中间层锌箔对铝-钛异种接头微观组织和力学性能的影响

本文旨在通过改善焊接工艺,提高铝-钛接头性能,扩大铝-钛复合件的应用范围.通过在铝-钛熔钎焊接工艺中添加锌箔,探讨了中间层锌箔对铝-钛接头微观组织和力学性能的影响.采用TIG焊机对铝/钛异种金属板材进行熔钎焊接实验,利用金相显微镜、扫描电镜、能谱仪、维氏硬度计和电子拉伸机对铝/钛接头的微观组织和机械性能进行分析.研究发...     

Laser arc hybrid weld microstructure in nickel based IN738 superalloy

Abstract

A study of the microstructural characteristics of laser arc hybrid welded nickel based IN738 superalloy was performed. Laser arc hybrid welding produced a desirable weld profile in the alloy, similar to what is usually obtained during laser beam welding, and no cracking occurred exclusively in the fusion zone. Elemental partitioning pattern in the fusion zone was studied by electron probe microanalysis and calculating the volume fraction of the weld metal that resulted from the consumption of the filler wire. The result showed that Ti, Ta, Nb, Mo, Al and Zr partitioned into the interdendritic regions of the fusion zone. SEM and TEM examination of the fusion zone showed the presence of secondary solidification reaction constituents, which consists of MC type carbides. The study further revealed that non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the heat affected zone (HAZ), which consequently resulted in extensive HAZ intergranular cracking during welding. Although laser arc hybrid welding appears promising for improving the weldability of nickel based IN738 superalloy, a suitable weldability improvement procedure is required in order to minimise HAZ intergranular cracking and thereby enhance the applicability of this technology to the joining of the superalloy.     

Microstructural characteristics and mechanical properties in laser beam welds of Ti6Al4V alloy

The microstructural characteristics and mechanical properties in laser beam welds of Ti6Al4V alloy were investigated. The microstructural characteristics in the heat affected zone and fusion zone change obviously after laser beam welding, which are strongly influenced by the welding conditions. The mechanical properties of the welds are evidently dependent on the microstructural characteristics, and the strengthening in the heat affected zone and fusion zone is mainly attributed to the formation of martensite.     

Improving the wear resistance of AA 6061 by laser surface alloying with NiTi

To improve the wear resistance of a popular aluminum alloy AA 6061, a 1.5 mm thick hard surface layer consisting of Ni–Al and Ti–Al intermetallic compounds was synthesized on the alloy by laser surface alloying technique. NiTi powder was preplaced on the aluminum alloy substrate and irradiated with a high-power CW Nd:YAG laser in an argon atmosphere. With optimized processing parameters, a modified surface layer free of cracks and pores was formed by reaction synthesis of Al with Ni and Ti. X-ray diffractometry (XRD) confirmed the main phases in the layer to be TiAl₃ and Ni₃Al. The surface hardness increased from below 100 HV for untreated AA 6061 to more than 350 HV for the laser-treated sample. Accompanying the increase in hardness, the wear resistance of the modified layer reached about 5.5 times that of the substrate.     

Mikrostruktur und mechanische Eigenschaften der reibgeschweißten γ‐TiAl‐Feingusslegierung Ti‐47Al‐3.5(Mn+Cr+Nb)‐0.8(B+Si)

Microstructure and mechanical properties of friction welded γ‐TiAl based alloy Ti‐47Al‐3.5(Mn+Cr+Nb)‐0.8(B+Si) in investment cast condition. This paper describes properties of joints produced by friction welding of the intermetallic γ‐TiAl based alloy Ti‐47Al‐3.5(Mn+Cr+Nb)‐0.8(B+Si) in investment cast and hot‐isostatically pressed condition. The effect of friction welding parameters on microstructure and local properties are examined and discussed. It is found that the properties of the joint are essentially affected by properties of as‐cast Ti‐47Al‐3.5(Mn+Cr+Nb)‐0.8(B+Si) base material, both at room temperature and 700 °C.     

