厚板Ti6Al4V合金低真空激光焊接接头组织及力学性能

采用低真空激光焊接技术对40 mm厚Ti6Al4V合金进行焊接,对比分析不同位置的微区组织与力学性能. 结果表明,母材由等轴初生α相和β转变组织组成,热影响区组织为α相、残余β相和急冷准稳态的α'马氏体,焊缝熔凝区组织主要包括不同尺寸及分布状态的α'马氏体以及慢冷却速率下形成的α相. 焊接接头抗拉强度平均值为988 MPa,断裂位置均位于母材. 焊缝上部和中部焊缝区的平均冲击吸收能量为28.8 J,明显优于下部24.8 J. 焊缝熔凝区底部区域存在细长状、密集程度较高的α'马氏体会劣化材料冲击韧性. 相比之下熔凝区中、上部形成的短粗状、密集程度较低的α'马氏体组织的冲击韧性较高, 为Ti6Al4V合金板材的连接及进一步提高接头的力学性能提供了数据支撑及相关理论依据.     

Homogenisation of chemical composition and microstructure in laser filler wire welding of AA 6009 aluminium alloy by in situ electric current stirring

Owing to the rapid cooling rates, the deposited and base metals could be mixed incompletely during laser welding of Al alloys in most cases. The objective of this research is to explore a possible method to promote the mixing of materials inside the molten pool by making use of the magnetofluid dynamic effect of electric current. Full penetration CO₂ laser welding of 3?mm thick alloy 6009 sheets was performed with an external electric current simultaneously into the weld pool via a filler wire. It is found that the deposited metal is mainly concentrated on the upper part of the weld fusion zone, and the weld zone microstructure is non-uniform without the electric current addition. With the application of an electric current, the weld fusion zone geometry is reshaped, and the chemical composition and microstructure of the weld metal are homogenised. The mechanism is found to be electromagnetic force stirring of the molten pool.     

Porosity and microstructure in pulsed Nd:YAG laser welded Ti6Al4V sheet

The overlapping factor of pulsed laser welding is used to help understand the correlation between welding parameters and the quality of Ti6Al4V welded joints. The number of porosity decreases with the increase in overlapping factor, and the welded joints are almost completely free of porosity when overlapping factor is greater than 75%. This can be attributed to the fact that the remelted volume of the spot region increases with the increase of overlapping factor, which assists porosity formed in the previous pulse wave in escaping from molten pool formed by the subsequent pulse. With the increase of overlapping factor, the weld microstructure becomes much coarser and the width of the fully transformed region of heat affected zone increases, which reduces the microstructure gradient and microhardness gradient from the fusion zone to heat affected zone. A method to evaluate the porosity susceptibility of a specific welding condition prior to actual welding process is presented.     

A study on keyhole evolution and weld ripple formation in dissimilar welding under pulsed laser

A three-transient multiphase model is developed to study the dissimilar metal welding of pure niobium plate to titanium alloy Ti–6Al–4V sheet under pulsed laser. The physical process of dissimilar metal welding involves melting, resolidification, mass transfer, self-consistent keyhole, and weld bead formation. The major physical factors, such as recoil pressure induced by vapourisation, surface tension, heat transfer, fluid flow, Marangoni shear stress, buoyancy force, and their coupling are considered. The results show that the keyhole mainly occurs on the Ti–6Al–4V side due to the differences in physical properties of the materials. The effects of pulse overlapping factor on the weld bead are studied. It is found that the pulsed laser has a significant influence on the weld bead formation. The mixing of materials mostly occurred in the upper part of the molten pool. The simulated weld bead profile and the phase distribution agree well with the experimental results.     

原位生成铝基复合材料的激光焊接

采用大功率激光器研究新型铝基复合材料TiB2/ZL101的焊接性能,TiB2粒子的存在增加了焊缝熔池粘度降低了熔池流动性,影响了焊缝成形,增加了气孔敏感性.焊缝中气孔主要来源于氢和复合材料中的残留盐.激光焊接过程中较大的冷却速度使得焊缝晶粒非常细小,TiB2粒子在焊缝中分布更均匀,没有出现粒子偏析,主要是因为TiB2粒子是属于纳米级,在凝固过程中被凝固界面前沿所捕获而没有被推移.TiB2粒子没有与铝基体发生界面反应生成脆性相Al3Ti及AlB2,TiB2粒子与Al基体界面结合较好.结果表明,激光焊接后没有破坏TiB2粒子的增强效果.     

