不锈钢与耐候钢MIG电弧钎焊工艺

采用手工MIG电弧钎焊工艺对SUS304不锈钢与Q355GNHD耐候钢薄板对接接头进行工艺试验,按照相关技术标准进行焊接工艺评定。结果表明,MIG电弧钎焊工艺能够成功用于SUS304不锈钢和Q355GNHD耐候钢薄板对接接头的钎焊,焊缝成形质量良好,经X射线探伤无缺陷;接头的抗拉强度平均值为339.58 MPa,接头强度系数为78.97%。采用光学显微镜观察SUS304不锈钢与铜基钎料间产生的渗透裂纹,讨论渗透裂纹的产生机理。     

Microstructure Evolution During Stainless Steel-Copper Vacuum Brazing with a Ag/Cu/Pd Filler Alloy: Effect of Nickel Plating

Vacuum brazing of stainless steel and copper plates was done using a silver-based filler alloy. In one set of experiments, around 30-µm-thick nickel coatings were electrochemically applied on stainless steel plates before carrying out the brazing runs and its effect in making changes in the braze-zone microstructure was studied. For brazing temperature of 830 °C, scanning electron microscopy examination of the braze-zone revealed that relatively sound joints were obtained when brazing was done with nickel-coated stainless steel than with uncoated one. However, when brazing of nickel-coated stainless steel and copper plates was done at 860 °C, a wide crack appeared in the braze-zone adjacent to copper side. Energy-dispersive x-ray analysis and electron microprobe analysis confirmed that at higher temperature, the diffusion of Cu atoms from copper plate towards the braze-zone was faster than that of Ni atoms from nickel coating. Helium leak rate of the order 10^?11 Pa m³/s was obtained for the crack-free joint, whereas this value was higher than 10^?4 Pa m³/s for the joint having crack. The shear strength of the joint was found to decrease considerably due to the presence of crack.     

Zinc corrosion runoff process induced by humid tropical climate

Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 – 8.5 ± 0.30 g Zn m^?2yr^?1) were released, being the runoff 63 – 87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO₂ as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel     

The anaerobic corrosion of candidate disposal canister materials in compacted bentonite exposed to natural granitic porewater containing native microbial populations

The materials corrosion test (MaCoTe) is a long-term, multinational in situ corrosion experiment setup at the Grimsel Test Site, Switzerland. The experiment has been operating since 2014 with a focus on the corrosion behaviour of container materials for the disposal of high-level waste and spent nuclear fuel under conditions representing a granitic deep geological repository. The experiment consists of eight modules containing metal coupons and bentonite. Two of the modules, each with a different bentonite density, have been retrieved after 394 days of exposure and have been analysed using a range of techniques aimed at studying the corrosion behaviour of the metals and the mineralogical evolution of the bentonite. Weight loss measurements show that carbon steel had a relatively low average corrosion rate (~2 µm year⁻¹). Much lower average corrosion rates were measured for the various types of copper (0.13–0.32 µm year⁻¹). No detectable corrosion was measured on stainless steel coupons. To date, no significant differences were observed in the corrosion behaviour and rate of the test metals in bentonite with different dry densities.     

Gas metal arc brazing of galvannealed steel sheets

An advanced gas metal arc welding technique with controlled short-circuiting mode of metal transfer and arcing at low power was employed for brazing of galvannealed steels using CuSi3 filler wire. The brazed joints showed the presence of an interface layer with Fe–Si intermetallic compounds (IMC). Increase in heat input resulted in an increase of the interface layer thickness. The maximum failure load of 2.5?kN was achieved for a heat input of 105?J?mm^?1 with the corresponding interface layer thickness of 2.7?µm. Heat inputs beyond 105?J?mm^?1 led to excessive spatter of zinc and increase in interface layer thickness with hard Si-rich IMC. In contrast, heat input values lower than 80?J?mm^?1 produced inadequate wetting of the steel surface by the molten filler wire deposit and resulted in low joint strength.     

