7050铝合金回填式搅拌摩擦点焊组织与性能研究

目的 研究2.5 mm厚的7050-T74511铝合金回填式搅拌摩擦点焊工艺参数,焊点组织与力学性能之间的关系。方法 通过显微组织观察和断口扫描,分析接头形貌特征和缺陷对断裂模式的影响。通过拉伸剪切测试,分析工艺参数与力学性能之间的关系。采用三因素三水平BBD响应面法进行工艺优化,建立拉剪失效载荷与工艺参数之间的二阶响应模型并求得最优工艺。结果 工艺优化的最佳参数为扎入深度2.7 mm,焊具转速为1500 r/min,焊接时间为8 s,在此参数下接头拉剪失效载荷为8.294 kN。当焊接工艺参数选择恰当时,可得到无缺陷接头。结论 焊接工艺窗口较窄;在高热输入条件下（扎入深度3.1 mm,转速2100 r/min）易产生孔洞、弱连接等缺陷,且这些缺陷主要分布在搅拌区与热力影响区界面上;在低热输入条件下（扎入深度2.7 mm,转速1500 r/min）,接头拉剪载荷较高,这与焊点在低热输入情况下组织缺陷较少有关。     

铝合金薄板搭接高速 FSW 缺陷及断裂行为

目的 为了拓展搅拌摩擦焊技术应用,对薄板搭接结构高速搅拌摩擦焊工艺优化与工程应用提供 借鉴与指导。方法 采用圆锥无螺纹搅拌针,进行了 6061 铝合金薄板搭接高速搅拌摩擦焊接,对接头界 面缺陷及其断裂模式进行分析,探讨了转速对 6061 铝合金薄板搭接接头成形及性能的影响规律。结果 发现在无螺纹圆锥搅拌针、高转速（6000~9000 r/min）条件下,接头塑性金属在后退侧易形成飞边流出, 导致下板前进侧出现孔洞缺陷,且随转速增大,界面缺陷尺寸逐渐增大,当转速达到 10 000 r/min 时, 孔洞尺寸有所减小,此时接头拉剪强度最高,为 123 MPa。对试样拉剪断裂位置分析发现,高速搭接接 头断裂位置主要有两种,分别断裂在结合界面处或在前进侧下板,且转速在 9000 r/min 以上越趋向于在 结合界面断裂。结论 高转速搭接焊接必须协调轴肩相貌、焊接工装约束等条件,保证接头塑性金属充 分流动而不流失,才能获得成形良好无缺陷的接头。     

回填式搅拌摩擦点焊热输入对界面孔洞与力学性能的影响

目的 提高焊接热输入及接头力学性能,研究回填式搅拌摩擦点焊的最佳焊接工艺参数。方法 在传统搅拌摩擦点焊产热基础上,结合回填式搅拌摩擦点焊搅拌头具体运动形式,将产热功率对时间进行积分,得到热输入解析方程,测得不同热输入下接头孔洞大小与力学性能,获得热输入对界面孔洞大小与力学性能的影响规律。结果 在其他焊接参数不变的条件下,随着转速由2000 r/min提高至2300 r/min,焊接热输入由54 kJ增加至62 kJ,孔洞面积由9.3×104 μm2迅速减小至7.7×103 μm2,接头拉剪强度由3.2 kN提升至7.2 kN。当转速进一步提高至2600 r/min时,热输入达到70.2 kJ时,孔洞的缩减速率与拉剪强度提升速率减缓,孔洞大小减小至3.8×103 μm2,拉剪强度减小至8.4 kN。结论 在相同的焊接时间下,接头的热输入随着焊接转速的提升而增加,接头孔洞面积减小,拉剪性能提高。     

