添加钛粉对铝合金搅拌摩擦焊接头晶粒结构热稳定性的影响

利用搅拌摩擦焊接过程中产生的瞬时高温和强烈材料变形,通过内部开槽的方式引入铝钛混粉,使得铝与钛在焊接过程中发生剧烈原位反应,并生成金属间化合物颗粒. 探讨焊核内部的第二相分布与焊后热处理过程晶粒结构稳定性之间的关系. 结果表明,在6061铝合金中,添加钛粉的焊后热处理样品,异常晶粒区域面积大幅减小. 这说明通过引入第二相颗粒的方式,有效地抑制了焊后热处理所产生的异常晶粒长大现象;并且随着焊接道次数的增加,残留钛颗粒的分布逐渐弥散,异常晶粒长大抑制效果愈加明显,提升了焊核区域晶粒结构的热稳定性.     

The effect of welding parameters on the corrosion behaviour of friction stir welded AA2024-T351

The effect of welding parameters (rotation speed and travel speed) on the corrosion behaviour of friction stir welds in the high strength aluminium alloy AA2024-T351 was investigated. It was found that rotation speed plays a major role in controlling the location of corrosion attack. Localised intergranular attack was observed in the nugget region for low rotation speed welds, whereas for higher rotation speed welds, attack occurred predominantly in the heat-affected zone. The increase in anodic reactivity in the weld zone was due to the sensitisation of the grain boundaries leading to intergranular attack. Enhancement of cathodic reactivity was also found in the nugget as a result of the precipitation of S-phase. The results were compared with samples of AA2024-T351 that had been heat treated to simulate the thermal cycle associated with welding, and with samples that had been exposed to high temperatures for extended periods to cause significant over-ageing.     

Microstructural characterisation of double pulse resistance spot welded advanced high strength steel

The effects of single and double pulse resistance spot welding on the microstructures of an advanced high strength automotive steel are presented in this work. The double pulse welding schemes partially remelt the primary weld nugget and anneal the area at the fusion boundary of the nugget. The effects of the annealing treatment on the segregation and the microstructure have been studied by electron probe microanalysis (EPMA) in combination with electron backscatter diffraction (EBSD). Results show that phosphorus has been redistributed at the primary weld nugget edge of the double pulse welds, while the mean block width and ellipticity of the prior austenite grains were smaller in welds subjected to double pulsing compared with single pulse weld. A favourable failure mode was obtained for the double pulse welds although behaviour did not correlate with the measured grain size.     

Structure-Property Correlation of AA2014 Friction Stir Welds: Role of Tool Pin Profile

The influence of rapid plastic deformation in the generation of welding heat during friction stir welding (FSW), supplementing the frictional heat generation by the tool shoulder, forms the thrust of the present investigation. Several researchers have highlighted the role of tool shoulder in the generation of frictional heat and suggested that the tool-material interface friction as the sole mechanism for heating. The configuration of tool pin profile is seldom studied for its contribution to welding heat through rapid plastic deformation at high strain rates (10³/s), especially while welding thick plates. An attempt has been made to understand the dependence of deformation heat generation with different tool pin profiles in welding 5 mm thick AA2014-T6 aluminum alloy, maintaining the same swept volume during the tool rotation. An attempt has also been made to correlate the influence of process response variables such as force and torque acting on the tool pin. To quantify the physical influence of tool pin profile, temperature measurements were made in the region adjacent to the rotating pin, close to nugget in the thermo-mechanically affected zone (TMAZ). It has been observed that the temperature rises at a relatively rapid rate in the case of hexagonal tool pin compared to the welds produced employing other tool pin profiles. It is observed that during FSW, extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the mechanical properties of the joint. The present study is also aimed at understanding the influence of tool profile on the microstructural changes and the associated mechanical properties. Transverse tensile samples failed at the nugget/TMAZ boundary due to localized softening. Hexagonal tool pin profile welds have shown higher tensile strength, low TMAZ width, and high nugget hardness compared to other tool pin profile welds.     

