MIG自动焊在铝镁合金焊接中的应用

GIS是一种气体绝缘全封闭开关设备 ,将各组成元件装入密封的金属接地罐体内 ,并在此罐体内充入作为绝缘及灭弧介质的SF6气体 ,是电力输送的关键设备。公司于 1998年开始进行 12 6GIS新产品的研制。为减少涡流及减轻重量 ,金属接地罐体材质选用铝镁合金板材和铸件。参考国外同行焊接工艺 ,日本东芝利用焊接机器人采用双丝MIG焊。日本三菱采用混合气保护的MIG自动焊。瑞士ABB采用等离子弧焊接。都取得了良好的焊接质量 ,实现了高效率化。公司开始采用的是手工氩弧焊 (TIG) ,为满足GIS产品产量的迅速增加 ,保证罐体类部件的供给 ,必…     

Tandem MIG welding of aluminium alloys

Welding processes used in transport system manufacturing, such as the automotive industry, have in recent years seen a pronounced trend towards fabrication of lower-cost welded structures through efficiency enhancement focused on weld quality improvement. In this context, arc welding processes providing sufficient weld reinforcing ability, while allowing higher-speed welding are expected to emerge. In welding of aluminium alloys, MIG welding conferring superior economy and profitability holds out particularly high expectations, in future set to be the mainstream process for fabrication of welded structures. In MIG welding, however, straightforward adoption of higher welding speeds for efficiency enhancement purposes leads to loss of joint quality and weldpool turbulence due to increased current. Welding speeds therefore normally have an upper limit of around 1.5 m/min.¹ More recently, however, further welding speed increases have been sought through improvement of wire feed¹ and power supply² systems.     

Self-adjusting dynamic characteristics of pulsed MIG welding for aluminum alloys

Pulsed MIG welding is suitable for aluminum alloys welding, because spray transfer and excellent profile can be arrived during whole welding current range, and the energy of droplet can be controlled to overcome losing of alloy elements with lower melting and steam point by controlling pulse current and pulse time. Because of the special physic properties of aluminum alloys, there are different requirements for pulsed MIG welding between starting arc short circuit and drop transfer short circuit, pulse period and base period. In order to satisfy the need of aluminum alloys MIG welding, self-adjusting dynamic characteristics are designed to output different dynamic characteristics in different welding startes. The self-adjusting dynamic characteristics of pulsed MIG welding are achieved through a short circuit controller and a dynamic electronic inductor. The welding machine(AL-MIG 350) with self-adjusting dynamic characteristics has a high rate of successfully starting arc up to 96%, and the short circuit time during transfer is less than 1ms, in the mean time, the arc is stiffness, spatter is low and weld appearance is good.     

铝合金可变双脉冲MIG焊接工艺

针对恒规范铝合金焊接时,随着母材热输入的增加,母材热积累效应会不断增强,焊缝熔宽会随之变宽甚至出现焊塌的问题,采用基于xPC Target的实时目标环境,设计了铝合金可变双脉冲MIG焊试验平台,并进行了铝合金可变双脉冲MIG焊接工艺方面的试验研究。试验结果表明:当双脉冲中的低能脉冲在每个周期中所占的比例从0%不断增加到80%时,通过降低每个周期的平均电流而减少的母材热输入,可以补偿母材增强的热积累效应,从而有效地控制焊缝熔宽。焊缝成形美观,焊接效果良好。     

铝合金MIG焊机的辅助控制系统

针对铝合金MIG焊易形成引弧点未熔合、焊缝成形不良、弧坑裂纹和易氧化缺陷的问题，进行了铝合金MIG焊机的辅助控制系统设计。     

Microstructures developed during steady-state creep of Al-Mg alloys

The microstructures developed during steady-state creep of Al-Mg alloys containing 1.77–7.72 at.% Mg were examined using optical and electron microscopy. Subgrains were found in specimens crept at lower stresses where the stress exponent is about 3, and viscous glide is considered to be rate controlling. This is contrary to normally accepted mechanisms where subgrains and cell structures are considered to be formed only when recovery is rate controlling and the stress exponent is approximately 5. However, because the subgrains were also found in the head sections (unstrained), the presence or absence of subgrains merely reflects the condition prior to testing, rather than that developed during creep. The size of the grains and subgrains decreases with increasing creep stress and/or magnesium content. An Al₃Mg₂ precipitate has been identified in the Al-7.72 at.% Mg alloy after creep and is considered to give rise to the higher stress exponent of steady-state creep (n ∼ 4) for this alloy.     