异种铝合金回填式搅拌摩擦点焊工艺的研究

目的 研究搅拌头转速和轴套下压量对异质铝合金回填式搅拌摩擦点焊接头的组织及力学性能的影响。方法 采用回填式搅拌摩擦点焊技术对7050铝合金和2524铝合金进行搭接焊试验,焊接完成后利用光镜、体式显微镜、扫描电镜对组织进行观察,另外,测试拉伸剪切载荷和显微硬度分布,最后对断裂行为进行了研究。结果 接头区域可以分为焊核区、热力影响区、热影响区、母材4个区域,焊核区晶粒呈细小等轴状,热力影响区晶粒呈粗大长条状。随搅拌头转速的增大,拉剪载荷降低,当转速为1500 r/min时拉剪载荷值最高,其值为7.499 44 kN。热影响区的显微硬度比母材低,最小值为HV106。接头的断裂方式可以分为剪切型断裂、塞型断裂、剪切-半环型断裂。结论 在一定工艺参数范围内,通过适当降低搅拌头转速能显著提高接头的拉剪载荷,轴套下压量对接头的断裂方式影响显著。     

车用DP600和DC54D涂胶与未涂胶电阻点焊研究

对异种钢不同板厚涂胶与未涂胶DP600双相钢和超低碳DC54D电阻点焊进行了研究。深入分析了不同焊接时间下焊接接头显微组织、显微硬度、拉剪性能及扫描断口。研究结果表明,随着焊接时间的延长,焊点直径增大。当焊接时间为2周波时,热影响区为"半月形",延长焊接时间,熔核形状由"蝶形"转变为"椭型"。由于DC54D对熔核区碳含量的稀释作用,熔核区显微硬度低于热影响区硬度。拉伸-剪切试验中,当焊接时间为13-19周波时,涂胶与未涂胶接头拉剪强度趋于稳定。未涂胶接头的最大拉剪强度为5.45kN,涂胶接头的最大拉剪强度为5.15kN。当焊接电流为9kA、电极压力为2.6kN、焊接时间为13-19周波时,涂胶的焊接接头能得到优异的力学性能,但是比未涂胶接头略差。未涂胶与涂胶接头断裂均发生在DC54D侧。     

5083和6061铝合金异种搅拌摩擦焊接接头的组织和性能

以不同的转速对6 mm厚的5083和6061铝合金进行搅拌摩擦焊接,研究了焊接参数对接头组织和性能的影响。结果表明,控制焊接参数可获得良好的焊接质量,接头强度系数为85%。随着转速的升高5083和6061铝合金的晶粒尺寸都逐渐增大,但是在焊核区内5083铝合金的晶粒尺寸比6061铝合金的小;在6061铝合金一侧的热影响区,随着转速的增加析出相的尺寸和密度都逐渐增大。5组焊接参数的焊接接头的最低硬度区均出现在6061铝合金一侧的热影响区,随着转速的升高接头的最低硬度也逐渐提高;焊接接头均断裂在最低硬度区,且随着转速的升高接头的抗拉强度也逐渐提高。     

SUS304不锈钢点焊与胶焊接头的疲劳强度分析

通过拉剪实验测定1.5mm厚SUS304不锈钢点焊接头、胶焊接头的抗拉强度,并开展疲劳实验,获得不同应力水平下两种接头的疲劳寿命,得到两种接头的载荷-寿命曲线;借助扫描电镜分析接头疲劳失效过程。结果表明:当焊接电流为10.0kA、焊接时间为80ms、电极压力为0.5 MPa时,能获得较好的胶焊接头。在此焊接参数下,点焊接头、未固化胶焊接头和固化胶焊接头的平均失效载荷分别为12 825.5N、10 345.6N、10 022.9N;在疲劳实验载荷-寿命曲线的有限寿命区内,SUS304不锈钢胶焊接头的疲劳强度均大于点焊接头;点焊接头和胶焊接头的疲劳失效形式主要由母材眉状裂纹失效和界面撕裂失效两种形式组成;胶焊接头的疲劳失效过程中,首先是胶层粘接失效,随后疲劳裂纹从板间内表面热影响区边缘萌生,沿板厚与板宽方向扩展直至发生疲劳失效。     

