Microstructure and mechanical properties of dissimilar friction stir welding of 6061-to-7050 aluminum alloys

In this work, the microstructure and mechanical properties of friction stir welded dissimilar butt joints of 6061-to-7050 aluminum alloys were evaluated. Microstructure analysis of the cross-section of the joints revealed distinct lamellar bands and various degrees of intermixing that were correlated with tool rotational speed. Due to the distinct mechanical properties of the two alloys, microhardness measurements showed a consistent asymmetric hardness distribution profile across the weld nugget, regardless of tool rotational speed. Under monotonic tensile loading, an increase in the joint strength was observed with the increase in the tool rotational speed. Regarding fracture, the joints consistently failed on the 6061 aluminum alloy side. Furthermore, two modes of failure were observed, one through the stir zone and the other through the heat-affected zone. Inspection of the fracture surfaces suggested that inadequate material intermixing produced at low tool rotational speeds was the cause for the low mechanical strength and failure through the stir zone. On the other hand, the failure observed through the heat-affected zone at high rotational speeds was produced due to the material softening as confirmed by the microhardness measurements.     

Welding and Joining of NiTi Shape Memory Alloys: A Review

NiTi is an increasingly applied material in industrial applications. However, the difficulties faced when welding and joining is required, limits its broader use in the production of complex shaped components. The main weldability problems associated with NiTi are: strength reduction, formation of intermetallic compounds, modification of phase transformation and transformation temperatures, as well as, changes in both superelastic and shape memory effects. Additionally, NiTi is envisaged to be joined to other materials, in dissimilar joints with more complex problems depending on the other base material. Thus, intensive research in welding and its effects on the joints performance has been conducted since the early stages of NiTi. This paper presents a detailed review of welding and joining processes applied to NiTi, in similar and dissimilar combinations considering both fusion and solid-state processes. Since laser is the most studied and applied welding process, a special section is devoted to this technique.     

TP304H与12Cr1MoV锅炉管异种钢的焊接

利用舍夫勒组织图对韶关发电厂SA2 13TP30 4H与 12Cr1MoV异种钢接头可能出现的焊接组织进行了分析 ,制订出了合理的焊接工艺 ,并对锅炉上的SA2 13TP30 4H与 12Cr1MoV钢焊口进行了施焊 ,经 17个月的运行 ,10 4个焊口未出现爆漏现象     

Hot Corrosion Behavior of Friction Welded AISI 4140 and AISI 304 in K2SO-60% NaCl Mixture

Understanding the behavior of weldment at elevated temperatures and especially the corrosion behavior has become an object of scientific investigation recently.Investigation has been carried out on friction welded AISI 4140 and AISI 304 in molten salt of K 2 SO 4-60% NaCl environment at 550,600 and 650 C under cyclic condition.The resulted oxide scales in the weldment have been characterized systematically by surface analytical techniques.From the results of the experiments,it is observed that the scale thickness on low alloy steel side was higher than that on stainless steel side.Furthermore,weld interface has been found to be more susceptible to degradation than base metals due to inter diffusion of element across the interface and the formation of intermetallic compound.The influences of welding parameters and the temperature of exposure on the hot corrosion behavior of the weldment were discussed in this paper.     

不清根手工双面焊材料及工艺研究

本文分析了中厚板传统手工双面焊存在的诸如打底焊焊缝质量无法保证，需用碳弧气刨清根；工人劳动强度大；生产效率低；焊接质量不稳定等主要问题。为提高打底焊焊道质量，不用清根使背面得到良好的凹成形，研制了适合Ｘ形坡口的梯形体陶瓷衬垫。探讨了焊缝背面成形的主要影响因素及控制方法。     

Single pass laser joining of Inconel 718 superalloy with filler

Abstract

Microstructure and mechanical property of CO₂ laser beam welded IN 718 superalloy were studied by electron microscopy and hardness testing. The use of a welding filler wire produced a sound fusion zone with no cracking but grain boundary microfissuring occurred in the heat affected zone (HAZ) and was observed to be significantly influenced by pre-weld heat treatment and laser welding speed. Crack-free weld was produced by a pre-weld heat treatment that minimised non-equilibirum grain boundary boron segregation and inhibited grain growth. While post-weld heat treatment (PWHT) reduced the difference between the hardness values of the base alloy, HAZ and the fusion zone, it resulted in increased HAZ cracking, which was likely aided by pre-existing cracks. The PWHT cracking was, however, avoided by subjecting pre-weld material to the heat treatment condition that produces crack-free weld during welding process.     

Dissimilar welding of WC–Co cemented carbide to Ni42Fe50.9C0.6Mn3.5Nb3 invar alloy by laser–tungsten inert gas hybrid welding

Dissimilar welding between cemented carbide and invar alloy was carried out using CO₂ laser beam and argon arc as heat sources. η Phase was formed near WC–Co/weld interface and precipitations in the fracture were discovered. In order to disclose the microstructure and mechanical property, firstly, η phase’s morphology and composition at interface were investigated using backscattered electron imaging (BEI); and element diffusion across heat affected zone near WC–Co/weld interface was further studied. Secondly, bend strength values of butt joint with different welding parameters were tested by four-point bend strength experiment. Finally, WC migration mechanism was further discussed and the bend strength was measured. The results showed: (1) microstructures consisted of columnar crystals, cellular crystals, eutectic structure and fir-tree crystal and dendritic crystals. The columnar crystals were surrounded by lots of fir-tree crystals. (2) WC migration was driven by stirring effects of welds, high pressure of molten materials and ionized shielding gas, interface reaction and surface tension. (3) η Phases dispersion did not decrease bend strength of butt joint. And the maximum bend strength was 1493.56 MPa, which was attributed to NbC precipitations featured with super-fine fir-tree.     

连续束焊机焊丝嘴用碳陶瓷复合材料的研究

介绍了连续束焊机焊丝嘴用碳陶瓷复合材料的制备工艺及性能，结果表明，该材料具有较高的抗弯强度、断裂韧性和硬度值，而且还有良好的导电、导热、抗氧化及抗热震性能和减磨耐磨特性。用该材料制备的焊丝嘴，克服了使用原铜合金嘴焊接时的卡丝、咬丝、熔结等现象。焊缝质量稳定，焊丝嘴使用寿命较原铜嘴提高３￣５倍。