Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg-5Zn-1Mn-0.6Sn alloy sheets of 2 mm in thickness were welded by fiber laser welding. The appearance and microstructures of the welding joints and liquation behaviors in the partially melted zone (PMZ) were investigated. The results show that, with the lower welding power and higher welding speed, the width and depth of the joints decrease. Moreover, some pores are detected at a very high welding speed. There are two kinds of liquation phenomena in the PMZ. One is the liquation network along grain boundaries associated with the liquation of substrate and segregation-induced liquation, the other is the molten pool involved with the liquation of the residual second phases at the boundaries. However, the liquation of substrate and the segregation-induced liquation are the main liquation mechanism in the PMZ.     

ZK60镁合金激光焊接接头的液化开裂(英文)

采用激光对ZK60镁合金板材进行焊接,研究焊接接头半熔化区的显微组织。结果表明:铸态合金半熔化区中沿晶分布的共析混合物在焊接过程中出现液化,其凝固组织呈现亚共晶结构,这种结构导致晶界处的Zn元素偏析更为严重,从而加剧了该区域的开裂倾向;半熔化区液化开裂的主要原因是凝固最终阶段液相不足使得半熔化区液化部位产生缩孔,并成为裂纹源,在凝固收缩及热收缩所产生的拉应力作用下,裂纹沿弱化的晶界扩展;降低焊接热输入和对母材进行轧制等塑性加工均有利于提高该合金焊接时的抗液化裂纹性能,后者的作用主要在于细化共晶相的尺寸并改变其分布。     

Hot cracking in pulsed laser processing of a nickel based superalloy built up by electrospark deposition

A cast precipitation hardened nickel based superalloy was built up by electrospark deposition and then subjected to pulsed laser welding. The resistance of electrospark deposition layer to liquation and solidification cracking in pulsed laser welding was significantly higher than that of the cast alloy. It is shown that the extreme cooling rates involved in the solidification of electrospark deposition droplets result in the prevention of formation of grain boundaries terminal solidification constituents, which are the sources of liquation cracking in the cast alloy.     

Liquation cracking in partial penetration aluminium welds: assessing tendencies to liquate,crack and backfill

Abstract

Aluminium alloys are susceptible to liquation cracking in the partially melted zone (PMZ), where grain boundary liquation occurs during welding. Alloys 2024, 6061 and 7075 were gas-metal arc welded with fillers 1100 and 4043, and liquation cracking near the weld root was examined. Curves of temperature (T) versus solid fraction (f_S), based on the Scheil equation for Al-Cu-Mg-Mn-Si-Zn alloys, were calculated for the solidifying PMZ and weld metal at the fusion boundary. Judging from the freezing temperature range and the liquid fraction, these curves suggested that liquation decreases in the order of 7075, 2024 and 6061, consistent with experiments. They also suggested that 1100 increases the weld metal f_S, thus promoting liquation cracking (by strengthening the solidifying and contracting weld metal that pulls the PMZ) and discouraging backfilling (by reducing the interdendritic liquid), while 4043 does the opposite except during PMZ terminal solidification in 7075 and 2024. These are consistent with experiments.     

Effect of nature of grain boundaries on intergranular liquation during weld thermal cycling of nickel base alloy

Abstract

An Inconel 718 based alloy containing only trace amounts of C, S, and P was subjected to thermal cycling in a Gleeble 1500 system to induce microstructural features which are produced in the heat affected zone (HAZ) during welding. In the thermally cycled material many grain boundaries were observed to liquate; however, the liquation was heterogeneously distributed, that is, only some grain boundaries, and often only a few segments of the same grain boundary, liquated. Orientation imaging microscopy and electron backscatter diffraction analysis in a scanning electron microscope revealed that the liquated grain boundaries or segments of a grain boundary that liquated were always non-special geometry (or random) boundaries, whereas low reciprocal volume density Σ coincident site lattice and twin boundaries did not liquate. Therefore, it is concluded that the extent of B segregation, to which liquation of grain boundaries in the H AZ during welding has been attributed, is greater on random boundaries owing to their ability to accommodate a large number of B atoms in comparison with the low Σ boundaries leading to their liquation during Gleeble simulation.     