转速对6061铝合金搅拌摩擦搭接焊接头组织和力学性能的影响

目的 研究不同转速条件下6061铝合金搅拌摩擦搭接焊接头组织和力学性能的变化规律,为工程实践应用提供参考。方法 在不同旋转速度（800、1 200、1 500 r/min）下对4 mm厚的6061铝合金进行搅拌摩擦搭接焊实验,固定进给速度和轴肩下压量,研究搅拌头转速对接头宏观组织、微观组织和力学性能的影响。结果 所有接头均没有出现明显缺陷,当转速为1 500 r/min时,搅拌区晶粒尺寸细化明显,最大失效载荷达到母材的75%,上板和下板的硬度曲线都呈“W”形;当转速为800 r/min和1 200 r/min时,下板硬度曲线呈“V”形。随着转速的增大,有效搭接宽度逐渐增大,接头的平均拉剪强度也在增大,所有接头都在前进侧断裂,断裂形式均为拉伸断裂。结论 转速的提升增加了焊接热输入量和机械搅拌作用,促进了有效搭接宽度的增大和晶粒尺寸的细化,但未能改变钩状缺陷的形成及延伸方向。当转速为1500r/min时,热输入量较大,搅拌区范围相对较大,下板存在更大面积的搅拌区,其硬度规律与上板的相似。所有接头均为拉伸断裂,断裂位置在热影响区附近,说明搭接接头连接良好。     

6016-T4铝合金与镀锌IF钢搅拌摩擦焊接头的组织与性能

采用搅拌摩擦焊接对1.2 mm厚的6016-T4铝合金和1.0 mm厚的镀锌IF钢进行搭接试验。通过对接头的力学性能和界面组织进行研究,发现在焊接速度为100 mm/min、旋转速度为800～2 000 r/min的条件下焊缝成形良好,表面无沟槽、孔洞等缺陷;当旋转速度为1 200 r/min时,接头的拉剪强度最高,达到172 MPa,为铝合金母材强度的82%;铝合金硬度值呈"W"型分布,最低值在接头两侧的热力影响区及其与热影响区的交界处,硬度最高值在接头的焊核区,达到69.1HV,镀锌IF钢硬度值呈倒"U"型分布,最高值在焊核区,达到192.3HV;在搅拌针和轴肩的共同作用下,铝和钢搭接接头的界面组织特征呈现机械连接+冶金连接的特点,在搅拌针作用区的两侧界面处各形成一个"钩子"状的结构,扎入铝合金基体中,形成机械连接,钢铝界面处生成的Fe-Al金属间化合物、Al-Zn化合物和Fe-Al的层状组织共同形成冶金连接。     

钢/铝CMT接头熔合面积对接头抗剪强度及破坏模式的影响

针对低碳镀锌钢板与6061铝合金CMT熔钎焊接头熔合面积对其抗剪强度和破坏模式的影响进行研究。结果表明:熔钎焊过程中,随着焊枪相对于搭接接头中心线偏移量的增大,接头的熔合面积逐渐减小,润湿角增大,进而导致接头的抗剪强度逐渐减小,接头的断裂位置由铝熔合区破坏向钢/铝界面层破坏转变。根据实验结果,考虑界面层的失效判据,建立CMT接头拉剪过程的数值模型,讨论熔合面积影响接头抗剪强度及破坏模式的原因。     

Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints

In this paper, the microstructure and mechanical properties of 7075-T6 aluminum alloy joints joined by refill friction stir spot welding (RFSSW) were investigated. The keyhole was refilled successfully, and the microstructure of the weld exhibited variations in the grain sizes in the width and the thickness directions. There existed defects (hook, voids, bonding ligament, etc.) associated to the material flow in the weld. Mechanical properties of the joint have been investigated in terms of hardness and tensile/shear and cross-tension test, and the fracture mechanisms were observed by SEM (scanning electron microscope). The hardness profile of the weld exhibited a W-shaped appearance in the macroscopic level, which reached the minimum at the boundary of the sleeve and the clamping ring. The variation laws between tensile/shear and cross-tension strength and processing parameters were rather complicated. The void in the weld played an important role in determining the strength of the joint. On the whole, the preferable strength can be obtained at lower rotational speed. Shear fracture mode was observed under tensile–shear loadings, and nugget debonding, plug type fracture (on the upper sheet) and plug type fracture (on the lower sheet) modes were observed under cross-tension loadings. It was also observed that the main feature affecting the mechanical properties of the joint is the alclad between the upper and lower sheets and the connecting qualities between the stir zone and thermo-mechanically affected zone.     

