Al-Li-Cu合金搅拌摩擦焊与TIG 焊接头组织及力学性能分析

组织分析表明,Al-Li-Cu TIG焊焊缝和搅拌摩擦焊焊核区均由等轴晶粒构成,但前者的晶粒尺寸较后者的大;TIG焊接头热影响区组织粗化程度较搅拌摩擦焊严重;搅拌摩擦焊接头内存在一独特的热机影响区,该区内的组织发生了较大程度的变形。实验结果表明铝锂合金搅拌摩擦焊可避免形成TIG焊时的凝固裂纹等缺陷。搅拌摩擦焊接头的力学性能优于TIG焊接头,二者的拉伸强度分别为393MPa和337MPa,延伸率分别为14．4％和6．6％。     

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy(Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance.Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys,friction stir welding(FSW) process is an emerging solid state joining process in which the material welded does not melt and recast.Joint strength is influenced by the grain size and tensile strength of the weld nugget region.Hence,an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints.The empirical relationships are developed by response surface methodology(RSM) incorporating FSW tool and process parameters.A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.     

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.     

2219铝合金搅拌摩擦焊接接头剥落腐蚀机理

采用原位腐蚀试验、静态失重试验、浸泡试验研究了2219铝合金搅拌摩擦焊接接头的剥落腐蚀行为与机理。结果表明:2219铝合金搅拌摩擦焊焊缝腐蚀速率比母材小,焊缝的抗腐蚀性提高;腐蚀从局部点蚀开始,起源于第二相粒子与其边缘的铝基体,第二相粒子作阴极;原位腐蚀2 h后焊核与热机影响区发生晶间腐蚀,母材发生严重的点蚀;均匀分布的第二相粒子与细小的等轴晶组织是焊核区剥落腐蚀敏感性降低的主要原因。     

超声对不同铝合金搅拌摩擦焊接头性能的影响

利用自行研制的超声搅拌摩擦焊机分别对2219,7A52,LF21铝合金进行了常规搅拌摩擦焊和超声搅拌摩擦焊两种不同焊接的试验,并对常规搅拌摩擦焊与超声搅拌摩擦焊焊缝的微观组织、拉伸断口形貌进行了对比分析.结果表明,超声搅拌摩擦焊与常规搅拌摩擦焊相比热影响区几乎消失;超声搅拌摩擦焊焊缝焊核区组织比常规搅拌摩擦焊焊核区组织晶粒更加细小;断口扫描电镜图显示母材断口韧窝具有非等轴状待征,韧窝边上撕裂棱明显表明为韧性断裂;超声搅拌摩擦焊断口韧窝撕裂棱不明显;超声搅拌摩擦焊比常规搅拌摩擦焊的平均抗拉强度有所提高,但断后伸长率有所降低.     

30 mm 7A05铝合金搅拌摩擦焊接头组织及力学性能

采用搅拌摩擦焊方法利用新型搅拌头对30 mm厚的7A05-T6铝合金进行了单道对接,焊后分析讨论了焊缝接头微观组织和力学性能.结果表明,接头焊核区发生动态再结晶,生成细小的等轴晶粒;焊缝两侧热力影响区受机械和热的双重作用,组织存在较大差异,前进侧为窄条状组织,后退侧为扁平状组织;热影响区晶粒粗化;在焊接30 mm板时,工艺参数范围较窄,旋转频率为360 r/min,焊接速度为100 mm/min时,可获得无缺陷、成形好的焊缝;接头抗拉强度为367.7 MPa、屈服强度为280.8 MPa、断后伸长率为14.4%高于母材,接头抗拉强度可达母材的95%.接头显微硬度的分布呈类似W形分布,热影响区软化趋势比较明显.     

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.     

35mm厚板铝合金搅拌摩擦焊接头组织和性能

采用搅拌摩擦焊双面焊工艺,对35 mm厚板6005A-T6铝合金型材进行了搅拌摩擦焊接,获得成形良好、表面光滑、无隧道孔和沟槽缺陷的焊接接头.应用光学显微镜、扫描电镜、显微硬度仪及电子拉伸试验机等对搅拌摩擦焊接头组织与性能进行研究.结果表明,接头焊核区组织为细小等轴晶;前进侧出现明显的螺旋纹及清晰的结合线,热力影响区晶粒被明显拉长呈条状组织,热影响区受热晶粒粗大;后退侧未见螺旋纹,晶粒比前进侧细小,过渡区较前进侧宽.在搅拌头旋转频率为650 r/min,焊接速度为200 mm/min工艺条件下接头抗拉强度为213 MPa,达到母材强度的84.8%,断裂起始于焊缝前进侧的热影响区,扩展至双面焊接重合区时,沿着焊缝后退侧热影响区直至断裂;接头显微硬度最低值出现在前进侧热影响区,最低值为50 HV.     

