Comparative investigation of tungsten inert gas and friction stir welding characteristics of Al–Mg–Sc alloy plates

Al–Mg–Sc alloy plates were welded by FSW and TIG welding. The effect of welding processes on mechanical properties of Al–Mg–Sc welded joints was analyzed based on optical microscopy, transmission electron microscopy, tensile testing and Vickers microhardness measurements. The results show that the mechanical properties of FSW welded joint are much better than those of TIG welded joint; the strength coefficient of FSW joint is up to 94%. Moreover, tensile strength and yield strength of FSW joint are 19% and 31% higher than those of TIG joint, respectively, which are attributed to the preservation of cold working microstructures in the process of FSW. Due to the low welding temperature during FSW process and the excellent thermal stability of Al₃(Sc, Zr) particles, the cold working microstructures can be well preserved. In addition, the FSW joint have asymmetric microstructures and mechanical properties, which are not observed in TIG welded joint.     

Microstructure effects in braze joints formed between Ag/W electrical contacts and Sn-coated Cu using Cu–Ag–P filler metal

Braze joints have been formed between Ag/W electrical contact tips and Sn-coated Cu straps using a Cu–Ag–P-based filler metal by short-cycle direct conductive heating from the Cu strap side. The microstructures of the braze joints have been investigated using a combination of scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, focused ion beam milling, and transmission electron microscopy. The braze joints exhibit regions with two distinct types of microstructures. Type I microstructures contain three micro-constituents: FCC (Ag), FCC (Cu), and a ternary eutectic [(Ag) + (Cu) + Cu₃P]. The difference between the proportions of these phases and those in the baseline filler metal can be accounted for on the basis of P loss due to self-fluxing during the brazing process. Type II microstructures contain mostly (Ag) and (Cu) with a small amount of Cu₃P but no ternary eutectic mixture. Other differences from the Type I regions include a lower P content, incomplete dispersion of the Sn layer, and a refined grain size in the majority (Cu) phase. These effects are accounted for on the basis of local differences in interfacial pressure due to the geometry of the Ag/W contact surface.     

Influence of isothermal solidification on microstructural development in Ni–Si–B filler metals

Abstract

An examination is reported of the microstructure of joints between nickel substrates fabricated using Ni–Si–B filler metal (AWS classification BNi-3). This investigation was undertaken because the presence of residual boride and silicide phases after joining can affect the subsequent mechanical properties of the joint. The microstructures developed in the joints are compared with those formed in similarly heat treated filler metal. Various models of the transient liquid phase process are also considered and predicted times to complete isothermal solidification are compared with experimental values. An initial examination of the influence on filler metal microstructure of a ternary addition (chromium) to the substrate is included.

MST/1506     

Effect of 0.5 wt.% hydrogen addition on microstructural evolution of Ti–6Al–4V alloy in the friction stir welding and post-weld dehydrogenation process

The α + β titanium alloy, Ti–6Al–4V, was thermohydrogen processed with 0.5 wt.% hydrogen and friction stir welded using a W–Re pin tool. Defect-free joints were obtained with proper parameters. Hydrogen was removed from the joint through a post-weld dehydrogenation process. The microstructures of the as-welded and dehydrogenated joints were examined. The effect of 0.5 wt.% hydrogen addition on microstructural evolution of Ti–6Al–4V alloy in the friction stir welding and post-weld dehydrogenation process was revealed.     

搅拌摩擦与氩弧焊铝合金接头疲劳性能的比较

建立了铝合金焊接接头的S-N曲线,对比分析了搅拌摩擦和氩弧焊两种工艺对其焊接接头疲劳性能的影响,结果表明:在载荷相同的条件下,铝合金搅拌磨擦焊接接头的疲劳性能优于氩弧焊接头,搅拌摩擦焊接头的疲劳寿命N=106次的疲劳强度为59-65 MPa,搅拌摩擦焊接接头具有比氩弧焊接头更为细小的晶粒和狭窄的焊接热影响区,阻碍了滑移带的形成和裂纹的扩展,从而提高了接头的疲劳性能,铝合金焊接接头的缺陷是主要的疲劳裂纹源.     