焊接烟尘发尘机理及其影响因素

详细地阐述了焊接烟尘形成的蒸发、凝结、长大机制以及其形成后的扩散方式,对典型的焊接材料的烟尘性质进行了分析,介绍了有毒有害气体产生的原因和方式,对影响焊接烟尘产生的材料因素和工艺因素进行了分析.     

Analysis of interface solid-state reaction on dissimilar ultrasonic spot welding of Al-Mg alloys

The solid-state joining nature of the ultrasonic spot welding (USW) process has been proven useful in the fields where joining applications involve dissimilar lightweight materials. This study focused on the USW of challenging dissimilar aluminum (Al)-magnesium (Mg) alloys to gain a better understanding of the dominant factors of joint performance with particular emphasis on proper lap-joint positioning. Weld qualities of dissimilar ultrasonic spot welds, classified through a series of experiments, were determined. Process parameters effects, such as failure load and fracture morphologies, showed distinctions between two dissimilar welds based on lap-joint position. Characteristic distinctions between welding process parameters and material combinations (lap-positioning) were found. Incomplete deformation zones were found during USW of Mg/Al combination, yet they were noticeable and almost the same size as the horn diameter. It can be found that proper lap-positioning of the top part of the specimen is important for efficient utilization of the USW process.     

Mechanical spectroscopy of Al-Mg alloys

The internal friction of deformed, annealed, and quenched Al-Mg alloys with Mg contents of 0–12 wt % has been studied as a function of temperature. The measurements have been performed in the range of 25–580°C at 0.3–30 Hz using a DMA Q800 TA Instruments dynamic mechanical analyzer at the maximum amplitude of deformation ?₀ = 5 × 10^?5. In annealed alloys with Mg contents up to 5 %, a relaxation IF peak with activation parameters (activation energy H ≈ 1.7–2.1 eV) has been detected. In alloys with 8–12% Mg, this relaxation peak is absent and, at a lower temperature, another IF peak appears (with an activation energy H of about 1 eV), which is interpreted as the Zener peak in terms of the combination of activation parameters. The article discusses the nature of these peaks and the influence of alloying on the relaxation mechanisms. In cold-worked alloys, an IF pseudo-peak takes place, which is related to the recrystallization of samples, and its temperature position in the alloys that contain more than 5% Mg depends not only on the degree of deformation, but also on the dissolution temperature of the β phase.     

High-temperature oxidation of Al-Mg alloys

Surface-analysis techniques (x-ray photoelectron spectroscopy and Auger electron spectroscopy) and electron microscopy (SEM and TEM) have been used to study the mechanism of steady-state high-temperature oxidation of Al-Mg alloys. Two high-purity alloys containing 0.4 and 2.0 wt.% Mg were heat-treated in dry air at 550°C up to 90 hr. It was found that the oxide layer was composed of MgO and spinel (MgAl₂O₄), the major constituent being MgO. The molar concentration of MgO decreased with increasing depth, while that of spinel increased. The rate-controlling mechanism for the growth of the oxide layer in the Al-0.4Mg alloy was the solid-state diffusion of Mg in the MgO-spinel constituents. For alloys of higher-magnesium content, the growth of the oxide layer was controlled by solid-state diffusion of Mg through the adherent protective oxide areas and by the transport of Mg vapor across voids formed between the alloy substrate and the oxide layer.     

电渣焊

描述 电渣焊是一种在垂直位置或接近垂直位置使用的高效单道焊过程，用于连接厚度大于25mm的钢板或部件。20世纪50年代初，乌克兰的巴顿电焊研究所发明了电渣焊，并用它代替大电流埋弧焊过程来焊接厚壁压力容器上的纵向焊缝。     

Evaporation phenomena of magnesium from droplet at welding wire tip in pulsed MIG arc welding of aluminium alloys

Abstract

A lot of welding fumes are generated due to the evaporation of magnesium during welding aluminium alloys using Al–Mg welding wires. Fume formation is mainly evaluated by two methods. An average formation rate can be calculated by collecting the fumes formed during a constant welding period. The other one is carried out by observing the droplet with a high speed video. However, these two methods become invalid in quantitatively evaluating the evaporation rate of magnesium in peak or background period during pulsed metal inert gas arc welding. In this paper, a novel method was developed to evaluate the evaporation rate and flux of magnesium in the peak period. First, a robot welding system was used to produce a series of droplets by shutting down the peak current at different times in the peak period. Second, the magnesium contents of these droplets were analysed. Finally, the evaporation rate and flux of magnesium in the peak period were calculated.     

