Arc Behavior and Droplet Transfer of CWW CO2 Welding

Cable-type welding wire (CWW)CO2 welding is an innovative process arc welding with high quality,high efficiency and energy saving,in which CWW is used as consumable electrode.The CWW is composed of seven wires with a diameter of 1.2 mm.One is in the center,while others uniformly distribute around it.The diameter of twisted wire is up to 3.6 mm,which can increase the deposition rate significantly.With continual wire-feeding and melting of CWW,the formed rotating arc improved welding quality obviously.The arc behavior and droplet transfer were ob-served by the electrical signal waveforms and corresponding synchronous images,based on the high speed digital camera and electrical signal system.The results showed that the shape of welding arc changed from bell arc to beam arc with the increase of welding parameter.The droplet transfer mode changed from repelled transfer,globular transfer to projected transfer in turn.Droplet transfer frequency increased from 18.17 Hz to 119.05 Hz,while the droplet diameter decreased from 1.5 times to 0.3 times of the CWW diameter.     

Microstructure and Properties Analysis of Laser Welding and Laser Weld Bonding Mg to Al Joints

Laser welding and laser weld bonding (LWB) Mg to Al joints were obtained in different welding parameters. The penetrations and microstructures of these kinds of joints changed with the increasing of pulse laser power density. Both laser welding and LWB Mg to Al joints with the best properties were obtained in conductive welding mode. In laser welding Mg to Al joint, several intermetallics formed at the bottom of the fusion zone, where some cracks were generated. In laser weld bonding Mg to Al joint, the decomposition of the adhesive caused a baffle effect on the diffusion between the Mg and the Al. The intermetallics formed in the middle of the fusion zone, and the thickness of Mg₁₇Al₁₂ layer was approximately 10 to 20 μm and the Mg₂Al₃ layer was less than 5 μm, which influenced the property of the joint less.     

Effects of Ultrasonic Vibration on Material Flow and Thermal Cycles in Friction Stir Welding of Dissimilar Al/Mg Alloys

Comparative experiments are performed in friction stir welding (FSW) of dissimilar Al/Mg alloys with and without assistance of ultrasonic vibration. Metallographic characterization of the welds at transverse cross sections reveals that ultrasonic vibration induces differences in plastic material flow in two conditions. In FSW, the plastic material in the peripheral area of shoulder-affected zone (SAZ) tends to flow downward because of the weakening of the driving force of the shoulder, and a plastic material insulation layer is formed at the SAZ edge. When ultrasonic vibration is exerted, the stirred zone is divided into the inner and outer shear layers, the downward material flow trend of the inner shear layer disappears and tends to flow upward, and the onion-ring structure caused by the swirl motion is avoided in the pin-affected zone. By improving the flow behavior of plastic materials in the stirred zone, ultrasonic vibration reduces the heat generation, accelerates the heat dissipation in nugget zone and changes the thermal cycles, thus inhibiting the formation of intermetallic compound layers.

     

Low-Cycle Fatigue Behavior of Die-Cast Mg Alloys AZ91 and AM60

The influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91 and AM60 has been investigated. Fatigue lifetimes were determined from the total strain-controlled fatigue tests for strain amplitudes of 0.2?pct, 0.4?pct, 0.6?pct, 0.8?pct, and 1.0?pct under fully reversed loading at a frequency of 5?Hz. Cyclic stress?Cstrain behavior was determined using an incremental step test (IST) and compared with the more traditional constant amplitude test. Two locations in a prototype casting were investigated to examine the role of microstructure and porosity on fatigue behavior. At all total strain amplitudes microstructure refinement had a negligible impact on fatigue life because of significant levels of porosity. AM60 showed an improvement in fatigue life at higher strain amplitudes when compared with AZ91 because of higher ductility. T6 heat treatment had no impact on fatigue life. Cyclic stress?Cstrain behavior obtained via the incremental step test varied from constant amplitude test results due to load history effects. The constant amplitude test is believed to be the more accurate test method. In general, larger initiation pores led to shorter fatigue life. The fatigue life of AZ91 was more sensitive to initiation pore size and pore location than AM60?at the lowest tested strain amplitude of 0.2?pct. Fatigue crack paths did not favor any specific phase, interdentritic structure or eutectic structure. A multistage fatigue (MSF) model showed good correlation to the experimental strain-life results. The MSF model reinforced the dominant role of inclusion (pore) size on the scatter in fatigue life.     

