Characteristics of arc in variable polarity plasma arc welding of aluminum alloy

A double invert variable polarity plasma arc （VPPA） power source based on 16-bit MCU applied for aluminum alloys was developed. Mechanics, electrical and the produced heat mechanism of VPPAW arc were tested and analyzed. Results indicate that during the VPPA welding procedure of aluminum alloy, the arc of electrode negative （EN） has more effect on force, whereas the arc of electrode positive （ EP ） has more effect on heat. It should be noted that keeping the balance of the force and heat is the critical element of VPPAW. This power source had been successfully used to weld aluminum alloy with a 15 mm thickness in vertical welding. The conclusions are applicable to the variable polarity plasma arc welding technique used in the aerospace industry.     

Optimization of HPVP-GTAW process parameters for Al-Mg aluminum alloy welded joints

Optimization of hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process was carried out to obtain the optimum weld characteristics of 5AO6-HX4 aluminum-magnesium alloy sheets of 3 mm thickness. The square butt joints were produced by HPVP-GTA W process, the microstructure and mechanical properties were systematically investigated. It is observed that the process parameters influence the weld microstructure and mechanical properties significantly. Weld microstructure is mainly composed of grid a （A1） solid solution, with a large number of intermetallic （ Mg2Al3 ） precipitates distributed in the matrix. The amount of ~ （ Mg2Al3 ） precipitates has an obvious difference with different parameters. Compared with that of the base material, tensile strength of 5AO6-HX4 alloy welded joints has a certain reduction, as well as the elongation and reduction of area. The optimized welding process parameters for 5A06-HX4 alloy sheets are presented.     

Effect of variable polarity frequency on 2A14-T6 aluminum alloy welds using HPVP-GTAW process

Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse current frequency 40 kHz on weld bead geometry, microstrueture and microhardness were analyzed. Experimental results indicate that, compared to that of the conventional VP-GTAW process, the weld depth and ratio of weld depth to width are improved significantly by the variable polarity frequency in the HPVP-GTAW process, which the ratio of weld depth to width is improved by 36% at equal variable polarity frequency of 100 Hz, and improved by 55% with that of 200 Hz. Weld microstructure and microhardness distribution are changed obviously with the increase of variable polarity frequency. In the conventional VP-GTA W process, the grains in weld central zone are coarser, and the microhardness in weld central zone and fusion zone is about 95 HV and the lowest 82 HV, respectively. The microhardness is enhanced to a certain extent both in the weld central zone and fusion zone with the variation of variable polarity frequency in the HPVP-GTAW process due to the refinement and uniformity of weld microstructure. With the variable polarity frequency of 600 Hz, the microhardness in weld central zone and fusion zone reaches nearly 110 HV and 97 HV, respectively.     

2A14铝合金变极性等离子横向焊缝成形特点

对6 mm厚2A14铝合金变极性等离子弧横向焊接的难点及焊接工艺参数的特点进行了研究,通过横向焊穿孔熔池受力分析,阐释了变极性等离子横向焊缝成形缺陷产生的原因.变极性等离子弧横向焊接的难点是焊缝正面和背面的咬边缺陷及焊缝上部(靠近熔合线)宏观气孔的聚集.稍小的焊接线能量有利于消除横向焊缝正面咬边缺陷,稍大的焊接线能量有利于消除焊缝背面咬边缺陷.分析认为变极性等离子横向焊缺陷的产生与穿孔熔池受力平衡及重力方向改变导致的流动密切相关.     

变极性等离子电弧力学行为研究

研究了变极性等离子孤焊接工艺参数对变极性等离子电孤力的影响规律,提出了变极性等离子电孤的力学特性,它是变极性等离子电孤的重要特性之一,试验结果对中厚板铝合金变极性等离子孤焊接工艺稳定性以及焊接过程控制有重要的指导意义。     

铝合金变极性等离子弧穿孔焊过程控制

分析了铝合金变极性等离子弧穿孔立焊工艺特点,提出了通过对焊接参数的精确控制,实现变断面铝合金变极性等离子弧穿孔立焊工艺的方法,并将焊接电流、离子气流量和焊接速度确定为变断面铝合金变极性等离子弧穿孔立焊过程的被调节参数.保持穿孔熔池上"热"和"力"的动态平衡是调节焊接参数的根本依据,是实现变断面试件自动焊接的关键所在.采用单片机为核心的控制器对焊接参数进行实时调节,动态保持穿孔熔池上热和力平衡,实现了变断面铝合金变极性等离子弧穿孔立焊工艺.     