搅拌摩擦焊接工艺参数对AA6061-B4C焊接接头抗拉强度的影响（英文）

搅拌摩擦焊(FSW)是一种固态连接技术,可用来连接高强度铝合金及多种陶瓷颗粒增强金属基复合材料(MMCs)。搅拌摩擦焊获得的陶瓷增强金属基复合材料焊缝优良,在增强体与基体间没有发生有害反应。对搅拌摩擦焊接工艺参数对AA6061-B4C焊接接头抗拉强度的影响进行研究。采用4因素5水平的中心复合设计来控制实验的次数。构建一数学模型来分析搅拌摩擦焊工艺参数对接头抗拉强度的影响。结果表明,在旋转速度1000r/min、焊接速度1.3mm/s、轴向力10kN、增强相含量12%的条件下,搅拌摩擦焊得到的焊接接头的抗拉强度最大。根据构建的模型采用广义简约梯度算法进行优化以得到最大的抗拉强度。金相分析表明,在焊接接头中出现了多种区域,如焊合区、热力影响区和热影响区。在焊合区观察到大量的被细化的铝基体晶粒以及粒径明显减小的B4C颗粒。在热力影响区出现塑性变形、热影响和被拉长的铝晶粒。     

Effect of Friction Stir Welding on Pitting and Stress Corrosion Cracking Behavior of AFNOR7020-T6 Aluminium Alloy

Present work mainly focused on the pitting and stress corrosion cracking behavior of AFNOR7020 aluminium alloy friction stir welds and compared those results with the base material. Initially, microstructural studies, TEM, microhardness tests, tensile tests and general corrosion properties of the welds were investigated. The elongated grains present in the base material have been transformed into superfine grains in the weld nugget. Transmission electron micrographs obtained from various regions of the weld indicated that almost all strengthening precipitates dissolved in the nugget region while partial dissolution of precipitates occurred in the thermo-mechanically affected zone and coarsening occurred in heat affected zone. Hardness in the weld nugget was found to be very nearer to the base material without considerable difference. The welds showed superior joint efficiency of 85% in terms of the yield strength and 95% in terms of ultimate tensile strength. General corrosion resistance of the welds was better than that of the base material at different pH value and spraying time. Pitting corrosion studies revealed that less significant difference in pitting corrosion resistance has been observed between the weld nugget and the base material. It was found that the susceptibility towards stress corrosion cracking is relatively more in base metal compared to welded joints. It has been concluded that friction stir welding plays a very important role in corrosion properties of the AFNOR7020 aluminium alloy.     

Effect of tool rotation rate on microstructure and mechanical properties of friction stir welded copper

Abstract

Defect free copper welds were achieved by friction stir welding (FSW) carried out at a constant welding speed of 100 mm min^?1. The influence of tool rotation rate on microstructure, mechanical properties and fracture location was investigated. As the tool rotation rate increased, the grains of nugget zone grew significantly, the thermomechanically affected zone became indistinct and the grain size increased, but the effect of tool rotation rate on the grain size of heat affected zone was limited. Both ultimate tensile strength (UTS) and elongation increased first and then decreased with increasing rotation rate and the UTS achieved a highest value of 282 MPa at the rotation rate of 400 rev min^?1 together with the welding speed of 100 mm min^?1, which was on the level of the base metal. The fracture occurred at the cavity defect on the advancing side of the joint when the FSW was performed at a low tool rotation rate, while it occurred on the retreating side when the tool rotation rate was relatively high.     

H62黄铜搅拌摩擦焊接头微观结构及性能

对6 mm厚度的H62黄铜搅拌摩擦焊(FSW)焊缝的微观组织、力学性能进行了研究,测试并比较了焊缝和母材金属的动电位和电阻率在热-力作用下的变化.结果表明,焊缝金属经热和机械力的作用后,焊核区、热力影响区和热影响区的平均晶粒尺寸较母材的35.6μm均有细化,依次为3.8,22.2,30.6μm,反应在力学性能上焊核区硬度最高,拉伸断裂发生在硬度较低的前进侧,在微观断口中存在大量尺寸不均的网状韧窝;焊缝的腐蚀电位较母材有所提高,腐蚀电流密度降低,电阻率高于母材.     

Microstructures and properties of friction stir spot welded DP590 dual phase steel sheets

DP590 steel sheets were joined by friction stir spot welding using polycrystalline cubic boron nitride tool with an objective to produce bond diameters similar to conventional spot welding nuggets. A range of spindle rotation (400–2400 rev min^?1) and plunge speeds (0·03–3·8 mm s^?1) were exercised to attain defect free welds in 1·6 mm thick sheets. A bond diameter of 4t^1/2, alike minimum nugget diameter criteria for resistance spot welds, resulted in superior mechanical properties than conventional spot welds. The heat inputs corresponding to different welding parameters influenced the weld microstructure, including grain size, phases and their morphology. The bond diameter was higher for higher heat inputs. However, low heat input welds with weld time cycles ～4 s produced more refined microstructure and exhibited similar strengths even with reduced bond size. Plug type failure was associated with larger bond diameters (～7·1 mm), while interfacial failure was observed with smaller welds (～5·4 mm).     

