Comparison of 2A12 aluminium alloy joint by ultrasonic assisted friction stir welding and friction stir welding

Ultrasonic assisted friction stir welding （UAFSW） is a recent modification of conventional friction stir welding, which adds ultrasonic energy directly into the friction stir welding area by the pin. In this study, 2A12 aluminum alloy was welded by this process and conventional, respectively. The tensile tests, microstructure and fracture surface of FSW joint and UAFSW joint were analyzed. The research results show that the surface forming texture of ultrasonic assisted friction stir welding joint, compared with conventional, is finer and more uniform, showing metallic matte color. The grains are much finer in weld nugget zone, thermo-mechanically affected zone and heat-affected zone; S-phase particles size is much smaller and distribution is more homogeneous in the matrix. The tensile strength of UAFSW joint is 94. 13% of base metal, and the elongation is 11.77%. The tensile strength of FSW joint is 83.15% of base metal, and the elongation is 8.81%. The tests results reveal that ultrasonic vibration can improve the tensile strength and the elongation of welded joints.     

Comparative Analysis on Microstructure and Mechanical Properties between EBW and TANDEM Welding of 7A52 Aluminum Alloy Joint

The plates with 20mm thickness of 7A52 aluminum alloy were welded by electron beam welding and TANDEM welding with ER5356 filler,respectively.The microstructure and mechanical properties of the joints were investigated.The results showed that the microstructure of EBW metal was finer and tighter than TANDEM welding.The heat-affected zone of the EBW joint was narrower,its hardness was higher and the tensile strength improved obviously compared to TANDEM welding.Excellent quality control of the EBW joint was made without abnormal porosity,inclusions and micro-cracks.Therefore,the EBW joint of 7A52 aluminum alloy showed excellent performance.     

Characteristics of Joint Welded by Laser Welding of Aluminium-Lithium Alloy with Filler Wire

The characteristics of weld shape,microstructure,mechanical properties and defects of 5A90 Al-Li alloy joint by laser welding (LBW) and laser welding with filler wire (LWFW) were studied and analyzed.The results indicated that the microstructure of joint by LWFW was fine-grained layer and the equiaxed grain in most of seams,which were similar to the joint by LBW.Compared with the joint by LBW,the microstructure of joint by LWFW tended to fine,and the range of the columnar crystals zone was prone to decrease.The Microhardness of the joint by LWFW (92.57HV0.2) was lower than that by LBW (95.65HV0.2),but the uniformity was better.The ultimate tensile strength of the joint by LWFW was lower than that by LBW slightly,which reached to 73.03% and 79.22% of the base metal respectively.However,the elongation of the LWFW joint was higher than that of the LBW joint significantly,which reached to 38.65% and 20.38% of the base metal respectively.The microstructure and mechanical properties of 5A90 Al-Li alloy by LWFW were better than that by LBW.The defects of joint were mainly forming defects which were caused by improper parameters and porosity inside the joint,which was caused by uncleaned surface and incomplete penetration.     

Comparison of Microstructure and Residual Stress Between TIG and MAG Welding Using Low Transformation Temperature Welding Filler

A Cr–Ni type of low transformation temperature(LTT) welding filler was devised in the present study. The LTT weld microstructures of the tungsten inert gas(TIG) and metal active gas(MAG) weldings were investigated by using electron-backscattered diffraction and orientation imaging microscopy. The results showed that the LTT weld microstructures prepared by TIG and MAG weldings were primarily martensite with 17.5% and 8.0% retained austenite,respectively. The LTT weld metal using TIG welding had larger grain size than using MAG. In addition, based on the Taylor factor calculation, the weld metal using MAG welding was more competent in repressing fatigue crack initiation.Meanwhile, the high angle and coincidence site lattice grain boundaries were dominant in the LTT weld metal using MAG welding. Moreover, the hardness of the LTT weld metal using MAG welding was higher than that of using TIG. Based on heat input and phase transformation, finite element method was applied to analyzing the tensile residual stress(RS)reduction in welded joints prepared by both conventional and LTT welding fillers, respectively. The corresponding outcome confirmed that the LTT weld metal using MAG welding was more beneficial to tensile RS reduction.     

