATURE IN ELECTRON BEAM REPAIRED WELDMENTS OF TURBINE DISK

Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are. studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack growth (FCG) rate and crack path deviation (CPD). The base metal served in a turbine disk of aerospace engine was selected to fabricate bead-on-plate weldments by using electron beam welding. Some wedge-type opening loading specimens, notched in three different zone of weld metal, HAZ and base metal, were employed and performed fatigue crack growth tests at 650℃. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, which means that the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strenqth zone.     

TC11钛合金电子束焊接接头超高周疲劳性能

采用天津大学自行研制的TJU-HJ-I型超声疲劳试验系统研究了TC11钛合金电子束焊焊接接头的超高周疲劳性能. 试验结果表明,TC11钛合金电子束焊接接头在107周次以上仍然会发生疲劳失效,S-N曲线呈现连续下降的趋势,没有明显的转折. 试件的断裂位置大多数为母材处,焊缝和热影响区的疲劳性能要比母材好,这与焊接接头的微观组织有关. 通过SEM对超声疲劳断口形貌进行观察发现,断裂试件的疲劳裂纹大部分在表面萌生,然而在应力范围较低时,疲劳裂纹的萌生位置有从表面转向次表面的趋势.     

温度峰值影响6061铝/AZ31B镁异种材料FSW接头成形的规律

以6061-T6铝合金与AZ31B镁合金为研究对象,基于Abaqus软件进行了异种材料搅拌摩擦焊过程的温度场数值模拟,重点分析搅拌针偏置镁侧下的搅拌区温度峰值影响焊缝表面成形的规律。结果表明,当焊接温度峰值高于Al-Mg共晶温度时,搅拌针根部附近区域会出现较明显的黏着现象,其随着焊接速度的降低而加剧,这与焊接温度峰值的升高相关。随着焊接速度的增加,焊缝表面更易避免裂纹缺陷的产生。当搅拌头的转速为1200r/min且焊接速度为40mm/min时,6061铝/AZ31B镁异种材料焊接接头的表面成形良好。     

Fatigue characteristics of patch plate joints by fillet welding assisted with bonding

A series of fatigue experiments and elastic analysis were carried out for investigating fatigue characteristics of patch plate joints assembled by fillet welding assisted with bonding. In the case that fatigue cracks occurred at the weld toe by the four-point bending fatigue experiment, the fatigue life of joints assembled by welding and bonding (WB) specimens were almost the same as those by only welding (W) specimens. The elastic analysis simulating the four-point bending loaded situation on W and WB specimens was performed for elucidating its reason. The stress concentration at the weld toe was even high in the WB specimens. Therefore, the fatigue life of WB specimens was not longer than that of W specimens. On the other hand, the stress around the weld root of WB specimen was around 30% of that of W specimen. The possibility of stress reduction effect by bonding was indicated around the weld root rather than around the weld toe. In order to verify this possibility, the four-point bending fatigue experiment was performed by setting the specimens so that the tensile stress was applied on the weld root. It was confirmed that the fatigue cracks occurred from the weld root in both W and WB specimens. The fatigue life defined in this study of WB specimens was from 4 to 8 times longer than that of W specimens when the applied nominal stress range was under 175 MPa. The fatigue life defined in this study of WB specimens was from 2 to 3 times longer than that of W specimens when the applied nominal stress range was over 200 MPa. The results indicated the fatigue life improvement of patch plate joints by fillet welding assisted with bonding when the fatigue cracks occurred at the weld root.     

TA15钛合金电子束焊焊接接头力学性能

钛合金材料以及相关制造技术是实现飞机先进性的重要基础之一,电子束焊接是钛合金板材一种先进的焊接形式.对TA15钛合金板材电子束焊接试样进行了金相分析和静力试验、疲劳试验和扫描电镜(SEM)分析.结果表明,TA15板材电子束焊焊接接头的焊缝、热影响区和母材的微观组织差别明显;焊缝韧性降低,抗拉强度高于母材;热影响区尺寸较小,在1～2 mm左右,是焊接接头的薄弱部位;疲劳裂纹大多萌生于焊接热影响区区域,疲劳破坏试样断口的SEM分析表明,疲劳裂纹大多起源于焊接热影响区的气孔处.     

不同返修次数对6082-T6铝合金对接接头疲劳性能的影响

对不同返修次数的高速列车用6082-T6铝合金搅拌摩擦焊对接接头进行脉动拉伸疲劳试验,并对疲劳断口进行扫描观察与分析。结果表明,焊接接头指定寿命为1×107次的中值疲劳极限随返修次数的增加而升高。搅拌摩擦焊返修两次时焊接接头的疲劳极限强度较高,疲劳试验中的试件断裂位置主要集中在背面焊缝边缘。启裂区和扩展区疲劳纹清晰,终断区为浅韧窝型韧性断口。