Untersuchung der Spannungsrißkorrosion von Baustählen in flüssigem Zink

Investigation into stress corrosion cracking of unalloyed steels in liquid zinc This investigation has been done in order to get further informations of stress corrosion cracking in galvanized steel. The samples were made of unalloyed steel with increased contents of carbon (up to 0,24%), silicon (up to 0,30%) and copper (up to 0,4%). Welded and notched samples have been equally tested. One batch of the samples was preloaded with 70, 80, 90 and 100% of yield point and then dipped into hot zinc (450°C). Another batch was tested in liquid zinc with constant strain rates of 5 · 10^?4, 5 · 10^?5, and 5 · 10^?6 · s^?1 during 250 h. None of the tested samples have been destroyed by stress corrosion cracking.     

Long-term corrosion behaviour of carbon steel and stainless steel in Opalinus clay: influence of stepwise temperature increase

ABSTRACT

Carbon steel (C-steel; E24 and S235 grades) and stainless steel (316L) electrodes were corroded in situ in Opalinus clay under anoxic conditions in a vertical descending borehole. The electrodes were exposed at ambient temperature for two years, and then at 85°C for five years. In situ electrochemical impedance spectroscopy showed that the instantaneous corrosion rate of C-steel decreased over time down to 1?µm?year^?1, followed by steady state. Microbial and chemical investigations showed that sulphate and thiosulphate reducing prokaryotes were present in the porewater and at the metal surface. Post mortem characterisation revealed contrasting corrosion aspects. The E24 corrosion interface was thick and contained magnetite, mackinawite, hydroxychloride and siderite, together with more oxidised species (goethite, greigite, elemental sulphur). The S235 corrosion interface was thinner and contained siderite and mackinawite. Corrosion damage of the 316L electrode was negligible, and the surface was covered by a thin fringe of pyrite.     

Evaluation of Corrosion Performance of Titanium/Steel Joint Brazed by Cu-Based Filler Metal

Furnace vacuum brazing has been employed to join commercially pure titanium and low carbon steel using copper-based filler metal with the composition of Cu-10.6Mn-1.9Ni, at.%. Three different brazing temperatures 930, 970, and 1000 °C and a holding time of 15 min were studied and evaluated. The corrosion behavior of the joint in 0.1 M sulfuric acid was investigated using immersion and electrochemical tests. Measurements of corrosion potential, corrosion current density, corrosion rate, polarization resistance, weight loss, and morphology of corrosion attack were used in this study. Experimental results showed that severe corrosion attack of the steel side at the interfacial area is clearly observed. Despite the difference in corrosion rate values obtained by electrochemical and weight loss measurements, the trend of results was identical to a large extent. Corrosion resistance of the joint showed a general tendency to increase with rising brazing temperature. The lowest corrosion rate was obtained for the couple bonded at 1000 °C. Meanwhile, at the lowest joining temperature of 930 °C, corrosion rate showed a higher value. The results of joints corrosion resistance were attributed to the difference in microstructure features and chemical analysis.     

Preliminary Investigation of the Corrosion Behavior of Proprietary Micro-alloyed Steels in Aerated and Deaerated Brine Solutions

The corrosion performance of fairly new generation of micro-alloyed steels was compared in different concentrations of aerated and deaerated brines. Electrochemical polarization, weight loss and surface analyses techniques were employed. The results showed a threshold of corrosion rate at 3.5 wt.% NaCl in both aerated and deaerated solutions. The average corrosion current density for steel B, for example, increased from 1.3 µA cm^?2 in 1 wt.% NaCl to 1.5 µA cm^?2 in 3.5 wt.% NaCl, but decreased to 1.4 µA cm^?2 in 10 wt.% deaerated NaCl solutions. The aerated solutions exhibited an average of over 80% increase in corrosion current density in the respective concentrations when compared with the deaerated solution. These results can be attributed to the effects of dissolved oxygen (DO) which has a maximum solubility in 3.5 wt.% NaCl. DO as a depolarizer and electron acceptor in cathodic reactions accelerates anodic metal dissolution. The difference in carbon content and microstructures occasioned by thermo-mechanical treatment contributed to the witnessed variation in corrosion performance of the steels. Specifically, the results of the various corrosion techniques corroborated each other and showed that the corrosion rate of the micro-alloyed steels can be ranked as CR_{Steel A} < CR_X65 < CR_{Steel B} < CR_{Steel C}.     