铝及铝合金的变极性等离子焊接设备与工艺

通过铝及铝合金焊接特点的分析,比较TIG、MIG、PAW不同焊接方法的优缺点;对不同板厚的防锈铝进行大量的变极性等离子焊接工艺试验,总结出变极性等离子焊接铝合金开设备的要求,以及分析等离子焊接工艺参数对成形的影响,制定了一套成熟的焊接工艺参数。试验结果表明：立焊变极性等离子焊接中厚板铝及铝合金有着明显的工艺优势,可以实现单面焊双面成形,焊前清理要求低,焊缝可达到Ⅰ级。     

VPPAW工艺的变极性焊接电流受控稳定性

在铝合金的变极性等离子弧焊(variable polarity plasma arc welding,VPPAW)工艺中,变极性焊接电流的受控稳定性是确保焊接成形质量的前提. 然而,等离子电弧形态会随焊接电流极性的切变而变化,使得等离子电弧作为VPPAW电源的输出负载具有显著的非线性特性,常规比例积分微分(proportional integral derivative, PID)控制策略无法确保VPPAW电源输出电流波形畸变,而输出焊接电流波形的畸变又会进一步加剧电弧负载的非线性特性,降低变极性焊接电流的受控稳定性. 为了改善VPPAW工艺的变极性焊接电流的受控稳定性,研究了常规PID控制策略下铝合金的变极性等离子弧穿孔立向上焊接工艺的焊接电流受控稳定性以及等离子电弧的动态稳定性,引入了模糊控制理论,基于现场可编程门阵列(field programmable gate array, FPGA)的并行逻辑时序设计方法,设计出了一种具有并行运算能力的模糊PID控制器. 验证试验结果表明,具有并行运算能力的模糊PID控制器能够有效地改善VPPAW工艺的变极性焊接电流波形的受控稳定性.     

Numerical analysis of temperature profile and weld dimensions in laser ＋ GMAW hybrid welding of aluminum alloy T-joint

The temperature fields in the transient state and weld dimensions in laser ＋ gas metal arc welding （GMAW） hybrid welding of aluminum alloy T-joint for different welding conditions were calculated using the developed heat source model, and the effect of welding speed on them was analyzed. The results show that the temperature field for the first weld pass only shows the feature of GMAW and the one for the second weld pass has the characteristics of both laser welding and GMAW. Welding speed can affect greatly weld dimensions and temperature distribution. When welding speed reaches 3.5 m/min, the fusion zones of two weld passes are separated and the maximum peak temperature of thermal cycle on the workpiece surface decreases largely.     

铝合金变极性等离子弧焊接工艺中的双弧现象

在铝合金变极性穿孔型等离子弧焊接工艺中，维弧电源对变极性电弧的稳定和工件受力状态有显著影响。在反极性时间内，部分主电流会通过维弧电源在喷嘴和工件之间形成自由电弧，产生双弧现象，增大喷嘴的烧损，同时，双弧的产生减小了反极性期间的等离子电弧力，使得电弧的穿透能力减小。     

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.     

变极性等离子电弧形态对电弧力的影响

研究了变极性等离子弧焊接工艺中,电弧形态及力学行为随焊接过程变化的现象,提出了变极性等离子电弧力学行为随电弧形态的改变而变化的规律。通过高速摄像以及对电弧力和电流的同步检测,证实了联合型等离子弧在反极性时间内易形成双弧的事实。     

Microstructure characteristics of dissimilar metal weld between aluminum alloy and brass

Dissimilar metal joining between 5A02 aluminum alloy and H62 brass sheets was conducted by gas tungsten arc welding with Zn-15% Al and Al-12% Si flux-cored filler wires. The microstructure in the weld and distribution of major alloying elements in the intelfacial layer were examined, and the tensile strength of the resultant joints was measured. Pores appeared in the weld made with Zn-15% Al flax-cored filler wire, the interracial layer mainly consisted of AlCu phase, and the specimens fractured through the weld with tensile strength of 129 MPa. When Al-12% Si flux-cored filler wire was used, Cu diffused into the weld and Al2 Cu phase formed, and the specimens fractured along the interfacial layer with tensile strength of 122 MPa.     