The optimisation of process parameters for friction stir spot-welded AA3003-H12 aluminium alloy using a Taguchi orthogonal array

The aim of the present work is to optimise the welding parameters for friction stir spot welded non-heat-treatable AA3003-H12 aluminium alloy sheets using a Taguchi orthogonal array. The welding parameters, such as the tool rotational speed, tool plunge depth and dwell time, were determined according to the Taguchi orthogonal table L9 using a randomised approach. The optimum welding parameters for the peak tensile shear load of the joints were predicted, and the individual importance of each parameter on the tensile shear load of the friction stir spot weld was evaluated by examining the signal-to-noise ratio and analysis of variance (ANOVA) results. The optimum levels of the plunge depth, dwell time and tool rotational speed were found to be 4.8 mm, 2 s and 1500 rpm, respectively. The ANOVA results indicated that the tool plunge depth has the higher statistical effect with 69.26% on the tensile shear load, followed by the dwell time and rotational speed. The tensile shear load of the friction stir spot welding (FSSW) joints increased with increasing plunge depth. Additionally, examination of the weld cross-sections, microhardness tests and fracture characterisation of the selected friction spot welded joints were conducted to understand the better performance of the joints. All the fractures of the joints during tensile testing occurred at stir zone (SZ), where the bonded section was minimum. The tensile shear load and tensile deformation of the FSSW joints increased linearly with increasing the bonded size. The finer grain size in the SZ led to the higher hardness, which resulted in higher fracture strength. When the tensile shear load of the joints increased approximately 3-fold, the failure energy absorption of the joints increased approximately 15-fold.     

Mechanical performance optimization of similar thin AA 7075-T6 sheets produced by refill friction stir spot welding

Refill friction stir spot welding was applied to weld similar thin AA 7075-T6 aluminum alloy sheets in a spot-like joint configuration without a keyhole. The welds were produced using a small tool consisting of sleeve and probe with diameters of 6 mm and 4 mm, respectively. Design of experiment was employed to optimize the welding parameters in terms of the cross tensile strength by using Box Behnken Design. Based on analysis of variance, it can be concluded that plunge depth strongly affects the mechanical performance of the weld. Optimal welding parameters in terms of rotational speed, plunge depth and speed are identified to reach a cross tensile strength of up to 660 N.     

Effects of sleeve plunge depth on microstructures and mechanical properties of friction spot welded alclad 7B04-T74 aluminum alloy

Friction spot welding (FSpW) was applied to join the 7B04-T74 aluminum alloy successfully, and effects of sleeve plunge depth on weld appearance, microstructures and mechanical properties were investigated in detail. When the sleeve plunge depth was larger than 2 mm, a surface indentation with a depth of 0.2 mm should be applied in order to eliminate the defect of annular groove. The tensile shear properties of the joints were dependent on hook geometry, location of alclad layer, and hardness of stir zone (SZ). With increasing the sleeve plunge depth from 2 to 3.5 mm, the hook height increased, the alclad layer downward migrated further and the hardness of SZ decreased. The optimized FSpW joint was obtained when the sleeve plunge depth was 3 mm, and the corresponding tensile shear failure load was 11921 N. Two different failure modes, i.e. shear fracture mode and tensile-shear mixed fracture mode, were observed in the tensile shear tests.     

Mechanical performance of AA6181 refill friction spot welds under Lap shear tensile loading

This study investigates the fracture behaviour of refill friction spot welding welds under shear tensile loading. Overlap joints of 6181‐T4 aluminium were produced in 1.7‐mm sheets by varying the rotational speed from 1900 to 2900 rpm and the welding time from 2 to 3.4 s while keeping the plunge depth constant at 1.75 mm. After shear tensile tests, the samples were analysed using optical microscopy and scanning electron microscopy. The strength of the weld and its ductile/brittle behaviour are associated with the nucleation, growth and propagation of two types of cracks: circumferential cracks and annular cracks. Welds produced with longer welding times (≥3 s) and slower rotational speeds (1900 rpm) had higher strengths, low scattering and high energy absorption prior to failure, while welds produced with short welding times (2 to 2.4 s) resulted in poor joints, especially when they also used high rotational speeds.     