Effect of laser-arc hybrid welding on fracture and corrosion behaviour of AA6061-T6 alloy

The welding condition of the hybrid laser-gas metal arc (GMA) welding for AA6061-T6 alloy was optimized by tensile test. Formability performance was checked by the bend test. Fractographic analysis indicates a large number of fine ductile type voids in the fracture surface. The microstructure measurements exhibit a dendritic cellular structure in the weld fusion zone (WFZ) and a partially melted zone adjacent to the fusion boundaries. The corrosion behaviour of the weldment and the base alloy were investigated by weight-loss test in nitric acid solution. The WFZ suffers more severe pitting than the rest regions in the weldment. It shows that corrosion cracking is owing to the precipitation of intermetallic phases and the formation of galvanic corrosion couplings in the weldment of AA6061-T6 alloy.     

Microstructural analysis of fusion and heat affected zones in electron beam welded ALLVAC 718PLUS™ superalloy

The fusion zone and heat affected zone (HAZ) microstructures of electron beam welded superalloy 718PLUS™ (718 Plus) that has been newly developed by ATI ALLVAC were examined. The microsegregation pattern during solidification of the fusion zone indicated that while Fe, Co, W, and Cr segregated to the core of the gamma dendrites, Nb, Ti, and Al were extensively rejected into the interdendritic liquid. Electron diffraction and X-ray microanalysis using transmission electron microscopy (TEM) of the fusion zone showed that the major secondary phases that formed from the interdendritic liquid were gamma/MC type carbide eutectic and gamma/Laves eutectic constituents. HAZ microstructure showed partially melted zone immediately adjacent to the fusion zone and intergranular microfissuring associated with resolidified products which suggested that HAZ cracking in this alloy occurred by liquation cracking. Microstructural examination of the HAZ using analytical scanning electron microscope showed resolidified gamma/Laves eutectic on the cracked and backfilled grain boundaries. Fine resolidified MC type carbide particles were also observed in the HAZ. Causes of grain boundary liquation were identified and the solidification of intergranular liquid in the HAZ was discussed.     

Sintering behavior of mechanically alloyed Ti-48Al-2Nb aluminides

Ti-Al intermetallics have been produced using mechanical alloying technique. A composition of Ti-48Al-2Nb at % powders was mechanically alloyed for various durations of 20, 40, 60, 80 and 100 h. At the early stages of milling, a Ti (Al) solid solution is formed, on further milling the formation of amorphous phase occurs. Traces of TiAl and Ti₃Al were formed with major Ti and Al phases after milling at 40 h and beyond. When further milled, phases of intermetallic compounds like TiAl and Ti₃Al were formed after 80 hours of milling and they also found in 100 h milled powders. The powders milled for different durations were sintered at 785°C in vacuum. The mechanically alloyed powders as well as the sintered compacts were characterized by XRD, FESEM and DTA to determine the phases, crystallite size, microstructures and the influence of sintering over mechanical alloying.     

Investigation of In Situ and Conventional Post‐Weld Heat Treatments on Dual‐Laser‐Beam‐Welded γ‐TiAl‐Based Alloy

This paper describes a way to improve the microstructure and mechanical properties of welding seams by in situ and conventional post‐weld heat treatments for laser beam welding of the Ti–45Al–5Nb–0.2C–0.2B alloy. The seams are crack‐free with reduced longitudinal residual stress and higher elongation to fraction after post‐weld heat treatment. The welding zone consists of α₂ after welding, transforms to a massive γ during in situ post‐weld heat treatment, and finally forms a convoluted microstructure after conventional heating. The phase composition across the welding zone is discussed.     