Study on diffusion welding SiCp/ZL101 with Cu interlayer

Through the vacuum diffusion welding SiCp/ZL101 aluminum with Cu interlayer,the effect of welding parame-ter and the thickness of Cu on the welded joint property was investigated,and the optimal welding parameters were putforward at the same time.The microstructure of joint was analyzed by means of optical-microscope,scanning electron mi-croscope in order to study the relationship between the macro-properties of joint and the microstructure.The results showthat diffusion welding with Cu interlayer could be used for welding aluminum matrix composites SiCp/ZL101 successfully.     

Microstructure and mechanical properties of the joint of 6061 aluminum alloy by plasma-MIG hybrid welding

Plasma-MIG (metal inert gas arc welding) hybrid welding of 6061 aluminum alloy with 6 mm thickness using ER5356 welding wire was carried out.The microstructures and mechanical properties of the welded joint were investigated by optical microscopy,X-ray diffraction (XRD),energy dispersive spectroscopy (EDS),tensile test,hardness test and scanning electron microscope (SEM) were used to judge the type of tensile fracture.The results showed that the tensile strength of welded joint was 142 MPa which was 53.6％ of the strength of the base metal.The welding seam zone was characterized by dendritic structure.In the fusion zone,the columnar grains existed at one side of the welding seam.The fibrous organization was found in the base metal,and also in the heat affected zone (HAZ) where the recrystallization occurred.The HAZ was the weakest position of the welded joint due to the coarsening of Mg2Si phase.The type of tensile fracture was ductile fracture.     

Friction stir welding of AZ31 magnesium alloy

Friction stir welding (FSW) is an new solid-phase joining technology which has more advantages over fusion welding methods in welding of aluminum and other non-ferrous metals. The effects of welding parameters on mechanical properties and microstructure during friction stir welding of AZ31 magnesium alloy were studied in this paper. Microstructures and mechanical properties of the joints were investigated by means of optical microscopy, scanning electric microscopy ( SEM ) , micro-hardness analysis, and tensile test. Experimental results show that the magnesium alloy can be successfully welded by FSW method, and the ultimate tensile strength (UTS) of FSW joint reaches up to 90 percent of base metal. The microstructures of welded joints exhibit the variation from dynamically recrystallized fine grains to greatly deformed grains. Hardness in nugget zone was found lower than the base metal but not too obvious.     

The Dissymmetry of Friction Stir Welding Joints and Va-riable Polarity Plasma Arc Welding Joints Study

2219 aluminum alloys welding joints were prepared by Friction stir welding (FSW) and Variable polarity plasma arc welding (VPPAW).The microstructure of joints was characterized by means of OM,SEM,and EDX.Microhardness measurements was performed to differentiate the joint zones and to evaluate the symmetry level of the joints with the help of nano-indentation experiment.The dissymmetry of microstructure and mechanical properties was found both in FSW joint and VPPAW joint.The dissymmetry in FSW joint can not be suppressed due to the nature of the mixing head,but the symmetry and satisfactory welding joint can be obtained by changing the working pattern of VPPAW.     

Microstructure and properties of Nd:YAG laser welded AZ31B magnesium alloy

Biodegradable magnesium-based alloys are very promising materials for temporary implants. Laser welding is an important joining method in such application. In this study, the as-rolled AZ31B magnesium alloy sheets of 1 mm in thickness were successfully joined by Nd ： YAG laser welding. The microstructure and properties of the welded joint were investigated. The result shows that the welded joint is characterized by a narrow heat-affected zone, finer grains and a large number of precipitates distribute in the matrix in the weld. Microhardness of the weld is significantly improved to 72 HV 0. 05 as compared to 55 HV 0. 05 of the base metal. Tensile strength of butt-welded joint is 180. 24 MPa, which is 76. 8% that of the base metal. The electrochemical corrosion experiment shows that the corrosion resistance of laser welded joint is significantly improved in a 3.5 wt. % NaCl solution.     

Characteristics of 5A90 Aluminum-lithium Alloy by YAG-MIG Hybrid Welding

The characteristics of 5A90 Aluminum-Lithium alloy by YAG laser and MIG arc hybrid welding (Hybrid welding) were studied.Compared with the laser beam welding (LBW),the hybrid welding could not only improve the weld appearance significantly,but also have better engineering compatibility.The obvious microstructure characteristics of joint by the hybrid welding are fine-grained layer near fusion-line and the equiaxed grain in most area of welded seam.The subgrains of the equiaxed grains,located in the weld center,tend to coarse from bottom to top of weld joint.The microhardness of welded seam by the hybrid welding (83.57HV0.2) is lower than that by LBW (95.65HV0.2),but the uniformity of the former is better than that of the latter.The ultimate strength and the elongations after fracture of the joint by the hybrid welding are lower than that by LBW.The tensile fracture always occurs in HAZ or weld centerline,and the fractography presents mixture rupture.Therefore,if the combined mechanical properties of joint by the hybrid welding meet the operation requirements,it should be improved by reasonable artificial aging or heat treatment after welding,and it also should develop a better filler wire matched with the base metal.     