Defect features and mechanical properties of friction stir lap welded dissimilar AA2024–AA7075 aluminum alloy sheets

5 mm-Thick dissimilar AA2024-T3 and AA7075-T6 aluminum alloy sheets were friction stir lap welded in two joint combinations, i.e., (top) 2024/7075 (bottom) and 7075/2024. The influences of process conditions (welding speed and joint combination) on defects (hook and voids) features and mechanical properties of joints were investigated in detail. It was found that the hook deflects largely upwards into the stir zone (SZ) at lower welding speeds (50, 150 mm/min) in both combinations. The process conditions significantly affect the hook geometry which in return affects the lap shear strength. In all 2024/7075 joints, voids appear and the joints fracture from the tip of hook on AS along the SZ/TMAZ (thermomechanically affected zone) interface in lap shear test (tensile fracture mode). In 7075/2024 joints, the hook on RS horizontally extends a large distance into the bottom stir zone at higher welding speeds (225, 300 mm/min). The joints fracture in three modes: shear fracture along the lap interfaces, tensile fracture and the mix fracture of both. In both joint combinations, the lap shear strength generally increases with the increase of welding speed. 7075/2024 Joints show higher failure load than 2024/7075 joints at lower welding speeds while the opposite result appears at higher welding speeds.     

Optimization of process parameters of friction stir spot welding of polycarbonate sheets and morphological analysis

Friction stir spot welding has a great impact on the joining process of thermoplastics. In this work, effects of varying rotational speed, plunge depth, and dwell time were investigated on polycarbonate sheets and a filler sheet was utilized to reduce the keyhole size of friction stir spot welded joints. The welding parameters were arranged according to Taguchi L₉ orthogonal design of experiments to determine the optimum levels of process parameters. Lap shear tests were performed to examine the mechanical properties. Using analysis of variance and signal to noise ratio, influences of each welding parameter on the lap joint shear load were evaluated. According to achieved results, tool rotational speed has the highest effect while plunge depth has minimum effect on the mechanical behavior of friction stir spot welded joints. Optimum process parameters were attained as 1000 min⁻¹ for rotational speed, 10.5 mm of plunge depth, and 40 s of dwell time. Optimized process parameters showed 15 % improvement compared to the initial welding parameters. Cross-sectional appearances of welded samples which play an important role in determining lap joint shear load were analyzed by morphological and visual comparisons. Failure modes of the fractured samples for lowest, moderate and highest lap joint shear loads were also observed.     

Role of plunge depth on the joint formation and mechanical behavior of Al6063-AZ91 dissimilar lap joint produced by friction stir welding

Dissimilar lap joint of Al6063 aluminium and AZ91 magnesium alloys was successfully produced by friction stir welding. Three different plunge depths (3.2 mm, 3.25 mm, and 3.3 mm) were adopted during welding. Similar Al6063–Al6063 lap joints were also produced along with the dissimilar Al6063–AZ91 joints for the purpose of comparing the joint formation. With the increased plunge depth, the width of the similar Al6063 - Al6063 lap joint was increased. On the contrary, joint width was decreased for the dissimilar joint with increased plunge depths. The dissimilar joint was formed with a strong metallurgical bonding between the Al6063 and AZ91 alloys, which is attributed to the mechanical mixing of these alloys in the nugget zone. Additionally, the formation of intermetallics was also observed from the x-ray diffraction analysis. The variations within the measured hardness values were higher at the joint interface due to the mixing of aluminium and magnesium alloys in the nugget zone. From the tensile shear tests, increased strength and decreased elongation were measured with the increased plunge depth. The results demonstrate the importance of the plunge depth on the lap joint formation between dissimilar Al6063–AZ91 alloys during friction stir welding.