热输入对双光束激光焊接Ti-6Al-4V合金T型接头焊接过程、焊缝成形、组织及力学性能的影响

采用双光束同步激光填丝焊接的方法制备了Ti-6Al-4V合金T型接头,使用高速摄像机拍摄了焊接过程图像并研究了热输入对焊接过程稳定性、焊缝成形、组织及力学性能的影响。试验结果表明,热输入显著影响熔池行为和填丝焊接熔滴过渡,进而影响T型接头焊缝形貌及质量。随着热输入的增加,T型接头组织发生变化,晶粒尺寸变大。热影响区及焊缝处的马氏体使得这2个区域的显微硬度高于母材。另外,沿蒙皮方向及筋条方向的抗拉伸强度随着热输入的增加而增大。由于接头处马氏体增强作用,拉伸断裂均发生于母材处。     

Mechanisms of joining aluminium A6061-T6 and titanium Ti–6Al–4V alloys by cold metal transfer technology

Abstract

Cold metal transfer (CMT) welding–brazing joining of Ti6Al4V and Al A6061-T6 was carried out using AlSi₅ wire. The joining mechanisms and mechanical properties of the joints were identified and characterised by scanning electron microscope, energy dispersive spectroscopy and tensile–shear tests. Desired CMT joints with satisfied weld appearances and mechanical properties were achieved by overlapping Ti on the top of Al. The joints had dual characteristics of a welding joint on the aluminium side and a brazing joint on the titanium side. Three brazing interfaces were formed for the joint, which increased the strength of the joint. An intermetallic compound layer was formed at the brazing interface, which included Ti₃Al, TiAl and TiAl₃. Two different fracture modes were also observed: one fractured at the welding/brazing interface and weld metal and the other at the Al heat affected zone (HAZ). Clearly, the joints fractured at the Al HAZ had higher tensile strength than those fractured at the welding/brazing interface and weld metal.     

Relationships between microhardness,microstructure, and grain orientation in laser-welded joints with different welding speeds for Ti6Al4V titanium alloy

The microhardness curve trend and its relationships with microstructure and misorientation were analyzed to enhance the comprehension of the microstructure and mechanical property of micro-areas in Ti6Al4V laser-welded joints with different welding speeds. The microhardness measured on the fusion line (H_m) is the highest from the weld center to the base metal. H_m increases with increasing weld width in a welded joint and increasing degree of the non-uniformity in all studied welded joints. The microhardness decreases from the weld metal to the base metal with decreasing amount of martensite α’ and increasing amount of original α phase. When the microstructure is mainly composed of martensite α’, the microhardness changes with the cooling rate, grain size of the martensite, and peak values of the fraction of misorientation angle of the martensite in a wide weld metal zone or weld center at different welding speeds, whereas the difference is small in a narrow weld metal zone.     

Joint strength and behaviour of coated aluminium in laser lap welding of steel sheets

When galvanized steel sheets are closely overlapped and welded by laser lap welding, a large amount of molten metal spatters, resulting in a poor surface appearance of the weld and weakened strength of the welded joint, as compared with that of cold-rolled steel sheets. Whereas in the case of aluminium-coated steel sheets, even when they are closely overlapped and welded by laser lap welding, no spattering occurs. Thus, a good surface appearance of the weld is obtained, but the welded joint has lower strength. In both the mentioned cases, it is known that if a clearance of about 0.1 mm is provided between the steel sheets, laser lap welding produces a good surface appearance of the weld and the welded joint strength equal to that of the cold-rolled steel sheets. This report discusses specifically how, in laser lap welding of overlapped Al-coated steel sheets, Al of the coated layer comes to enter the weld metal, also specifically how to reduce the joint strength, as well as what behaviours of Al are present when a clearance is provided between the steel sheets. When the steel sheets are closely overlapped and welded, Al becoming molten on the base metal side of the bond of the overlapped face becomes swallowed up by the bath streams of the molten pool, flowing into the molten pool, then forming the Fe–Al intermetallic compound, while not being sufficiently stirred. It is considered that when subjected to the tensile shear test, the Fe–Al intermetallic compound starts to fracture, thereby causing a partial loss of the weld metal and a reduction in the joint strength. On the other hand, when a clearance is provided between the steel sheets, it may be inferred that the fusion Al on the base metal side of the bond stays in place without flowing into the molten pool, consequently not forming the Fe–Al intermetallic compounds within the weld metal.     

Microstructures and mechanical properties of Ti–Al–V–Nb alloys with cluster formula manufactured by laser additive manufacturing

Ti–Al–V–Nb alloys with the cluster formula, 12[Al–Ti₁₂](AlTi₂)+5[Al–Ti₁₄](V,Nb)₂Ti, were designed by replacing V with Nb based on the Ti–6Al–4V alloy. Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.% were prepared by laser additive manufacturing to examine their formability, microstructure, and mechanical properties. For single-track cladding layers, the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability. The alloy, Ti–5.96Al–1.94V– 3.54Nb (wt.%), exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder. The microstructures of the bulk samples contained similar columnar β-phase grains, regardless of Nb content. These grains grew epitaxially from the Ti substrate along the deposition direction, with basket-weave α-phase laths within the columnar grains. The α-phase size increased with increasing Nb contents, but its uniformity decreased. Along the deposition direction, the Vickers hardness increased from the substrate to the surface. The Ti–5.96Al–1.94V–3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between the α-phase size and its content among the designed alloys.     