Comparative Evaluation on the In Vitro Biological Performance of Ti45Al8.5Nb Intermetallic with Ti6Al4V and Ti6Al7Nb Alloys

The corrosion resistance of Ti45Al8.5Nb intermetallic alloy in artificial saliva and its cytocompatibility was studied via electrochemical tests, scanning electron microscopy, ion release measurement, and MTT assay, with contemporary biomedical Ti6Al4V and Ti6Al7Nb alloys as comparison. The results demonstrate that the corrosion potential (E_corr) and the corrosion current density (i_corr) of the three experimental alloy samples are similar and there is no statistically significant difference among them (p > 0.05). The Al³⁺ ion releasing concentration for Ti45Al8.5Nb intermetallic and Ti6Al7Nb alloy after anodic polarization are close. The relative cell proliferation rates of the three experimental alloy extract groups are all over 90% at various cultivation periods (1, 3, and 5 d), and there is no obvious difference for the MG63 cell morphologies comparing with that of the negative group, reaching confluence after 5 d culture and showing well stretched, which indicates that Ti45Al8.5Nb intermetallic alloy has a good cytocompatibility with the Grade 1 RGR value (no toxicity) according to ISO 10993‐5: 1999.     

Nb掺杂对Ti-Al合金化层抗高温氧化性能的影响

为提高钛合金TC4的抗高温氧化性能,采用激光表面合金化技术在钛合金表面制备不同Nb掺杂量的Ti-Al合金化层。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、箱式电阻炉等对合金化层的组织结构和高温氧化行为进行分析测试。结果表明,合金化层主要组成物相为TiAl以及少量的Ti_3Al相。Nb主要以置换溶质原子的形式固溶于合金化层中。合金化层组织均匀,与基体呈典型的冶金结合,在不含Nb的Ti-Al合金化层中发现大量的表层裂纹及少量的贯穿性裂纹,而在Nb掺杂的合金化层中未发现明显的宏观裂纹。合金化层在800℃保温1000h的氧化增重显著低于基体,表现出优异的抗高温氧化性能。相比而言,随着Al含量和Nb掺杂量的提高,合金化层的抗高温氧化能力也随之提高。Nb掺杂提高Ti-Al合金化层抗高温氧化性能的作用机理包括减少TiO_2中的空位缺陷、细化氧化物颗粒及促进Al_2O_3的形成。     

Improving interfacial properties of a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications

Dissimilar welds of aluminium alloy AA6056 and titanium alloy Ti6Al4V were produced by a novel technique. AA6056 sheet was machined at one end to a U-slot shape, enabling the intake of the Ti6Al4V sheet. The Al-alloy U-slot was then butt welded by split laser beam without using a filling wire, thus making a weld by melting only the Al-alloy. Thereby the intermetallic brittle phase TiAl₃ formed at the weld interface and affected mechanical properties. As a continuation of the previous work, the joint design was modified by chamfering Ti6Al4V to reduce the formation of interfacial TiAl₃. It is shown in this work how this seemingly insignificant joint modification has refined microstructure and increased hardness and strength. The most impressive feature was the improved resistance to fatigue crack propagation whereby the fracture type in the fusion zone of AA6056 adjacent to the weld interface changed from partially intercrystalline to completely transcrystalline. Possible metallurgical processes leading to the property improvements are discussed.     

Improved mechanical properties of Ti–6Al–4V alloy by electron beam welding process plus annealing treatments and its microstructural evolution

In this study, we investigated the effect of post weld annealing treatments on the mechanical properties of a Ti–6Al–4V alloy following electron beam welding (EBW). The operational parameters used in this EBW process together with suitable annealing treatments appeared to substantially enhance the tensile properties of the Ti–6Al–4V weldment, suggesting that EBW is a promising method for industrial application. Moreover, we report for the first time that γ-TiAl + α₂-Ti₃Al formed in the fusion zone of the Ti–6Al–4V EBW weldment and exhibited the same lamellar structure, orientation relationship, deformation mechanism, and slip system as common Ti–Al-based alloys do. The presence of these intermetallic compounds affected the mechanical properties of the weldment. We discuss the related phase transformation, microstructural evolution, and characteristics of the precipitates formed.     