Microstructure–properties relationships in martensitic stainless steel resistance spot welds

The paper addresses the phase transformations and mechanical response of martensitic stainless steel resistance spot welds. The fusion zone microstructure consists of carbon-rich martensite together with a relatively high amount of retained delta ferrite along the grain boundaries with a transition in solidification mode from equiaxed to columnar dendritic grains across the fusion zone. The heat affected zone microstructure is featured by martensitic matrix together with carbide precipitation. The very high hardness of the fusion zone and the heat affected zone, the sharpness of the notch at sheet/sheet interface, which is located in the hard microstructural zone, and the presence of delta ferrite in the weld nugget play important roles in failure characteristics and mechanical performance of the joint.     

Evaluation of heat input during friction stir welding of aluminium alloys

Heat input is one of the key parameters governing the quality and service properties of friction stir welds. By using a calorimetric technique, the heat inputs generated during the friction stir welding of the aluminium alloys, 1100 and 5083, were measured over a wide range of welding parameters. An empirical equation to estimate the heat input using the welding parameters was established based on a multiple regression analysis of the results. The effect of the heat input on the final grain size of the stir zone was also investigated by the electron backscatter diffraction method. The quantitative relationships between the input variables, heat inputs, and final grain sizes in the stir zone were derived.     

400MPa级细晶粒钢电阻点焊接头组织分析

以智能型点焊机为试验平台,研究超级钢点焊接头的组织和显微硬度分布情况.结果表明,普通低碳钢的点焊工艺不适用于超级钢,需附加锻压力,以消除气孔等收缩性缺陷.熔核内部组织结构分别为等轴晶区和胞状晶区;熔核外部的热影响区包括过热区和重结晶区.接头区域的显微硬度明显高于母材组织,主要是由于点焊快冷条件下产生了马氏体组织;而热影响区的组织硬度稍低于熔核中心区域,应是残余应力及再生细晶相互作用的结果.     

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.     

Nb含量和热输入量对X80管线钢焊接粗晶区的影响

以工业含铌X80管线钢为对象,研究了不同Nb含量条件下,焊接热影响区粗晶区中的原奥氏体晶粒和析出的状态;通过对焊接热影响区中粗晶区的热模拟实验,研究了不同热输入下,高Nb管线钢焊接粗晶区的晶粒粗化、显微组织演变、及大角晶界分布等情况。结果表明,高Nb钢的粗晶区范围更窄,粗晶区内的晶粒尺寸更小;经过双道焊的热循环后,高Nb钢粗晶区的析出尺寸更小,没有对韧性有害的大尺寸析出。此外,原奥氏体晶粒的粗化,以及显微组织中大角晶界密度的下降,明显降低了高Nb管线钢焊接粗晶区的韧性。     

镁-钢异种金属无匙孔搅拌摩擦点焊过程分析

在最优焊接参数下,对AZ31B镁板和DP600镀锌钢板进行无匙孔搅拌摩擦搭接点焊试验,得到剪切力达到8.7 k N的接头.整个点焊过程分为插入(I)、搅拌与回抽(II)、回抽完毕(III)三个阶段.显微组织分析表明,焊核区,钢的晶粒细长,流向明显.热力影响区,钢和镁合金均发生动态再结晶,钢的晶粒粗长,镁合金晶粒最为粗大,但在搅拌针回抽区域,镁合金晶粒细小且分布均匀,全部为再结晶等轴晶粒.热影响区,钢的晶粒更为粗长,镁合金的晶粒也较为粗大.接头主元素分析表明,(I)阶段,镁与钢的界面没有发生扩散;(II),(III)阶段,在焊核区主元素之间发生了扩散.     