Electrochemical Corrosion Behavior of Thermal-Sprayed Stainless Steel-Coated Q235 Steel in Simulated Soil Solutions

The corrosion behavior of a thermal-sprayed stainless steel (SS)-coated Q235 steel has been investigated in simulated soil solutions using electrochemical measurements, x-ray photoelectron spectroscopy analysis, and scanning electron microscope. The as-received Q235 steel and galvanized steel for grounding grids were also examined for the purpose of comparison. The effects of pH value of testing solutions have been examined. The thermal-sprayed SS-coated steel showed the best corrosion resistance among the three kinds of materials. With increasing pH value, the corrosion resistance of SS-coated Q235 steel increased. In weak alkaline solutions, the SS-coated Q235 steel showed the largest polarization resistance (3.2 × 10⁵ Ω cm²), the lowest anodic current density (1.4 × 10^?2 μA/cm²), and the largest film resistance (4.5 × 10⁶ Ω cm²), suggesting that the coated steel has the best corrosion resistance in weak alkaline environment. Related corrosion mechanisms are also discussed.     

Fluxless laser brazing of aluminium alloy to galvanized steel using a tandem beam – dissimilar laser brazing of aluminium alloy and steels

Tandem beam brazing with aluminium filler metal (BA4047) was conducted in order to develop the fluxless laser brazing technique of aluminium alloy (AA6022) to galvanized steels (GA and GI steels). Laser powers of tandem beam and offset distance of preheating beam from the root to the steel base metal were varied. Sound braze beads could be obtained by optimizing the preheating and main beam powers under the offset distances of 0–1 mm. A small amount of zinc remained at the braze interface between galvanized steels and the braze metal. The reaction layer consisting of Fe–Al intermetallic compounds was also formed at the steel interface, and the thickness of reaction layer could be predicted during the laser brazing (thermal cycle) process based on the growth kinetics with the additivity rule. The metal flow analysis of the melted filler metal on joints revealed that wettability and spreadability of the filler metal on the GI steel joint were superior to those on the GA steel joint. The fracture strength of the lap joint attained approx. 55–75% of the base metal strength of aluminium alloy. It was concluded that fluxless laser brazing could be successfully performed by using a tandem beam because the zinc coat layer acted as the brazing flux.     

Cold metal transfer welding–brazing of magnesium to pure copper

Magnesium alloy AZ31B and pure copper T2 were lapped and joined by cold metal transfer (CMT) welding–brazing method by AZ61A magnesium alloy wire with a 1·2 mm diameter. Results indicated that a satisfied Mg/Cu CMT welding–brazing joint was obtained in the stable welding processes with no spatter. The joint was composed of Mg–Mg welding joint formed between the Mg weld metal and the Mg base metal, and Mg–Cu brazing joint formed between the Mg weld metal and the local molten Cu base metal. The microstructure and the intermetallic compound (IMC) distribution were inspected and analysed in detail. The interfacial reaction layers of the brazing joint consisted of Mg₂Cu, Al₆Cu₄Mg₅, MgCu₂ and Mg₁₇Al₁₂ IMCs. The tensile shear strength of the Mg/Cu CMT welding–brazing joint could reach 172·5 N mm^?1. In addition, two different fracture modes were observed: at the fusion zone and at the brazing interface.     