Pulsed TIG welding-brazing butt joints of aluminum-stainless steel thin plates with different fillers

Aluminum and stainless steel plates with 1.5 mm thickness are joined by pulsed TIG welding-brazing process with ER1100, ER4043 and ER2319 fillers, separately. Good weld formation can be obtained by adjusting appropriate pulse parameters. The effects of the fillers on that the thickness of the intermetallic compound （ IMC ） and tensile strength of the joints are investigated. SEM results indicate layer with ER2319 filler is about 2 ~m, which is thinner than 2. 5 p~m of ER1100 filler and 3.5 txm of ER4043 filler. Moreover, the element distribution in both IMCs and welded seams with three fillers are different because of the different compositions of fillers. The results of mechanical property tests suggest that the joint strength with ER2319 filler is the highest, while the joint impact energy is the lowest. The joint with ERllOO filler exhibits the best comprehensive mechanical pet.formanee.     

Exploring material flow in friction stir welding using stacked structure of 2024 and 6061 aluminum alloys

An experimental technique based on stacked structures was developed to observe the material flow behavior of the friction stir welding （FSW） process. Analysis of section views along different directions revealed important new details of the material flow in FSW process. In this work, a general flow model of FSW was constructed based on the analysis of different static section views of stacked structure weld. The formation of onion rings was found to be a geometric effect due to layered deposition attd the extrusion occurred at the interface between flow arm （FA） and stirring zone （SZ）.     

TIG welding-brazing joint of aluminum to stainless steel with hot wire

TIG welding-brazing process with high frequency induction hot wire technology was presented to create joints between 5A06 aluminum alloy and SUS32! stainless steel using ER1100 filler wire with different temperature. The joints were evaluated by mechanical test and microstructural analyses. The welding procedure using hot fiUer wire （400 ℃ ） significantly increases strength stability by 71% and average value of tensile strength by 30. 8 % of the joints, compared with cold wire. The research of microstructures in interfaces and welded seams reveals that using 400 ℃ hot filler wire can decrease the thickness of intermetallic compounds （ IMCs ） from 6 to 3.5 txm approximately, which is the main reason of mechanical property improvement.     

一种实现变极性焊接电流波形的新方法

介绍了一种实现变极性焊接电流波形的新方法。正、负半波电流分别供电，在主弧负半波以冷却良好的铜喷嘴代替钨棒作阳极，既满足了对铝工件氧化膜清理的需要，又降低了钨电极的烧损，实现了稳定的变极性焊接过程。     

铝及铝合金先进焊接技术

分析了铝及铝合金的焊接性及其在焊接过程中易出缺陷(气孔、热裂纹等)的原因和解决措施;探讨了铝及铝合金的几种先进焊接工艺(激光焊、电子束焊、变极性等离子电弧焊、搅拌摩擦焊等)的研究现状及其应用;分析了铝及铝合金焊接技术的发展状况以及未来几年的前景。     

电流换向速率对2219铝合金VPTIG焊缝的影响

研究开发了一种适用于铝合金材料的新型超快速变换变极性方波电弧焊接技术,以2219-T87高强铝合金为试验对象,分别采用常规变极性和超快变换变极性TIG电弧焊接工艺,研究了变极性电流的换向速率对焊缝气孔敏感性和接头力学性能的影响.结果表明,提高变极性电流上升沿和下降沿的变化速率,减少电流过零时间,可显著降低2219-T87高强铝合金焊接接头的气孔敏感性,焊缝中气孔数量明显减少甚至消除;由于焊缝熔合区的软化问题,焊接接头抗拉强度和断后伸长率的增加幅度不大,分别提高了8.97%和12.6%.     

Changes of microstructure of different quench sensitivity 7,000 aluminum alloy after end quenching

The quench sensitivity and their influential factors of 7,021, 7,085, and 7,050 alloys were investigated by the end quenching test method and the measurement of electrical conductivity, hardness, and microstructure after aging. The results indicate that 7,050 alloy has the largest changes with hardness decreasing from HV 199 to HV 167,and electrical conductivity increases from 16.6 to18.2 MS m-1when the distance from quenched end increases from 2 to 100 mm. Alloys 7,085 and 7,021 have relatively smaller changes. According to the relationship between the hardness and electrical conductivity of a supersaturated solid solution, 7,050 alloy has higher quench sensitivity than 7,085 and 7,021 alloys. The microstructure of 7,050 alloy with higher major alloy element(Zn + Mg + Cu) addition and Cu element addition is mostly affected by the changes of distance from quenched end. In 7,050 alloy, the size of intragranular precipitates is from about 10–200 nm, and the(sub) grain boundary precipitates are about 20–300 nm. Alloy 7,085 with lower Cu content is moderately affected, while 7,021 is least affected. It is found that with the increase of distance from quenched end, quenched-induced precipitate preferentially nucleates and grows in the(sub) grain boundary and then on the pre-existing Al3 Zr particles.