Special features of the formation of the microstructure and chemical heterogeneity in welded joints in alloys of the Al–Zn–Mg–Cu system alloyed with scandium

Special features of the formation of the microstructure and the development of chemical heterogeneity in the weld metal and heat-affected zone (HAZ) in arc welding of a complex alloyed alloy of the Al–Zn–Mg–Cu system are discussed. It is shown that the effect of welding heating results in melting of the phase components of the alloy in the HAZ with the formation of structures of the eutectic origin in the form of long interlayers at the boundaries of recrystallized grains, causing brittleness of the metal. Alloying the alloy with scandium reduces the intensity of the processes of recrystallization and the extent of liquation at the grain boundaries and also localizes the melting of the grains without the formation of thick eutectic interlayers.     

薄板2524铝合金激光填丝焊接工艺及组织性能

2524铝合金是具有优异损伤容限的新型航空高强Al-Cu-Mg合金.采用高功率光纤激光器焊接1.6 mm厚2524铝合金,研究了填充5087焊丝情况下,激光功率、焊接速度和填丝速度对焊缝成形、热裂纹倾向和焊缝显微组织的影响,优化焊接工艺参数,考察接头静态拉伸性能.结果表明,采用填充材料后,焊缝柱状枝晶生长方向性明显减小、晶粒细化、晶界共晶增多、热裂纹倾向降低.当激光功率为2.5 kW,焊接速度为2 m/min,填丝速度为2 m/min时,可获得成形良好、无缺陷的焊缝,接头抗拉强度达到313~324 MPa,拉伸断裂于接头熔合线附近,断口处有大量韧窝,呈韧性断裂特征.     

Mechanical properties and microstructures of magnesium alloy AZ31B joint fabricated by resistance spot welding with cover plates

Abstract

The authors welded magnesium alloy AZ31B sheets using the technique of resistance spot welding with cover plates, and investigated the effects of welding parameters on the tensile shear strength of joints and shape characteristic of nugget. The joints with high tensile shear strength were obtained under relatively low welding current. The equiaxed grains with the many intragranularly precipitated particles Mg₁₇Al₁₂ in the nugget were observed.     

Enhancement of AZ80 joints using ultrasonic vibration-assisted welding process

Ultrasonic vibration-assisted welding process was developed to improve the microstructures and mechanical properties of AZ80 Mg alloy joints. Results show that the ultrasonic vibration-assisted welding process has a significant effect on the morphology and size of both β-Mg₁₇Al₁₂ precipitated phases and α-Mg grains. With ultrasonic vibration treatment, the primary α-Mg grains are transformed from coarse dendrites to nearly fine equiaxed grains, and the β-Mg₁₇Al₁₂ phases at α-Mg boundaries are refined and become discontinuous, owing to the cavitation effects and acoustic streaming effects induced by ultrasonic vibration. The mechanical properties of AZ80 Mg alloy joints under the ultrasonic vibration-assisted process are obviously improved. And the influence mechanisms of the ultrasonic vibration-assisted welding process on joints are discussed in detail.     

The constitutional liquation at the interface of Al/Mg friction welding joints

Constitutional liquation occurred at the friction interface of Al/Mg joints produced by continuous drive friction welding. This paper investigated the relationship between constitutional liquation and microstructure morphology of Al/Mg joints. The intermetallic compound γ-Al₁₂Mg₁₇ underwent morphological transitions from submicron-size particles to island-like lamellae, then to network structure as the Al content increased. The submicron-size γ-Al₁₂Mg₁₇ particles precipitated along the grain boundaries of α-Mg solid solution. The Mg–Al₁₂Mg₁₇ divorced eutectic structure was formed. The formation mechanism of eutectic structure was studied with Al–Mg binary phase diagram and Al–Mg–Zn ternary phase diagram. The network structure was derived from dendritic structure γ-Al₁₂Mg₁₇. Friction pressure could improve the liquid–solid hybrid microstructure morphology at the welding interface.     