辅助TIG电弧对铝合金/不锈钢MIG熔-钎焊接头形成机制及显微组织的影响

利用一种新型的复合熔-钎焊工艺焊接铝合金和不锈钢。在MIG熔-钎焊工艺中,因钢的导热性差而导致焊缝钢侧的温度梯度变化剧烈,利用TIG电弧加热钢侧可改善这一现象。TIG辅助电弧改善了熔融金属在钢基体上的润湿性,使熔融金属能充分地在钢侧焊接坡口区正面及背面充分润湿,所得接头成形良好;增加了金属间化合物层内Cr、Ni的含量,提高了其力学性能;同时,改变了化合物层的形貌,增强了其与焊缝的结合强度。TIG辅助焊接工艺下获得接头的平均拉伸强度（146.7 MPa）明显高于无辅助TIG电弧下接头的拉伸强度（96.7 MPa）。     

Potential of biocorrosion in Danish district heatings sytems

Danish district heating (DH) systems utilise water with unique characteristics that include low conductivity, high pH, nutrient poor and anaerobic (oxygen free) conditions in order to reduce corrosion rates. This survey was carried out in order to investigate the potential for biofilm formation and biocorrosion in these systems. Determination of total bacterial numbers in water samples were performed in 29 DH systems and showed a range of 10²–10⁵ cells · ml^?1. The potential for biofilm growth was further examined in corrosion monitoring units located at 6 DH locations. Total bacterial numbers in biofilm on mild steel were found in the range of 10⁴–10⁶ cells · cm^?2. The mild steel coupons were examined for general corrosion rates based on weight loss together with an investigation of pitting corrosion. The general corrosion rates were up to 12 μm · year^?1, while the pitting analysis showed pit depths up to 90 μm for half a year of exposure. Presence of sulphate reducing bacteria (SRB) was found in all systems tested with corrosion monitoring units, whereas sulphide was found to different extents in the biofilms on all mild steel coupons. It was shown that DH systems with the highest number of bacteria in the biofilm generally had the most pronounced corrosion. The results show that despite the nutrient poor environment in the DH systems the potential for biofilm formation and biocorrosion was present.     

Development of High Speed Lead Plating and its Applications

A high speed lead plating process has been developed. The bath contains, per gal US, Pb(BF₄)₂ 62·5 oz, HBF₄ and H₂BO₂ ach 6 oz and hydroquinone 1·3 oz. The optimum temperature is 160°F and cathode surface velocities of 0–150 ft/min have been evaluated. Limiting current densities up to 3100 A/ft² and average operating current densities up to 1000 A/ft² are possible. Deposits are fine grained and cover basis metal defects even with coatings 0·1 mil or less. Brushing the basis metal and especially interrupting the lead deposition to brush the deposit reduces porosity. Coatings 0·05 to 0·1 mil thick so produced on steel when tested resisted corrosion by shellac better than terne and tinplate and were satisfactory in water-base paints. However, lead coatings on steel have poor solderability. Salt spray tests confirm the superiority of the deposits produced from the hydroquinone bath with or without brushing treatments. Copper and tin strikes were of no value in corrosion or solderability tests. Power and metal cost is lower for the lead coatings than for zinc coatings of equal thickness. Production facilities for lead-plating steel strip of various gauges are discussed.     

镀锌板单旁路耦合电弧GMAW高速焊接方法

为了解决镀锌板上锌层易受热烧损,无法使用大电流MIG焊接方法进行高速焊接的问题,采用了一种低热输入高效率的焊接方法——单旁路耦合电弧GMAW(DE-GMAW)用于镀锌板的焊接。搭建了该焊接方法的试验平台,对镀锌板堆焊和搭接接头的高速焊接方法进行试验研究。结果表明,通过调整旁路电流值,单旁路耦合电弧GMAW方法降低了镀锌板上的焊接热输入,并可以在大电流和高焊速的条件下实现镀锌板堆焊和搭接接头的焊接,所得焊缝成形良好,母材变形小,焊接过程稳定无飞溅。焊后镀锌层的烧损与同等热输入条件下的普通MIG焊相比明显降低,保证了镀锌板焊后的耐腐蚀性能。     

MIG welding of S235JR steel with the addition of gaseous sulphur hexafluoride SF6 to argon

The results of investigations of MIG welding of S235JR steel with G4Si1 wire with the addition of gaseous sulphur hexafluoride SF₆ in the concentration of 1.6–6.4% to argon are presented. The aim of the investigations is to investigate the effect of sulphur hexafluoride SF6 on the parameters of droplet metal transfer and the formation of the welded joint in automatic MIG welding in argon.     