超声振动对6061-T4铝合金搅拌摩擦焊接头组织和性能的影响

利用自主研制的试验装置,通过工具头将超声振动能量施加在搅拌头前方的待焊工件上,研究了超声振动能量对减少焊接缺陷、改善搅拌摩擦焊接头组织和力学性能的影响.对6 mm厚度6061-T4铝合金板进行了超声振动强化搅拌摩擦焊工艺试验,并与相同工艺条件下的常规搅拌摩擦焊进行了对比.结果表明,超声振动能够减小焊速/转速比较大时的焊缝内部隧道型缺陷,增大材料对接混合区宽度和焊核区体积,细化焊核区和热力影响区微观组织,提高接头抗拉强度和焊核区显微硬度.     

2219-O铝合金的搅拌摩擦焊接

对2219-O铝合金进行了搅拌摩擦焊接,采用光学显微镜分析了接头的微观组织,采用拉伸试验方法评价了接头的力学性能.微观分析表明,在热机循环的共同作用下,焊核区(WNZ)发生了动态再结晶,形成了细小的等轴晶粒,并且沉淀相的数量较其它各区有所增加;热机影响区(TMAZ)晶粒被拉长、弯曲,发生了动态回复和部分再结晶,晶粒内部开始有新的晶粒生成;热影响区(HAZ)的晶粒发生粗化.力学性能测试结果表明,当转速为800r/min,焊接速度为200～400 mm/min时,接头与母材等强度,断裂发生在母材区;当焊接速度大于400mm/min时,接头的抗拉强度很低,断裂发生在缺陷处.     

Macrostructures and mechanical properties of ultrasonic-assisted friction stir welding joint of 2024-T3 aluminium alloy

In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection of friction stir welding tool and process parameters. Ultimately, such defects degrade the properties of weld and may pose serious concerns towards the integrity and safety of the weld component. In order to improve the properties of weld joints, an ultrasonic-assisted friction stir welding device has been configured where ultrasonic energy is transferred from an ultrasonic unit directly into one of the workpieces near the tool. Using this configuration, ultrasonic-assisted friction stir welding was conducted on 6 mm thick 2024-T3 aluminum alloy sheets. The macrostructure and mechanical properties of these welds were compared with the welds of this alloy prepared by conventional friction stir welding using identical process parameters. The results show that the welding speed can be increased while satisfactory weld quality is still ensured. The ultrasonic energy transferred in this configuration could enlarge the volume of weld nugget zone. Also, the influence of ultrasonic energy on the suppression or elimination of the tunnel defect is quite apparent. However, any beneficial effects of ultrasonic vibration on the tensile strength and the elongation of the joint were less obvious in this configuration.     

6005A铝合金搅拌摩擦焊接头的晶间腐蚀行为

对6005A铝合金搅拌摩擦焊接头的晶间腐蚀行为进行了研究.结果表明,母材的晶间腐蚀倾向最大,热影响区(HAZ)次之,焊核区(NZ)和热力影响区(TMAZ)的晶间腐蚀倾向最低.结合场发射扫描电镜、高分辨透射电镜分析解释了接头不同区域的腐蚀行为:母材的晶间腐蚀是两组微电池效应的结果,即晶界析出相/沉淀无析出带(PFZ)和铝基体/PFZ;HAZ内晶界析出相的数量的减少、间距的变大及晶内Q'相的析出显著改善了该区的晶间腐蚀性,但晶内Q'相的析出也引起了点蚀的发生;NZ和TMAZ内绝大部分的合金元素固溶于基体,抑制了晶间腐蚀的发生.     

Modelling microstructural evolution during multiple pass friction stir welding

Abstract

The effect of multiple weld passes on the microstructure and properties of friction stir welds in aerospace aluminium alloy AA 7050 has been investigated with the aid of a microstructure model. Each weld pass leads to a reduction in minimum strength in the heat affected zone, the decrease being greatest after the first pass. The model predicts that this is due to partial dissolution and coarsening of the strengthening precipitatates, which up to weld pass 3 is dominated by dissolution, and beyond weld pass 3 by coarsening. Microstructural evolution in the nugget is predicted to involve complete precipitate dissolution during each pass, followed by reprecipitation on the refined grain boundaries. A post-weld aging treatment after multiple passes is predicted not to be effective in improving minimum strength since precipitation occurs via growth and coarsening of existing particles, not nucleation of new precipitates.     

Tungsten Inert Gas and Friction Stir Welding Characteristics of 4-mm-Thick 2219-T87 Plates at Room Temperature and −196 °C

2219-T87 aluminum alloy is widely used for fabricating liquid rocket propellant storage tank, due to its admirable cryogenic property. Welding is the dominant joining method in the manufacturing process of aerospace components. In this study, the tungsten inert gas welding and friction stir welding (FSW) characteristics of 4-mm-thick 2219-T87 alloy plate at room temperature (25 °C) and deep cryogenic temperature (?196 °C) were investigated by property measurements and microscopy methods. The studied 2219 base alloy exhibits a low strength plane anisotropy and excellent room temperature and cryogenic mechanical properties. The ultimate tensile strength values of TIG and FSW welding joints can reach 265 and 353 MPa at room temperature, and 342 and 438 MPa at ?196 °C, respectively. The base metal consists of elongated deformed grains and many nano-scaled θ (Al₂Cu) aging precipitates. Fusion zone and heat-affected zone (HAZ) of the TIG joint are characterized by coarsening dendritic grains and equiaxed recrystallized grains, respectively. The FSW-welded joint consists of the weld nugget zone, thermo-mechanically affected zone (TMAZ), and HAZ. In the weld nugget zone, a micro-scaled sub-grain structure is the main microstructure characteristic. The TMAZ and HAZ are both characterized by coarsened aging precipitates and elongated deformed grains. The excellent FSW welding properties are attributed to the preservation of the working structures and homogenous chemical compositions.     