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

Investigations were continued on the dissimilar laser beam welds of AA6056 and Ti6Al4V, fabricated by inserting Ti‐sheet into the profiled Al‐sheet and melting AA6056 alone. By using microstructure, hardness and strength as the criteria, sites exhibiting non‐uniform microstructure and localized plastic deformation due to strength mismatch were investigated in two orientations: ? crack parallel to the weld and ? crack perpendicular to the weld for fatigue crack propagation and fracture toughness at room temperature. Effect of temper of AA6056 on these properties was studied for two conditions; welding in T4 followed by post weld heat treatment T6, and welding in T6 and naturally aged for a defined period. The orientation “crack parallel to the weld” was investigated in 3 locations on the side of AA6056: the interface and the two changeovers on the Al‐side. Firstly, between the fusion zone and the heat affected zone (3 mm from the interface) and secondly, between (primary) heat affected zone and towards the base material (7 mm from the interface). Although brittle intermetallic TiAl₃ had been formed at the interface, uncontrolled separation or debonding at the interface was not observed. Insofar the bond quality of the weld was good. However, the ranking of interface was the lowest since fatigue crack propagation was relatively faster than that in the fusion zone and heat affected zone, and fracture toughness was low. Therefore, unstable fatigue crack propagation is observed when the crack propagates perpendicular to the weld from AA6056 towards Ti6Al4V. The results have shown that the dissimilar joints exhibit improved performance when laser beam welded in the T6 condition.     

Gap-free fibre laser welding of Zn-coated steel on Al alloy for light-weight automotive applications

As a result of new policies related to global warming announced by the European Union, avoiding unnecessary energy waste and reducing environmental pollution levels are becoming a major issue in the automotive industry. Accordingly, the lap welding of Zn-coated steels process, which is commonly used for producing car doors, has been gradually developed to lap welding of Zn-coated steel to light materials, such as Al alloy, Mg alloy and composite materials, in order to effectively reduce the vehicle weight. In certain part of car manufacture, organic glues are used to temporally join the Zn-coated steels and Al alloys before permanent welding takes place. The stability of such temporary joining by glues needs improving. Laser “stitching” or low strength welding could be considered as an alternative. However, challenges exist in joining Zn-coated steel on Al alloy by laser welding, due to significant differences of material properties between the two welding materials. Porosity, spatter and intermetallic brittle phases are readily produced in the weld. In this study, the effects of welding speed, laser power, number of the welding passes and type of shielding gas in gap-free welding of Zn-coated steel on Al alloy were investigated using a 1 kW single mode continuous wave fibre laser. Results show that a weld with higher shear strengths in the laser stitching application and less intermetallic phases could be obtained when nitrogen gas was used as the shielding gas. The corrosion resistance and the surface finish of the weld could be improved in double pass welding, especially when argon gas was used as the shielding gas.     

钛/铝异种合金脉冲激光焊接接头裂纹产生机理

目的 对0.8 mm厚的Ti6Al4V钛合金和2 mm厚的AA6060铝合金薄板进行脉冲激光焊接,分析异种轻合金激光焊接裂纹产生的机理及界面结合机理。方法 采用扫描电镜、EDS能谱以及显微硬度计等微观表征分析方法,对焊接接头的形貌特征、成分以及显微硬度进行分析,探索焊接接头处裂纹产生的原因。结果 钛/铝脉冲激光焊接性较差,接头存在严重的裂纹缺陷,裂纹多集中在焊缝与铝母材交界处以及焊缝中心区域位置,主要以热裂纹为主;接头焊缝可能存在大量的Ti-Al金属间化合物以及少量未熔的钛,其界面层主要成分推测为层状TiAl和外层锯齿状的TiAl3;接头整个焊缝区域的平均显微硬度为HV0.1420,其硬度水平远远高于焊缝两侧铝合金母材,也高出钛合金母材很多。结论 钛铝金属间化合物使钛铝焊接接头焊缝区脆性增大,另外接头焊缝区存在较大的组织应力、热应力、拉压应力、拘束应力等复杂应力,致使焊缝内存在较严重的裂纹缺陷。     

Microstructure characteristics of thick aluminum alloy plate joints welded by fiber laser

It's difficult to weld high strength thick plate since the groove is huge when using traditional arc welding, and the weld tends to be softened and large deformation could occur after multi-layer welding. All of these can affect the industrial application of high strength thick plate wielding. In this case, developing advanced welding technology and welding material is necessary to optimize the microstructure and performance of the welds. Fiber laser has many advantages such as good monochrome and high quality laser beam. In order to decrease the heat damage to the base metal from the welding heat source, low heat input is employed for welding thick plate. Fiber laser is applied in the welding of 20 mm thick Al–Zn–Mg–Cu alloy with super narrow gap filler wire. The microstructure comparison of Al–Mg–Mn alloy and Al–Mg–Mn–Zr–Er alloy welded joints reveals that a huge amount of fine equiaxed grains is formed in the weld zone of Zr and Er micro-alloying Al–Mg–Mn alloy welding wire and a great number of precipitation strengthening phases are precipitated in the weld zone after the heat treatment of welded joints in the entirety.     