2024铝合金搅拌摩擦焊接头塑性变形行为研究

为了研究搅拌摩擦焊卷焊管坯的力学性能及接头塑性变形行为,以5 mm厚的2024退火态铝合金搅拌摩擦焊板坯为对象,采用网格法测试接头塑性变形分布,用EBSD测量接头各区域晶粒尺寸及位相,并结合SEM观察接头第二相的分布,研究了接头力学性能、应变分布与微观组织之间的关系.研究表明:搅拌摩擦接头强度与母材等强,延伸率下降44%;接头前进侧距离焊缝中心8～17 mm的母材较早出现了应变的集中,局部应变可达23%,而焊核区和接头返回侧母材发生的变形较小,平均应变分别为3%和11%,各区域应变的不均匀主要是由于接头各区晶粒尺寸及位相的差异造成的,导致接头整体延伸率的下降.     

Ultrasonic vibration assisted tungsten inert gas welding of dissimilar magnesium alloys

The effects of ultrasonic vibration assisted (UVA) treatment on the microstructures and mechanical properties of MB3/AZ31 dissimilar magnesium (Mg) alloy joints were studied by microstructural characterization, micro-hardness testing and tensile testing. Results indicate that the welding pores are eliminated and coarse ??-Mg grains of fusion zone are refined to 26 ??m, owing to the acoustic streaming effect and cavitation effect induced by the UVA treatment with an optimal ultrasonic power of 1.0 kW. In addition, Mg₁₇Al₁₂ precipitation phases are fine and uniformly distributed in the whole fusion zone of weldment. Micro-hardness of fusion zone of the Mg alloy joints increases to 53.5 HV after UVA process, and the maximum tensile strength with optimized UVA treatment increases to 263 MPa, which leads to fracture occurrence in the Mg alloy base plate. Eventually, it is experimentally demonstrated that robust MB3/AZ31 Mg alloy joints can be obtained by UVA process.     

焊后热处理对奥氏体／珠光体钢接头熔合区断裂形态的影响

利用扫描电镜对比观察了不同碳含量母材的奥氏体（Ａ）／珠光体（Ｐ）异种钢焊接接头熔使区在焊态和焊后热处理后的断口形态与对应的金相组织。发现焊态接头熔合区的断裂形态由滑移变形、浅纫窝和准解理小面组成，崦焊后的热处理接头熔合区的断裂形态为碳化物带＋放射状解理混合花样。在溶合区两侧可看到明显的边界线和脆－韧转变特征，初步讨论了熔合区粘口的形成机理和焊后热处理对它的影响。     

随机振动载荷下塑封球栅阵列含铅焊点疲劳寿命模型

对塑封球栅阵列(PBGA)封装器件Sn37Pb焊点进行了正弦振动、随机振动实验,得到各个载荷下焊点的疲劳寿命结果.建立了三维有限元模型,进行与实验条件一致的有限元分析,计算焊点的应力;将实验结果与有限元计算相结合,并基于Steinberg寿命预测模型,发展了随机振动载荷下焊点疲劳寿命预测方法.结果表明,疲劳寿命模型预测...     

Fracture mechanics analysis of the effect of substrate flexibility on solder joint reliability

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue life significantly. The reliability of solder joints in real flip chip assembly with both rigid and compliant substrates was evaluated by the accelerated temperature cycling test and thermal mechanical analysis. The mechanism of substrate flexibility on improving solder joint thermal fatigue lifetime was investigated by fracture mechanics methods. Two different methods (crack tip opening displacement, CTOD and virtual crack closure technique, VCCT) are used to determine the crack tip parameters which are considered as the indices of reliability of solder joints, including the strain energy release rate and phase angle for the different crack lengths and temperatures. It was found that the thermal fatigue lifetime of solder joints in flip chip on flex assembly (FCOF) was much longer than that of flip chip on rigid board assembly (FCOB). The flex substrates could dissipate energy that otherwise would be absorbed by solder joints, that is, substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during thermal cycling.     

Microstructure development in resistance spot welded galvannealed IF steel sheet

Abstract

Interstitial free (IF) steels having excellent drawing and forming characteristics find extensive use in autobody panels. Although, resistance spot welded joints are widely used in the automobile industry, little is known about the metallurgical changes which occur during the spot welding process. The investigation of the metallurgical changes is very important for the safety strength of the welded joints. In the present research work, microstructures of the different zones of spot welded interstitial free steels have been characterised by optical, scanning electron and transmission electron microscopes. Microstructural changes at weld and heat affected zone have also been correlated with welding heat input and microhardness values.     