Complete Oxidation of Zinc Powder. Validation of Kinetics Models

The kinetics of complete oxidation of different samples of zinc powder by air has been investigated by thermogravimetric measurements under isothermal conditions in the range 973–1,173 K. Particles size was in the 63–80 μm range. We succeeded in carrying out the full oxidation of the powders far above the zinc-metal melting point (692.6 K). This phenomenon is linked to the presence of a thin ZnO layer which confines the liquid metal during the oxidation process. Two kinetics models have been verified. The apparent activation energies obtained from the Arrhenius law were 128 kJ mol^?1 and 129 kJ mol^?1, respectively.     

Brazing of A5056 aluminium alloy with the aid of ultrasonic vibration using Ag filler metal

In order to produce a high strength brazed joint of A5056 aluminium alloy containing magnesium of about 5 mass%, the authors applied a flux-free brazing method with the aid of ultrasonic vibration to the aluminium alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows.

At a brazing temperature of 570°C, just above the eutectic point of Al–Ag binary system, application of ultrasonic vibration for 4.0 s provided the brazed joint with the maximum tensile strength and the strength decreased with the application time. When the brazing temperature was varied from 550 to 580°C and the application time of ultrasonic vibration was kept constant at 4.0 s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminium alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along the (Al₃Mg₂ + Al solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al₃Mg₂ + Al solid solution) phase increased with the ultrasonic application time and the brazing temperature. It seemed that the increase of the hard (Al₃Mg₂ + Al solid solution) phase mainly caused the brazed joint strength to decrease.     

Korrosionsverhalten feuerverzinkter Baustähle in überwiegend sandhaltigen Böden

Corrosion behaviour of galvanized steel in mainly sandy grounds In mainly sandy grounds with different portions of fine parts < 0,06 mm (2,5–20,4%) specimens of ungalvanized and galvanized steel were stored outside and in the laboratory. Besides the composition of the ground, the salinity and the temperature of the ground were varied too. The corrosion rate and, for ungalvanized specimens, the behaviour to pitting corrosion were determined. Furthermore the factors characterising the corrosion behaviour such as specific resistance of soil and corrosion potential were investigated continuously. The loss in weight of metal was much greater for ungalvanized than for galvanized specimens and increased for ungalvanized specimens with an increasing portion of fine parts in the ground. Additions of salt at the beginning of the tests produced an increased amount of metal wastage, but for galvanized specimens they only had an influence upon initial corrosion. The increased removals of material started since contents of 3 · 10^?3 MolCl^? + SO/kg. If salts were added to the ground after 2 years (after the formation of a surface layer), they increased the wastage of material for ungalvanized but not for galvanized specimens. Apart from ungalvanized bars in the soil with a fineness portion of 20,4%, corrosion, after an acceleration at the beginning, slowed down owing to the formation of a surface layer. Ungalvanized specimens were attacked by a strong pitting corrosion and that more in aerated than in dense and, thus, water-containing grounds. The additions of salt accelerate more an uniform corrosion of material than a pitting corrosion. As for galvanized specimens after a local removal of zinc under extreme conditions the steel base had been hardly corroded away. The parts free of zinc were protected cathodically by the still existing zinc. The corrosion of steel depends upon the temperature: by increasing the temperature from 4 to 20°C increases of corrosion up to 100% were stated. As for galvanized surfaces temperature has only a small influence upon corrosion.