The influence of adhesive on the Al alloy in laser weld bonding Mg–Al process

Laser weld bonding is a new welding technology, being used to join Mg–Al alloys. The penetration depth of LWB Mg–Al joint was larger than that in simply laser welding joint in same welding parameters. The temperature at the edge of the Al fusion zone in LWB Mg–Al joint was higher than that in laser welding joint, which was measured through the thermal couples. The laser-introduced plasma in LWB Mg–Al process is observed by the high-speed camera, which is different from that in laser welding process. The surface temperature and state of the Al alloy were changed because of the addition of the adhesive, thus the laser absorptive of Al alloy was increased in LWB process, comparing with that in laser welding process; and the decomposition of the adhesive would make a depression in the Al fusion zone, which would be beneficial to the formation of keyhole welding in LWB Mg–Al joint.     

Microstructural evolution in AZ91D magnesium alloy during electron beam welding

Vacuum electron beam welding can have a low heat input, which means there is a minimum heat affected zone during welding of AZ91D magnesium alloy. From the observed microstructure, the weld of the AZ91D magnesium alloy can be divided into four regions, which are the weld metal zone, a partially-melted zone adjacent to the fusion boundary, a partially-melted zone adjacent to the base metal and the base metal zone. A sharp transition from the fusion zone to the non-melted zone, especially the characteristic partial melting microstructure and nature of the alloy elements, was observed. It was found that significant partial melting had taken place in the very narrow region around the weld metal of the AZ91D magnesium alloy. The Al content of eutectic β-Mg₁₇Al₁₂ in the partially-melted zone adjacent to the fusion boundary was close to the content in the continuously precipitated eutectic β particles in the fusion zone and much lower than the eutectic β in the base metal. The fully melted eutectic β-phase coexisted with the partially melted eutectic β phase in the partially-melted zone adjacent to the base metal.     

水下搅拌摩擦焊对铝/铜接头组织与性能的影响

目的 采用搅拌摩擦焊,对比分析大气环境和水下环境下铝/铜接头的组织与性能,以期获得力学性能更优异的铝/铜焊接接头。方法 利用搅拌摩擦焊,在焊接速度为40 mm/min、旋转速度为1 000 r/min的条件下,分别在大气环境和水下环境下对厚度为9 mm的6061铝合金板和T2纯铜板进行焊接。然后,对铝/铜界面、焊核区进行扫描电镜及能谱分析,并对铝/铜界面及焊核区进行物相分析,确定产物相组成。最后,对铝/铜试样进行拉伸及硬度检测。结果 铝/铜接头均无裂纹、气孔等缺陷。铜颗粒弥散分布在焊核区,铝/铜界面形成金属间化合物层。水下搅拌摩擦焊下界面元素扩散距离明显变短,且金属间化合物厚度更薄。铝/铜接头的金属间化合物为AlCu和Al4Cu9。大气环境焊接下接头的抗拉强度为130.6 MPa,断裂方式为脆性断裂;水下焊接下接头的抗拉强度为199.5 MPa,断裂方式为韧性断裂。水下环境下的接头硬度值更高,其中热影响区的硬度最低值约为65HV。结论 水下搅拌摩擦焊铝/铜接头无裂纹、气孔等缺陷。组织上,水下搅拌摩擦焊的铝/铜接头界面元素扩散距离更短,硬脆的金属间化合物更少;性能上,水下搅拌摩擦焊的铝/铜接头强度更高,抗拉强度达到199.5 MPa,达到母材的74.4%。