Optimizing the service life of drill-collar joints on the basis of fracture mechanics criteria

A method of calculation of the lifetime of fish-mouth collar joints has been proposed that is based on selecting a model and using the criteria of fracture mechanics. By this method it is possible to optimize the design parameters of collar joints as a function of the cyclic crack resistance of steels. It is shown that the lifetime of a collar joint with a fatigue crack can be predicted, and the size of the crack can be estimated for a certain operating time of the collar joint. The critical values of the length of a fatigue crack were calculated for various types and dimensions of collar joints, which is important in fixing the periodicity of crack detection operations.     

环路热管钎焊制造技术及传热性能数值模拟

为解决环路热管中蒸发器结构连接难的问题,开展了1Cr18Ni9Ti不锈钢与LD10铝合金环路热管封闭结构的大面积软钎焊技术研究,研究了钎料添加方式和焊接温度对接头质量的影响,分析了接头微观组织,并且利用ANSYS有限元软件对蒸发器热传输性能进行了数值模拟,分析了不同程度的缺陷对蒸发器热传输性能的影响.结果表明:焊接温度220℃,采用方式B的焊接接头质量优异,钎着率达到100%,从而设计出一套完整环路热管蒸发器软钎焊的生产工艺流程.     

服役条件下方钴矿基热电元件的界面应力分析

热电器件中, 界面可靠性是影响整体稳定和功率输出的关键因素。对于方钴矿(SKD)器件, 热电臂和电极通过扩散阻挡层(DBL)连接。在高温下, DBL与SKD、电极之间会发生反应并生成复杂的界面结构, 导致界面附近的热、电、力学性能发生变化。本研究根据实际界面结构建立了包含微观结构的有限元模型, 并将其用于分析方钴矿基元件的界面应力状态。采用单层模型对DBL材料参数进行了筛选, 发现热膨胀系数(CTE)和弹性模量(E)对第一主应力有显著影响。采用包含界面微结构的多层模型定量模拟了不同老化温度、时间下元件内部的应力分布, 结果表明在SKD/Zr和SKD/Nb中, CoSb₂反应层最为薄弱, 随着老化时间的延长, 反应层的厚度增加, 界面应力变大。同时, 元件的拉伸试验结果与计算结果吻合较好, 验证了模型的准确性与可行性。本研究为提升SKD/DBL元件的结构稳定性提供了指导, 同时也为精确模拟多层结构中的应力状态提供了研究思路。     

Decrease in fatigue life of Sn - 3.8 wt-%Ag - 1.2 wt-%Cu alloy solder joints due to thermal cycling

Abstract

Copper plates joined with a thin solder layer (60 μm thick) of Sn - 3.8 wt-%Ag - 1.2 wt-% Cu alloy were subjected to heat treatments: a thermal cycling of a temperature range between 321 K and 381 K (Δ T = 60 K) and an isothermal heating at 357 K, and then subjected to a fatigue test at 6 MPa stress amplitude. Solder joints made with a thin solder layer of Sn - Pb eutectic alloy were also examined for comparison. After heat treatments, the η phase developed and dispersed at the bonding interface of the solder joints with increasing numbers of thermal cycling and with increasing time of isothermal heating. Small voids also appeared in the η phase after heat treatments. Fine cracks appeared in the η phase after thermal cycling for 2000 cycles and higher, but no cracks were observed after isothermal heating. There was no large difference in fatigue lifetime after thermal cycling between Sn - Ag - Cu alloy solder joints and Sn - Pb eutectic alloy solder joints. The fatigue lifetime of Sn - Ag - Cu alloy solder joints and Sn - Pb eutectic alloy solder joints was 2 - 3 × 105 with no thermal cycling and was greatly reduced to 0.1 - 0.6 × 10⁵ after 8000 thermal cycles. The fatigue lifetime was also decreased to 0.6 - 1.0 × 10⁵ after isothermal heating for 16 000 min, but the decrease in fatigue lifetime was gradual compared to that after thermal cycling. The decrease in fatigue lifetime after smaller numbers of thermal cycles is explained by coarsening of the η phase, and the large decrease in fatigue lifetime after a large number of thermal cycles is explained by the appearance of cracks in the η phase during thermal cycling.     