AC MIG与DC MIG焊接工艺及控制的分析

比较分析了DCEP P MIG焊与DCEN MIG焊的焊接现象,在此基础上,解释了研究开发AC P MIG焊的意义。AC P MIG焊克服了DCEP MIG焊时容易产生的磁偏吹现象,且比DCEP P MIG焊的焊丝熔化速度快、焊缝熔深浅。AC P MIG焊有多种电流模式,其交流电流负极性比率AC I EN％主要用于控制焊缝熔深,其交流电流正极性脉冲Ip主要用于控制熔滴过渡,最理想的是1周1脉1滴的熔滴过渡形式。根据有关的研究表明,在相同送丝速度的条件下,AC P MIG焊的焊缝熔深随AC I EN％增加而减小,焊缝表面光泽好,焊丝熔化金属热含量低等,这些特点最适宜用于焊接薄板。     

A5083P-O铝合金MIG焊接接头组织及疲劳性能研究

A5083铝合金为Al-Mg系防锈型铝合金,不可热处理强化,塑性较好,但强度较低,其耐蚀性和焊接性良好,退火状态时切削加工性较差。研究4 mm厚度A5083P-O MIG焊接接头的组织、硬度及其疲劳强度,发现接头的焊缝组织主要是以细小的枝晶为主,熔合线靠母材侧为垂直于熔合线的细长柱状晶粒。焊接接头各区域硬度值为70~80 HV,热影响区的软化现象不明显。接头的条件疲劳强度能够达到95 MPa。     

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al-Mg alloys

The mechanisms involved in the grain refinement of Al-Mg alloys through varying the Mg content and applying intensive melt shearing were investigated. It was found that the oxide formed in Al-Mg alloys under normal melting conditions is MgAl₂O₄, which displays an equiaxed and faceted morphology with {1 1 1} planes exposed as its natural surfaces. Depending on the Mg content, MgAl₂O₄ particles exist either as oxide films in dilute Al-Mg alloys (Mg < 1 wt.%) or as naturally dispersed discrete particles in more concentrated Al-Mg alloys (Mg > 1 wt.%). Such MgAl₂O₄ particles can act as potent sites for nucleation of α-Al grains, which is evidenced by the well-defined cube-on-cube orientation relationship between MgAl₂O₄ and α-Al. Enhanced heterogeneous nucleation in Al-Mg alloys can be attributed to the high potency of MgAl₂O₄ particles with a lattice misfit of 1.4% and the increased number density of MgAl₂O₄ particles due to either natural dispersion by the increased Mg content or forced dispersion through intensive melt shearing. It was also found that intensive melt shearing leads to significant grain refinement of dilute Al-Mg alloys by effective dispersion of the MgAl₂O₄ particles entrapped in oxide films, but it has marginal effect on the grain refinement of concentrated Al-Mg alloys, where MgAl₂O₄ particles have been naturally dispersed into individual particles by the increased Mg content.     

新型MIG焊接技术的发展

将新型MIG焊技术分为脉冲MIG焊、双丝MIG焊和复合热源MIG焊三种主要类型,阐述了研究及发展状况,分别对其工艺特点、适用范围及目前所取得的成就进行了分析,并展望发展趋势。     

变极性脉冲MIG焊接工艺

直流且焊丝为正极性的脉冲MIG焊，电孤稳定，焊缝熔深大，焊接薄板时，为了防止烧穿及熔池下塌。容易产生咬边等焊接缺陷。直流且焊丝为负极性的MIG焊，电弧沿焊丝上爬，电弧不稳定，熔滴不易过渡，焊接熔池浅，容易出现融合不良、凸焊道等焊接缺陷。变极性脉冲MIG焊，焊丝为正极性时控制焊丝熔化及熔滴过渡，焊丝为负极性时电弧沿焊丝上爬促进焊丝熔化及减小电弧对熔池的加热作用，减小焊缝熔深形成浅熔深的特性，焊接薄板具有独特优势，是MIG焊的最新研究进展。