铝合金激光深熔焊接热过程有限元数值模拟

对铝合金5A06简体纵缝进行激光深熔焊接。建立了该条件下的焊接热源模型,热源模型由沿激光入射方向的旋转高斯体热源构成。使用该热源模型和ANSYS有限元分析软件对前述的试验进行了数值模拟。为制定和优化焊接工艺提供必要的参考。     

连铸辊的明弧焊和埋弧焊工艺及使用效果比较

主要介绍了宽中厚板坯连铸机扇形段辊子采用的两种堆焊工艺一埋弧焊和明弧焊。阐述两种不同堆焊工艺在同一台连铸机上使用后得出的不同的使用效果。     

Process Parametric Dependency of Axial Downward Force and Macro- and Microstructural Morphologies in Ultrasonically Assisted Friction Stir Welding of Al/Mg Alloys

Metallurgical and Materials Transactions A - An elementary analysis is proposed to quantify the effects of ultrasonic vibrations during friction stir welding (FSW) of AA6061-T6 to AZ31B Mg alloy....     

Submerged Friction-Stir Welding (SFSW) Underwater and Under Liquid Nitrogen: An Improved Method to Join Al Alloys to Mg Alloys

Submerged friction-stir welding (SFSW) underwater and under liquid nitrogen is demonstrated as an alternative and improved method for creating fine-grained welds in dissimilar metals. Plates of AZ31 (Mg alloy) and AA5083 H34 were joined by friction-stir welding in three different environments, i.e., in air, water, and liquid nitrogen at 400?rpm and 50?mm/min. The temperature profile, microstructure, scanning electron microscopy (SEM)-energy-dispersive spectroscopy (EDS) analysis, X-ray diffraction (XRD), hardness, and tensile testing results were evaluated. In the stir zone of an air-welded specimen, formation of brittle intermetallic compounds of Al₃Mg₂, Al₁₂Mg₁₇, and Al₂Mg₃ contributed to cracking in the weld nugget. These phases were formed because of constitutional liquation. Friction-stir welding underwater and under liquid nitrogen significantly suppresses the formation of intermetallic compounds because of the lower peak temperature. Furthermore, the temperature profiles plotted during this investigation indicate that the largest amount of ?T is generated by the weld under liquid nitrogen, which is performed at the lowest temperature. It is shown that in low-temperature FSW, the flow stress is higher, plastic contribution increases, and so adiabatic heating, a result of high strain and high strain-rate deformation, drives the recrystallization process beside frictional heat.     

Influence of CO2-Ar Mixtures as Shielding Gas on Laser Welding of Al-Mg Alloys

In this study, AA5083 samples were butt welded under a conduction regime with high-power diode laser (HPDL). Various mixtures composed of Ar and CO₂ were used as a shielding gas. The influence of the shielding gas composition on the microstructure and on the properties of laser welds was analyzed. The weld beads were deeply characterized by metallographic/microstructural studies, X-ray diffraction (XRD), X-ray energy dispersive spectrometry (X-EDS) chemical analyses, X-ray photoelectron spectra (XPS), microhardness, and tensile strength. The corrosion resistance of laser-remelted surfaces with different CO₂/Ar ratios was also estimated by means of electrochemical tests. The addition of CO₂ to the shielding gas results in a better weld penetration and oxidizes the weld pool surface. This addition also promotes the migration of Mg toward the surface of weld beads and induces the formation of magnesium aluminates spinel on the welds. The best corrosion resistance result is achieved with 20 pct CO₂. The overall results indicate that the addition of small percentage of CO₂ to Ar leads to improvements of the mechanical and corrosion properties of the aluminum welds.     

Texture Weakening Effects in Ce-Containing Mg Alloys

The purpose of the present study is to elucidate the cause of a texture transition observed in hot-rolled Mg-Ce alloys, with increasing Ce content. More dilute compositions show a predominance of basal 〈a〉 dislocations, while the more concentrated alloys are shown to contain significant populations of 〈c+a〉 and non-basal 〈a〉 dislocations in the as-rolled and the recovery-annealed conditions. Like Mg-Nd, the grain size in Mg-Ce decreases with increasing Ce. Unlike Mg-Nd, the second-phase particles observed are of the equilibrium phase, and the equilibrium solid solubility at the hot working temperature corresponds to the composition above which weak textures form. The significances of both non-basal slip and Zener pinning as contributors to texture randomization are discussed.     