GH4145激光点焊工艺及接头性能研究

目的研究不同工艺参数下高温合金的微激光点焊接头性能。方法利用Nd:YAG激光器对厚度为0.23 mm和0.13 mm的GH4145进行搭接点焊,利用微型拉伸机、金相显微镜、硬度计对接头的物理性能进行测试,并观察组织结构。结果脉宽长度为6.0 ms,输出功率百分比为20%(输出功率16 W)时,最大拉伸剪切力为178.59 N,靠近焊点中心位置两边测试点硬度分别达到HV517和HV506。结论接头表面熔化尺寸、焊接接头的拉伸剪切力和硬度随着激光功率的增大而增大,增大到一定值时停止变化,不同参数下达到不同的最大值,组织无明显规律变化。近表面处出现等轴晶,表面以下至熔合线的显微组织为树状晶。通过激光搭接点焊将两片GH4145连接,接头处拉伸剪切力、硬度均低于母材,功率增大有助于提高接头的抗拉强度。     

10Ni5CrMoV钢奥氏体焊缝接头熔合区马氏体带的显微组织

本文研究了A507填充10Ni5CrMoV钢接头熔合区马氏体带的显微组织。"原位取样"TEM分析表明熔合区存在板条马氏体、孪晶马氏体、奥氏体、贝氏体和部分分解的板条马氏体混合组织;彩色金相显示熔合区存在马氏体和奥氏体混合组织;结合Schaeffler图分析结果,可以确定这种混合组织位于OM下熔合区后续熔化滞留层的马氏体带。     

Characterization of microstructure,mechanical properties and corrosion resistance of dissimilar welded joint between 2205 duplex stainless steel and 16MnR

The joint of dissimilar metals between 2205 duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW) and shielded metal arc welding (SMAW) respectively. The microstructures of welded joints are investigated using scanning electron microscope, optical microscope and transmission electron microscopy respectively. The relationship between mechanical properties, corrosion resistance and microstructure of welded joints is evaluated. Results indicate that there are a decarburized layer and an unmixed zone close to the fusion line. It is also indicated that, austenite and acicular ferrite structures distribute uniformly in the weld metal, which is advantageous for better toughness and ductility of joints. Mechanical properties of joints welded by the two kinds of welding technology are satisfied. However, the corrosion resistance of the weldment produced by GTAW is superior to that by SMAW in chloride solution. Based on the present work, it is concluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205 duplex stainless steel and 16MnR.     

Tensile and cyclic deformation response of friction-stir-welded dissimilar aluminum alloy joints: Strain localization effect

Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy examinations to characterize the precipitates required to assess internal stresses.Electron backscatter diffraction was employed to observe the inhomogeneous microstructures of the FSWedjoints.Strain localization appeared in the heat affected zone (HAZ) of AA2024 side.After cyclic deformation of 500 cycles at a total strain amplitude of 0.5 ％,the strength of the dissimilar joints resumed basically to that of AA2024 base material.And the AA2024 HAZ was obviously hardened,which should be attributed to the introduced dislocations during cyclic deformation process.Cyclic hardening capacity of the joints increased with decreasing strain rate.     

690 MPa级低合金高强钢焊接接头组织性能

为探讨690 MPa级低合金高强钢焊接接头组织与性能的关系,采用手工电弧焊(SMAW)和埋弧焊(SAW)获得成形良好的焊接接头,经过拉伸、冲击、弯曲试验及光学显微镜、扫描电镜和透射电镜分析,对两种焊接方法的接头组织性能进行研究.结果表明:两种焊接方法的焊缝组织主要为板条状贝氏体和少量针状铁素体,粗晶区为粗大贝氏体和少量马氏体;焊缝中含有大量分布均匀的微小球形夹杂物;两种焊接方法所得焊接接头都具有较高力学性能,-50℃的冲击断口形貌为韧窝、准解理混合型;埋弧焊焊缝冲击韧性低于手工电弧焊,手工电弧焊熔合线处冲击吸收功小于埋弧焊,但随距熔合线距离增加其值增加更快.显微组织和夹杂物是影响接头性能的主要因素.