Numerical simulation of molten pool dynamics in high power disk laser welding

A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed.     

液相分离对T2紫铜/316L不锈钢接头组织及性能的影响

采用钨极氩弧焊填充纯铜焊丝进行T2紫铜/316L不锈钢异种金属焊接工艺试验,分析了接头微观组织的形成机制. 结果表明,使用纯铜焊丝时,铁-铜液相分离对铜/钢焊缝组织的形成起主导作用. 以铜为基体的焊缝中分布着大量由铁-铜初次液相分离形成的富铁球,在其内部还分布有标志着铁-铜二次液相分离的富铜相. 富铁球内的析出相在表面能梯度和密度差的作用下,向富铁球中心呈球状聚集. 由于成分和所处区域的冷却速率不同,富铁球呈现不同的形貌. 基于熔池边界凝固理论,分析了接头铜/钢界面未混溶区宏观偏析机制. 填丝焊时,熔池边缘形成非等温边界. 纯铜焊丝制备接头铜/钢界面处液态钢母材的温度高于熔池主体,导致岛状和半未混溶区的形成. 接头的铜侧存在由粗大晶粒和正常尺寸晶粒组成的软化区,拉伸试样均断裂于此,抗拉强度达到铜母材的81.7%.     

基于Ti中间层的SiCp/6061-T6Al MMCs低功率激光-TIG复合焊组织与性能

以0.1mm厚的Ti箔做中间夹层,使用低功率激光-TIG复合焊的方式对SiCp/6061-T6Al MMCs 进行焊接,并对接头的宏观形貌、显微组织、物相、电阻率、抗拉强度及断口形貌进行分析。结果表明：激光功率对焊缝的成形有着较大影响;Ti箔的加入基本抑制了焊缝中针状Al₄C₃生成,并生成TiC增强相以及条状TiAl₃;焊缝区为等轴晶组织,熔合区为柱状晶组织,热影响区组织变化不明显;随着激光功率的增加接头的电阻率呈现出增加的趋势,并明显高于母材;在554W时接头的抗拉强度可达196.98MPa,是母材强度的54.71%。接头断口中几乎没有气孔,韧窝中的第二相粒子以TiC为主,接头呈现出以脆性断裂为主的脆-韧性混合断裂特征。     

镀Cu层调控AZ31B/TC4激光熔钎焊接特性

采用钛表面电镀铜作为中间层,开展镁(AZ31B)/钛(TC4)对接激光填丝熔钎焊,对镁/钛非互溶不反应焊接体系进行调控. 主要研究了激光功率对镁/钛接头焊接质量的影响规律,进一步分析了不同工艺参数条件下镁/钛界面组织及接头力学性能. 结果表明,铜镀层提高了熔融焊丝在母材表面的润湿铺展并卷入到焊缝组织中,随着激光功率的增加,镁/钛界面形成Ti₃Al反应层的能力提高,界面结合强度随之提高. 在较高激光功率1 700 W时,接头拉伸载荷最高达到3 085 N,为镁母材的76.2%,而接头在较高激光功率下的断裂模式也由完全界面断裂转变为部分界面断裂.     

SiCp/Al复合材料电子束焊接接头组织及性能

对SiCp/Al复合材料自身进行电子束焊接,研究了其接头成形、焊缝组织、热影响区组织及接头力学性能.结果表明,SiCp/Al复合材料自身直接电子束焊接时,接头的主要缺陷是焊缝成形差、易形成两侧堆积颗粒物的凹槽;焊缝组织中存在界面反应产生的灰白色初生硅、深灰色针状相Al4C3以及Al-Si共晶中的浅灰色针状共晶硅,形成脆性区,拉伸断裂位置便在此处,断裂为脆性断裂.熔合区附近硬度较高,与焊缝区组织及硬度差异较大.接头的最高强度为73 MPa,仅占母材平均抗拉强度的41％.     