Effect of intermetallics on susceptibility of Mg alloy welds to liquation cracking

ABSTRACT

The circular-patch welding test was used to study the liquation and liquation cracking of AZ-series Mg alloys. A heat treatment was carried out on the as-received AZ91 alloy to dissolve the γ(Mg₁₇Al₁₂) particles before welding. The circular-patch welding test was then conducted on the heat-treated, as-received AZ91 alloy using AZ61 and AZ91 filler wires. The results showed that the susceptibility of AZ91 alloy to liquation and liquation cracking was significantly reduced by the dissolution of massive γ(Mg₁₇Al₁₂) particles via a heat treatment before welding as the liquation mechanism was changed. Both constitutional liquation and incipient melting occurred in the partially melted zone of the as-received AZ91 welds, while only incipient melting occurred in the heat-treated AZ91 welds.     

Effect of alloying elements of steel wire on the structure and properties of coatings in electric arc spraying

This paper reports the results of a comparison between the mechanical characteristics of butt joints in 3.0 mm thick Ti6Al4V titanium alloy sheets, made by laser welding with no filler material and by laser–arc hybrid welding. Vickers hardness tests have been performed on cross-sections of the beads obtained. In particular, the influence of the gap between the sheets in test welds performed using CO₂ laser–MIG hybrid welding has been analysed. Cross-sections of the weld beads obtained with several different gap sizes have been analysed morphologically. The welded joints have been subjected to draw testing, and joint deformation behaviour has been analysed using an optical deformation measurement system based on stereoscopic image capture (ARAMIS 3D analysis system).     

ZGMn13钢HAZ液化裂纹的研究

本文通过几种焊接方法的工艺因素试验,用热塑性试验和焊接热模拟试验等方法,用光镜、电镜、能谱、电子探针等显微分析手段,探讨了ZGMn13钢焊接热影响区(HAZ)裂纹的性质、形成机理和影响因素。结果表明:ZGMn13钢HAZ 裂纹为液化裂纹及其扩展的结果。这种液化裂纹主要是由于P、S 等杂质元素所形成的低熔点相、非金属夹杂物和碳化物导致晶界液化或弱化,在较大的焊接应力作用下形成的。采用小线能是CO_2气体保护焊能明显减少ZGMn13钢HAZ 的液化裂纹倾向。     

经济型铁素体不锈钢焊接接头组织与耐蚀性能

采用ER-309焊丝焊接了TCS345,T4003,Nirosta 4003,JFE410RW四种铁素体不锈钢,用金相方法分析了四种母材、接头的显微组织,通过电化学极化曲线测量,对母材和焊接接头的耐腐蚀性能进行了评价.结果表明,TCS345和T4003铁素体不锈钢与Nirosta 4003和JFE410RW铁素体不锈钢的主要区别是钛和锰含量偏低,尤其是钛含量少,导致TCS345和T4003铁素体不锈钢的晶粒长大倾向较Nirosta 4003和JFE410RW铁素体不锈钢的明显.铁素体不锈钢焊接接头存在较大的热影响区,热影响区的组织与母材晶粒相比,其晶粒明显粗大;TCS345铁素体不锈钢的晶粒长大严重,Nirosta 4003和JFE410RW铁素体不锈钢的铁素体晶粒尺寸比TCS345略小,晶粒长大不明显.在1mol/L Na2SO4溶液中,TCS345和JFE410RW不锈钢母材的腐蚀性能优于T4003和Nirosta 4003.     

Si含量对Al-Mn-Mg合金激光焊接性能的影响

研究Al-Mn-Mg铝合金板材的Si含量（0．1％～0．5％,质量分数）对其脉冲激光焊接性能的影响。试验材料为实验室制备的0．45mm厚的H16态板材。激光焊接试验后发现,当Si含量低于0．34％时,焊池里没有产生裂纹;但是,当Si含量增加到0．47％时,焊池里有裂纹产生。微观组织观察表明,当Si含量低的时候,晶界上残留的共晶相呈不连续的点状分布：当Si含量高的时候,晶界上残留的共晶相变成连续分布。这种现象可以解释增加Si含量对激光焊接性能产生的不利影响。     