高氮奥氏体不锈钢熔焊时电弧空间及熔池的氦行为

高氮奥氏体不锈钢是利用氮代替镍进行合金化的一种合金结构钢，氮的固溶存在是材料具备优良性能的前提。焊接是高氮奥氏体不锈钢工程应用需要解决的首要问题之一，氮是影响其焊接性的主要因素，为了获得与母材性能匹配的焊接接头，必须理解熔焊过程中的氮行为。对熔焊时电弧区、熔池区的氮行为进行了分析，以实现焊缝固溶氮含量的有效控制。     

高氮奥氏体不锈钢熔焊时电弧空间及熔池的氮行为

 高氮奥氏体不锈钢是利用氮代替镍进行合金化的一种合金结构钢,氮的固溶存在是材料具备优良性能的前提。焊接是高氮奥氏体不锈钢工程应用需要解决的首要问题之一,氮是影响其焊接性的主要因素,为了获得与母材性能匹配的焊接接头,必须理解熔焊过程中的氮行为。对熔焊时电弧区、熔池区的氮行为进行了分析,以实现焊缝固溶氮含量的有效控制。     

Wear Behavior of Aluminum Matrix Hybrid Composites Fabricated through Friction Stir Welding Process

Effects of friction stir processing (FSP)parameters and reinforcements on the wear behavior of 6061-T6 based hybrid composites were investigated.A mathematical formulation was derived to calculate the wear volume loss of the composites.The experimental results were contrasted with the results of the proposed model.The influ-ences of sliding distance,tool traverse and rotational speeds,as well as graphite (Gr)and titanium carbide (TiC) volume fractions on the wear volume loss of the composites were also investigated using the prepared formulation. The results demonstrated that the wear volume loss of the composites significantly increased with increasing sliding distance,tool traverse speed,and rotational speed;while the wear volume loss decreased with increasing volume fraction of the reinforcements.A minimum wear volume loss for the hybrid composites with complex reinforcements was specified at the inclusion ratio of 50% TiC+50% Al2 O3 because of improved lubricant ability,as well as resist-ance to brittleness and wear.New possibilities to develop wear-resistant aluminum-based composites for different in-dustrial applications were proposed.     

Irradiation Behavior in High Entropy Alloys

As an increasing demand of advanced nuclear fission reactors and fusion facilities,the key requirements for the materials used in advanced nuclear systems should encompass superior high temperature property,good behavior in corrosive environment,and high irradiation resistance,etc.Recently,it was found that some selected high entropy alloys(HEAs) possess excellent mechanical properties at high temperature,high corrosion resistance,and no grain coarsening and self-healing ability under irradiation,especially,the exceptional structural stability and lower irradiation-induced volume swelling,compared with other conventional materials.Thus,HEAs have been considered as the potential nuclear materials used for future fission or fusion reactors,which are designed to operate at higher temperatures and higher radiation doses up to several hundreds of displacement per atom(dpa).An insight into the irradiation behavior of HEAs was given,including fundamental researches to investigate the irradiation-induced phase crystal structure change and volume swelling in HEAs.In summary,a brief overview of the irradiation behavior in HEAs was made and the irradiation-induced structural change in HEAs may be relatively insensitive because of their special structures.     

Multi-objective Optimization of Welding Parameters in Submerged Arc Welding of API X65 Steel Plates

Submerged arc welding(SAW)is one of the main welding processes with high deposition rate and high welding quality.This welding method is extensively used in welding large-diameter gas transmission pipelines and high-pressure vessels.In welding of such structures,the selection process parameters has great influence on the weld bead geometry and consequently affects the weld quality.Based on Fuzzy logic and NSGA-II(Non-dominated Sorting Genetic Algorithm-II)algorithm,a new approach was proposed for weld bead geometry prediction and for process parameters optimization.First,different welding parameters including welding voltage,current and speed were set to perform SAW under different conditions on API X65 steel plates.Next,the designed Fuzzy model was used for predicting the weld bead geometry and modeling of the process.The obtained mean percentage error of penetration depth,weld bead width and height from the proposed Fuzzy model was 6.06%,6.40% and 5.82%,respectively.The process parameters were then optimized to achieve the desired values of convexity and penetration indexes simultaneously using NSGA-II algorithm.As a result,a set of optimum vectors(each vector contains current,voltage and speed within their selected experimental domains)was presented for desirable values of convexity and penetration indexes in the ranges of(0.106,0.168)and(0.354,0.561)respectively,which was more applicable in real conditions.     

Friction Stir Welding of Dissimilar Al/Al and Al/Non-Al Alloys: A Review

Metallurgical and Materials Transactions B - Friction stir welding is a solid-state welding technique that has many advantages over traditional fusion welding, and has been widely adopted in the...     

The Nature of Native MgO in Mg and Its Alloys

Metallurgical and Materials Transactions A - Native MgO particles in Mg-alloy melts have been recently exploited as potential substrates for heterogeneous nucleation during solidification, leading...