2A14-T4铝合金T形接头静轴肩搅拌摩擦焊组织结构与力学性能

采用静轴肩搅拌摩擦焊接法（SSFSW）在不同的焊接速度下制备了2A14-T4铝合金T形接头。在优化的焊接工艺参数下,可以得到光滑的T形接头焊缝表面。结果表明：焊接熔核区（WNZ）的显微组织为完全动态再结晶产生的细小等轴晶,第2次焊核区（WNZ2）的平均晶粒尺寸最大,焊接重合区（WNOZ）次之,第1次焊核区（WNZ1）的平均晶粒尺寸最小。WNZ的再结晶机制主要是几何动态再结晶,并伴有部分连续动态再结晶。WNZ1和WNZ2织构类型为弱{111}<110>,而WNOZ经过2次搅拌后织构类型为弱{100}<001>。热机械影响区（TMAZ）发生塑性变形,而热影响区（HAZ）只受到焊接热循环作用,不发生塑性变形和晶粒的动态再结晶。WNZ的硬度较高,硬度最低的区域位于靠近TMAZ的HAZ。随着焊接速度的增加,接头抗拉伸强度先增大后减小。底板和加强板的主要断裂形式是脆性/韧性混合断裂。     

Grain characteristic and texture evolution in friction stir welds of nanostructured oxide dispersion strengthened ferritic steel

Abstract

The present paper investigated the grain and texture characteristics in a nanostructured oxide dispersion strengthened ferritic steel subjected to friction stir welding. The ‘onion rings’ structure obviously exhibited in the macrostructure overview of the welds. The electron backscatter diffraction (EBSD) work revealed that the ‘onion rings’ comprised alternate layers made by coarse and fine grains, while no strong texture was exhibited in the alternate layers of the ‘onion rings’. Image quality maps of EBSD indicated that layers of fine grains were deformed under high strain conditions. Textures within the stir zone and thermomechanically affected zone were weak and exhibited some characteristics of bcc simple shear textures. Results of grain boundary revealed that the mechanical action in welding process promoted the transformation of low angle to high angle boundaries and contributed to the grain refinement.     

Material flow and microstructure in the friction stir butt welds of the same and dissimilar aluminum alloys

The material flow and microstructural evolution in the friction stir welds of a 6061-Al alloy to itself and of a 6061-Al alloy to 2024-Al alloy plates of 12.7 mm in thickness were studied under different welding conditions. The results showed that plastic deformation, flow, and mechanical mixing of the material exhibit distinct asymmetry characteristics at both sides of the same and dissimilar welds. The microstructure in dissimilar 6061-Al/2024-Al welds is significantly different from that in the welds of a 6061-Al alloy to itself. Vortex-like structures featured by the concentric flow lines for a weld of 6061-Al alloy to itself, and alternative lamellae with different alloy constituents for a weld of 6061-Al to 2024-Al alloy, are attributed to the stirring action of the threaded tool, in situ extrusion, and traverse motion along the welding direction. The mutual mixing in the dissimilar metal welds is intimate and far from complete. However, the bonding between the two Al-alloys is clearly complete. Three different regions in the nugget zone of dissimilar 6061-Al/2024-Al welds are classified by the mechanically mixed region (MMR) characterized by the relatively dispersed particles of different alloy constituents, the stirring-induced plastic flow region (SPFR) consisting of alternative vortex-like lamellae of the two Al-alloys, and the unmixed region (UMR) consisting of fine equiaxed grains of the 6061-Al alloy. Within all of these three regions, the material is able to withstand a very high degree of plastic deformation due to the presence of dynamic recovery or recrystallization of the microstructure. The degree of material mixing, the thickness of the deformed Al-alloy lamellae, and the material flow patterns depend on the related positions in the nugget zone and the processing parameters. Distinct fluctuations of hardness are found to correspond to the microstructural changes throughout the nugget zone of dissimilar welds.     

轴肩辅助加热6082铝合金摩擦塞补焊接头组织及力学性能

为了解决搅拌摩擦焊匙孔类体积型缺陷修复问题,在填充式搅拌摩擦焊基础上,采用轴肩与母材摩擦辅助加热的方法对同种材料铝合金匙孔类缺陷进行摩擦塞补焊,在不同的塞棒转速下得到了成形良好的塞补焊接头.?结果表明,由于热输入和材料形变作用,接头不同区域组织发生了明显变化.?不同塞棒转速下接头组织及分布状态相似.?一个完整的塞补焊接...     

Friction stir weld nugget temperature asymmetry

Abstract

Two different hardness distributions were observed to result from the friction stir welding of an Al–Mg–Si alloy using identical welding speeds but different heat inputs. In one case, the distribution was relatively symmetric about the weld centreline and in the other, the hardness declined continuously from the advancing to the retreating sides of the weld nugget. Based on in-probe temperature measurements, full-field grain size mapping, and response to post-weld heat treatment, it has been ascertained that under low heat input conditions, the weld nugget attained a higher temperature on the advancing side than on the retreating side. Such a temperature asymmetry has often been proposed and has been predicted by simulation but, has not been convincingly demonstrated before this time.