表面纳米化对镍基高温合金焊接液化裂纹的影响

采用搅拌摩擦处理对Waspaloy高温合金进行表面纳米化，并用激光对搅拌区域进行重熔，研究表面纳米化对液化裂纹的影响. 利用扫描电镜和电子背散射衍射，研究了搅拌区域和重熔区域的显微组织. 结果表明，搅拌摩擦处理在Waspaloy合金表面制备出200 ~ 700 nm的等轴纳米晶粒，细化机制为不连续动态再结晶；从搅拌区表层至底部，晶粒尺寸整体上逐渐增大；经激光重熔后，发现纳米晶层有效抑制了热影响区液化裂纹. 纳米化过程改变了碳化物的分布，避免液化相富集于晶界，晶粒尺寸减小则使晶界面积大大增加，从而减小了液膜厚度，抑制了裂纹的形成.     

Effect of modified AA4043 filler on partially melted zone cracking of Al-alloy gas tungsten arc welds

Abstract

The effect of grain refiners (zirconium, Tibor and scandium) added to the fusion zone through AA4043 filler on the partially melted zone (PMZ) cracking in gas tungsten arc (GTA) welded AA6061 alloy was investigated. Welds of AA6061 in thermal tempers of artificially aged condition (T6) were made with continuous current and pulsed current techniques. Varestraint testing was carried out to study PMZ cracking in welds, and optical SEM examination performed to evaluate it. Addition of grain refiners to the fusion zone improved the PMZ cracking resistance very significantly. Pulsed current technique was also found to improve the resistance to PMZ cracking, as a result of the possible reduction in the strain in the PMZ owing to the ductile fine grained fusion zone. Severe PMZ cracking in the welds of AA4043 filler without grain refiners was attributed to a greater amount of silicon rich eutectic at the grain boundaries of the PMZ.     

Laser surface treatment and its influence on the development of healing Cr2O3 scales on nickel-chromium alloys

The influence of laser surface treatment on the isothermal oxidation of Ni-10%Cr and Ni-15%Cr at 1025°C in oxygen at 1 atm pressure has been studied. Particular emphasis has been placed on the progressive establishment of a Cr₂O₃ healing layer, which is facilitated by rapid-diffusion paths for chromium to the surface from the bulk alloy. For nonlaser treated alloys, such paths are alloy grain boundaries. A partial Cr₂O₃ layer forms initially in localized sites at, and immediately adjacent to, these boundaries and progresses into the alloy grains in a stepwise manner following lateral diffusion of chromium from the grain boundaries, thereby developing a contoured configuration. For Ni-15%Cr, there is sufficient chromium in the bulk alloy grains to sustain the eventual development of a self-healing layer parallel to the surface. For Ni-10%Cr, this is not the case and complete development of the healing layer results entirely from the stepwise progression from the grain boundaries. Establishment of the healing layer on laser-glazed surfaces is facilitated by additional rapid-diffusion paths, particularly retained alloy grain boundaries, retained alloy twins, a laser-induced microstructure and solidification artifacts (such as ripples). The relative importance of these features is discussed in relation to the oxidation behavior.     

Structure and nanomechanical characteristics of Al–Cu–Mg–Si alloy with partly liquated grain boundaries upon heat treatment

The microstructure, phase composition, and mechanical characteristics of the structural constituents of an Al–Cu–Mg–Si alloy in which the liquation of grain boundaries occurred during heat treatment have been studied. Bands of the (Al + Al₁₅(Fe, Mn)₃Si₂) eutectics have been observed at the grain boundaries. An algorithm for calculating the additional pressure, which results from mechanical impact on the metal containing these bands has been described.     

ZK40高强镁合金CO2激光焊接接头的组织与力学性能

采用C2激光对轧制态ZK40镁合金板材进行焊接,并研究焊接工艺参数对接头显微组织及力学性能的影响规律.结果表明:在合理的工艺条件下,可以获得成型良好的焊接接头,其抗拉强度可达到315MPa,为母材的91.3%;熔池边界无外延生长的柱状晶,整个熔池完全由细小均匀的等轴树枝晶组成:分布于晶界及枝晶臂间的第二相粒子主要是Mg<,51>Zn<,20>;随着焊接热输入的增大,枝晶臂生长更为发达,晶粒粗化.