TC4钛合金电弧超声TIG焊

进行了TC4电弧超声TIG焊接与传统TIG焊，利用X射线探伤检测接头质量，金相显微镜和SEM观察接头组织和断口，利用万能试验机测试接头拉伸性能。结果表明，严格按照航空标准进行TC4常规TIG焊与电弧超声TIG焊，所获得的接头均达到航空一级；随着加入超声频率的增加，激励电压的增大，电弧超声TIG焊焊缝组织细化、等轴化，枝晶破坏痕迹不明显，接头抗拉强度、屈服强度和延伸率均有所提高。     

Ti-6Al-4V钛合金超音频脉冲TIG焊

进行了Ti-6Al-4V钛合金超音频脉冲氩弧焊(U-TIG)与传统TIG焊,利用X射线探伤检测接头质量,金相显微镜和SEM观察接头组织和断口,利用万能试验机测试接头拉伸性能.结果表明,U-TIG焊能减少焊缝气孔;随着加入脉冲频率的增加,U-TIG焊焊缝组织细化、等轴化,当脉冲频率为45kHz时,晶粒细化效果最好;随着脉冲频率的提高,接头抗拉强度、屈服强度和断后伸长率均有所提高;常规TIG与U-TIG焊接头断口均为准解理断裂机制,但U-TIG断口枝晶破坏痕迹已不明显.     

Study on Ultra-sonic Frequency Pulse TIG of Titanium Alloy

Ti-6Al-4V alloy is used extensively in aerospace and aircraft because of its excellent comprehensive properties and outstanding machinability. Ti-6Al-4V alloy was welded by conventional tungsten iner-gas arc welding (TIG) and ultra-sonic frequency pulse TIG welding (U-TIG) respectively. The welding quality was tested by X-ray, and the mechanical properties of welded joint were tested , the microstructure and the fracture appearance of welded joint were observed by means of optical microscope and SEM .The re...     

薄板TC4钛合金TIG电弧和激光焊接接头晶粒尺寸与微观组织

对薄板TC4钛合金进行TIG电弧和激光焊接技术研究,重点分析了TIG焊接电流、焊接速度和激光输出功率对TC4钛合金焊接接头晶粒尺寸、微观组织和显微硬度的影响规律. 试验结果表明,在实现薄板TC4钛合金完全熔透的条件下,激光焊接具有更小热输入,接头焊缝区和热影响区宽度也显著降低. TIG焊接接头晶粒尺寸随热输入增加,呈现增加趋势. 随距焊缝中心位置增加,焊接接头晶粒尺寸均逐渐降低. TC4钛合金激光焊接接头焊缝区呈现魏氏组织特征,针状α'马氏体细小. 近缝热影响区组织为网篮状α'马氏体,而近母材热影响区为未转变α相和针状α'马氏体的双相组织. 随距焊缝中心位置增加,马氏体生成量逐渐减少,焊缝显微硬度值呈现降低趋势;同时相比于TIG焊接,TC4激光焊接接头具有更高的显微硬度.     

微量CO2对MGH956合金超声电弧TIG焊的影响

对MGH956合金进行超声电弧TIG焊接,在纯氩气保护中添加一定比例的CO₂,通过对比在保护气体中添加0.5%的CO₂前后焊缝组织和接头性能的变化,分析了在超声电弧的基础上微量CO₂对焊缝组织及接头性能的作用机制及影响规律.结果表明,施加超声电弧后,焊缝晶粒变小,气孔变少,焊缝的抗拉强度有所提高;在施加超声电弧的基础上,在纯氩气中加入0.5%的CO₂,焊缝中心晶粒呈细小等轴晶,且分布均匀,接头的抗拉强度明显提高,并实现了接头断裂方式由脆性断裂转化为韧性断裂.此外在纯氩气中加入0.5%的CO₂后,焊缝的硬度增加,接头的综合性能得到了提高.     