Ti对SiCp/6092铝基复合材料激光焊焊缝组织和性能的影响

采用不同厚度的Ti箔作为填充材料对SiC_p/6092铝基复合材料进行激光焊接,分析不同含量Ti元素对焊缝组织和焊接接头力学性能的影响. 结果表明,Ti箔的加入可以有效改善熔池流动性,从而减少焊缝区的工艺型气孔. 同时,填加Ti箔可以避免激光直接照射在母材上引起的低熔点元素烧损. 在激光的照射下,Ti箔完全熔化并与在热传导作用下部分熔化的母材金属发生冶金反应,Ti元素含量过少时,界面反应得不到有效抑制,焊缝中仍分布有大量的脆性相,Ti元素对焊接接头的力学性能改善不明显;Ti元素含量过多时,Ti元素在熔池中未能扩散开,富余的Ti元素与Al元素反应生成Al₃Ti. 过分长大的Al₃Ti呈片状,将对接头的力学性能不利. 因此,向熔池中加入适量Ti元素有利于改善熔池冶金反应,从而提升接头力学性能,焊接接头的最大抗拉强度可达206 MPa.     

铝/钛异种金属旁路分流MIG电弧熔钎焊特性

以1 mm厚6061铝合金与TC4钛合金板为试验材料,进行旁路分流MIG电弧熔钎焊工艺试验,得到均匀美观的焊缝成形.分别采用金相显微镜、扫描电镜、万能拉伸试验机进行研究.结果表明,界面层上方金属间化合物以柱状晶形式存在,呈现短而密集的状态.界面层靠近钛侧易形成AlTi,而界面层靠近铝侧易形成Al₃Ti,TiSi₂等金属间化合物,由于焊接过程中熔池内部温度的变化不均,会使界面层中出现Al₁₁Ti₅过渡相.拉伸试验表明,接头最高抗剪强度达182.6 MPa,约为铝母材的97.6%,断裂发生在铝母材热影响区,断口出现一定量的颈缩.     

Dissimilar Ti/Mg alloy butt welding by fibre laser with Mg filler wire – preliminary study

Abstract

A fibre laser was used to join Ti–6Al–4V alloy to AZ31B Mg alloy with the same thickness of 2 mm, and a filler wire was used to avoid weld underfill resulting from Mg vaporisation. The acceptable joints were only obtained when the laser beam was offset from the edge of the weld seam at 0·2 mm to the AZ31B side of the joint. Cross-weld tensile testing found joint strengths of up to 200·3 MPa, which is 85·1% of the AZ31B tensile strength. All the joints were fractured at the Ti/fusion zone interfacial layer. When the laser offset increased from 0·2 to 0·3 mm or laser power reduced to 1·2 kW, the joining mode of the interfacial layer changed from a semimetallurgical joining with high strength to a mechanical joining with poor strength. Moreover, the fracture surface of acceptable joints was characterised by scraggly remaining weld metal, while that of poor joints was almost only characterised by smooth Ti surface.     

铝/钛异种金属激光/激光-CMT复合熔钎焊工艺及其组织与力学性能

选用5A06铝合金和Ti6Al4V钛合金为母材,ER4047焊丝和粉状Nocolok钎剂为填充材料,采用激光熔钎焊和激光-CMT复合熔钎焊两种焊接方法,并对两种焊接接头的微观组织和力学性能进行对比分析.结果表明,激光熔钎焊与激光-CMT复合熔钎焊在合适的焊接工艺下均容易获得连续、稳定的焊接接头.铝/钛激光熔钎焊和激光-CMT复合熔钎焊焊缝中部组织均为α-Al固溶体和Al-Si共晶组织.激光熔钎焊和激光-CMT复合熔钎焊均在钛合金上表面处界面反应层最厚,其厚度分别小于10和6μm.激光熔钎焊焊缝偏钛侧界面主要为锯齿状,激光-CMT复合熔钎焊焊缝偏钛侧界面主要为层片状.激光熔钎焊和激光-CMT复合熔钎焊焊接接头均断裂在焊缝区,焊接接头平均抗拉强度分别为252和209 MPa,激光熔钎焊比激光-CMT复合熔钎焊接头抗拉强度高20%,而激光-CMT复合熔钎焊比激光熔钎焊焊接效率提升约1.5倍.     

Effect of welding processes on joint characteristics of Ti–6Al–4V alloy

Abstract

Although Ti–6Al–4V alloys show reasonable weldability characteristics, the joint properties are greatly influenced by the welding processes. Microstructures and tensile and impact properties of welded Ti–6Al–4V alloy were evaluated for high vacuum electron beam welding, CO₂ laser beam welding and gas tungsten arc welding. The resultant tensile and impact properties of the welded joints are correlated with the weld metal microstructure and hardness. The results indicate that the electron beam welding is more suitable for Ti–6Al–4V sheet welding and the welding seam without defects can be obtained. The full penetration butt welds are obtained by gas tungsten arc welding process, but they have many drawbacks such as wide weld seam, big deformation and coarse grains. Laser beam welding has many advantages such as the narrowest weld seam, the least deformation and the finest grains, but it should be studied again for the reasons of unstable welding technologies and strict condition.