Al-Zn-Mg铝合金厚板搅拌摩擦焊接头组织与分层性能

采用搅拌摩擦焊方法对14 mm厚Al-Zn-Mg铝合金进行对接焊接,研究了沿厚度方向分层切片的横向拉伸和应力腐蚀性能,揭示搅拌摩擦焊接头分层力学和腐蚀性能的不均匀性。研究结果表明,焊核区为细小的再结晶组织,焊核区从上表层到下表层晶粒尺寸逐渐减小;接头两侧的热影响区存在明显软化区;接头分层的抗拉强度波动较小,在315～330 MPa之间,断裂位置均位于前进侧的软化区;接头上、下表层在四点弯曲试验中均未发生腐蚀断裂,接头上、下表层热影响区的腐蚀敏感性最高;晶内析出相发生粗化和晶界析出相连续分布,是导致热影响区力学性能和耐蚀性能降低的根本原因。     

2219铝合金FSW和TIG焊接头力学与腐蚀行为

评价了2219-CS铝合金FSW和TIG焊接头的力学性能,并采用晶间腐蚀、剥落腐蚀及电化学腐蚀方法对2219-CS铝合金FSW和TIG焊接头进行了整体及分区域腐蚀行为表征,借助光学显微镜和扫描电子显微镜分析了表面腐蚀形貌. 结果表明,搅拌摩擦焊接头焊核区的细晶结构和弥散再分布的沉淀相大幅度提高了其耐腐蚀性能,热影响区中沉淀相回溶及粗化较TIG焊接头热影响区较弱,耐腐蚀性能有一定提高,搅拌摩擦焊接头的高电化学均质性宏观表现为其整体腐蚀速率的显著降低.     

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Abstract

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.     

2A97铝锂合金搅拌摩擦焊

文中采用不同搅拌摩擦焊接工艺参数对2A97铝锂合金的可焊性进行了研究.结果显示,接头抗拉强度和断后伸长率随搅拌头转速的提高而降低,随焊接速度的提高先增后减.在旋转频率为600 r/min,焊接速度200 mm/min时接头抗拉强度最高达到373 MPa,为母材的69%.FSW接头拉伸试验断口位置基本都发生在焊核(NZ)区.焊核区和热力影响区中沉淀相大部分溶解,只有少数存留,热力影响区沉淀相密度高于焊核区.     

2A14-T6铝合金双轴肩搅拌摩擦焊特征及接头组织性能分析

成功实现了2A14-T6高强铝合金的双轴肩搅拌摩擦焊,获得了表面成形良好,无内部缺陷的优质接头. 试验发现,在焊缝的焊核内存在一个由上、下轴肩和搅拌针所驱动的材料塑性流动交汇区,该交汇区靠近焊缝下表面. 微观分析表明,焊核上部的晶粒尺寸要小于其中部和下部的晶粒尺寸. 焊缝各区的块状第二相在焊接中发生了溶解和粗化,导致接头内出现了宽度近乎轴肩直径二倍的软化区;焊缝各层硬度分布接近,没有出现常规搅拌摩擦焊中常见的接头各层异性现象. 经拉伸测试证实,双轴肩焊接接头的强度系数达到了71%,拉伸时断在了焊核内的材料流动交汇区处.     

Effect of second-phase particle on localized corrosion in Al–Zn–Mg–Cu–Mn alloy friction stir welded joint

The microstructure and corrosion behavior of a high-strength Al–Zn–Mg–Cu–Mn alloy friction stir welded (FSWed) joint were investigated using scanning electron microscope, transmission electron microscope, open-circuit potential test, and potentiodynamic polarization. The weld nugget zone and heat-affected zone (HAZ) of the FSWed joint showed diverse microstructural characteristics including micron-scale intermetallic particles and nanoscale precipitates, leading to different localized corrosion sensitivities. The results of electrochemical tests confirmed the regional difference of corrosion in FSWed joints. Detailed research on the corrosion process revealed that micron-scale Al(Fe,Mn,Si) particles promoted the dissolution of the vicinal matrix to induce pitting corrosion. The directionally distributed intermetallic particles and grain boundary precipitates in HAZ conduced to the development of intergranular microcracks into exfoliation. The matrix precipitates affected the localized corrosion tendency due to regional variation of the redissolution degree.