热碾压对AZ31镁合金焊接接头组织和性能影响

采用交流钨极氩弧焊和热碾压装置对AZ31变形镁合金进行焊接试验和热碾压试验;利用光学显微镜、扫描电镜(SEM)、显微硬度计、电子拉伸试验等手段对焊接接头的显微组织、元素分布、断口形貌、接头硬度和强度等进行分析。结果表明:热碾压熔焊接头的抗拉强度可达225 MPa,为母材金属的90%以上,而焊态下熔焊接头的抗拉强度仅为母材金属的60%左右;热碾压焊接试样的伸长率(9%～11%)均高于焊态试样的(6%～8%);热碾压接头断口呈现一定的准解理断裂特征,且可以观察到热碾压塑性变形流变线,而焊态断口呈现以解理断裂为主的断裂机制,同时伴随有极少量的韧窝断裂特征。     

超声电弧对6061铝合金MIG焊接头组织和性能的影响

为了改善铝合金MIG焊的接头质量，利用外接超声激励装置在MIG焊接电弧中激发出超声，并研究了超声激励频率对6061铝合金对接焊缝的成形、气孔分布、显微组织及力学性能的影响规律. 结果表明，超声电弧可以有效的细化焊缝组织、减少焊缝气孔量，提升接头的强度. 与常规MIG焊接相比，在引入超声电弧后，焊缝的熔宽增加，焊缝中胞状树枝晶组织被细化，等轴晶区域占比增加，在激励频率为30 kHz时组织细化效果最好；随着激励频率的增加，焊缝中的气孔量逐渐降低，焊接接头的抗拉强度提高，当激励频率为50 kHz时，抗拉强度最高，达到235 MPa，为母材强度的73.4%，对应拉伸断口中韧窝的形态更加等轴化、分布更加均匀.     

High speed tandem TIG welding of ferritic stainless steel plate

Weld humping and undercut are the most common appearance defects in high speed welding. A high speed tandem TIG welding process was developed to suppress the formation of these appearance defects and to improve the productivity of TIG welding. In this paper, the mechanical properties and microstructure of joints obtained from tandem and single TIG welding were tested and compared. The results show that the sound weld appearance can be obtained by tandem TIG welding at the welding speed of 3 m/min for 1.5 mm thick 409L stainless steel plate. The mechanical properties of the tandem TIG welded joint are in the similar level with single TIG welded joint. The analysis of the tandem TIG welding process indicates that the assistant arc with a push angle can prevent the liquid metal flowing backward to the trailing region of weld pool and the premature solidification of thin liquid layer in the gouging region.     

Microstructure and porosity analysis in ultrasonic assisted TIG welding of 2014 aluminum alloy

The ultrasonic assisted tungsten inert gas (U-TIG)welding is a newly developed arc welding method,which is aimed at improving the weld quality and efficiency.TIG welding and U-TIG welding of 2014 aluminum alloy with 5 mm thickness were experimentally carried out in this paper.The microstructure and porosity of welded joints were analyzed.Compared with conventional TIG welding,the columnar crystals are changed into equiaxed crystals at the centre of weld zone and the grain of fusion zone in U-TIG welding is refined and equiaxed.The porosities of joint decrease after the ultrasonic was applied on the arc.The mechanism of crystal grain refiaement is discussed in this paper and the reasons of porosity decrease in U-TIG welded joint may be due to the effect of acoustic streaming and cavitation,which need further research.     

304不锈钢薄板列置双TIG高速焊缝组织与性能

相比常规速度不锈钢焊接,高速焊接过程中焊缝金属的凝固过程及组织形态将会发生变化,从而影响焊缝组织和性能. 对1.2 mm厚304不锈钢薄板对接,采用列置双TIG焊在焊接速度为3.0 m/min时获得了良好焊缝成形,并与常规速度单TIG焊接工艺相比,采用非标准拉伸试样测试了焊缝性能,并分析了其组织. 结果表明,高速双TIG焊接焊缝中心生成等轴晶,两侧树枝晶未形成对向生长的定向晶粒,焊缝抗拉强度及断后伸长率略低于母材;相比常规单TIG焊接工艺,高速双TIG焊接热影响区晶粒平均直径降低了10.3%,但焊缝中心晶粒平均直径增大了12.9%;焊缝抗拉强度和断后伸长率分别提高了4.3%和23.2%,焊缝中心硬度值略高于母材.