Effect of welding parameters on the heat affected zone and the mechanical properties of friction stir welded poly(ethylene-terephthalate-glycol)

The bond strength and the heat affected zone (HAZ) of friction stir welded seams made of poly(ethylene-terephthalate-glycol) are analyzed in the article. The seams were prepared with various settings (rotation speed and feeding rate) and with various welding tools. Using the welding parameters (rotation speed, the feed rate, and the tool diameter) a K-factor characterizing the welding process was defined. The novel K factor is related to the welding heat input, which is in direct correlation with both the range of the HAZ and the mechanical properties of the seam. The HAZ formed was analyzed by stress optical method, the mechanical properties by flexural test. It has been demonstrated that the efficiency factor of the welded joint is closely related to the width of the HAZ and it depends on the welding parameters and the tools. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The influence of thermal distribution on macro profile and dendrites morphology based on temperature field simulation of 6061 aluminum alloy laser welded joint

Abstract

Temperature distribution has an important influence on grain morphology during laser welding process. In this investigation, a three-dimensional finite element model considering the effect of different laser welding parameters on heat distribution was established. Moreover, the macro profile and grain morphology in different regions of 6061 aluminum alloy laser welded joints were studied considering different welding heat input. It was found that the upper and bottom weld widths increase with the welding heat input. As the welding speed and laser power increase, the high temperature regions during welding process are elongated in the welding direction. Besides, the size of coarse equiaxed dendrites in the center of weld seam increase with welding heat input and cooling rate. The thermal field simulation results shows that the different temperature distribution and temperature gradient in different regions of weld seam have great effect on grain morphology. Besides, the temperature gradient is smallest in the center of molten pool, while biggest at the edge of molten pool.     

纤维增强树脂基复合材料的搅拌摩擦焊研究

利用搅拌摩擦焊实现了纤维增强树脂基复合材料的焊接,获得了焊接接头力学性能并分析了接头形成和断裂机制。结果表明,由于搅拌摩擦焊过程中搅拌针的摩擦剪切及对塑化材料的挤压作用,使树脂基体发生塑化并带动碳纤维迁移形成焊接接头,在搅拌头旋转速度950 r/min,焊接速度38 mm/min时,接头拉伸强度可以达到52.43 MPa,接近母材强度的51%,焊接接头的断裂机制主要为基体剪切断裂和纤维-基体界面脱粘。     

Ultrasonic welding of all-polypropylene composites

In this study, the mechanical properties of ultrasonic welded lap joints of all-polypropylene composite (APPC) were investigated and compared to the interlaminar properties of the composite sheet itself. The process control parameter was welding time: welded samples were prepared with an ultrasonic welding machine in the 0.1–1.0 second time range. In most cases, the shear strength of the welded samples exceeded that of the unwelded APPC. Although it was found that during the ultrasonic welding process, the reinforcing tapes partially melted in the welding zone (WZ), the seam remained strong enough because the heat released and the pressure applied during the welding process further improved the consolidation of the APPC layers. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48799.     

Effect of Wood Welding Process on Chemical Constituents of Australian Eucalyptus

Thermochemical changes occurring during wood welding were investigated in Eucalyptus saligna and Eucalyptus pilularis. Unwelded reference wood and material from welded interface were compared via Py-GC/MS, thermogravimetric analyses, X-ray photoelectron spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy to explain differences in mechanical properties of welded wood between species. It appeared that the species originally containing more condensed substructures also provided stronger joints. The condensation index after welding allowed validating that the adhesive properties of lignin are more accessible in such species. The presence of more carbonyl functions, attributed to carbohydrate solicitation during welding process, potentially made lignin less accessible. Changes following welding were evidenced by the contribution of extractive compounds, fatty acid chains, and terpenoids, possibly reacting with hydroxyl groups and leading to adhesive properties by chemical linkage through new covalent bonds formation. Results corroborate the better mechanical properties of E. saligna, providing stronger joints possibly due to more accessible adhesive properties by esterification between lignin and fatty acid.     

Influence of Machine Setting and Wood Parameters on Crack Formation in Scots Pine Joints Produced by Linear Friction Welding

Abstract

Previous investigations on linear welded woods have shown that the connections are not sufficiently resistant to water for use in outdoor conditions. Therefore, they are utilized mainly for non-structural use, with only short time exposure to varying humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood or sapwood on crack formation in the weldline of Scots pine (Pinus sylvestris) were investigated. Axial samples measuring 200 mm × 20 mm × 20 mm from Scots pine were welded, placed vertically in 5-mm-deep tap water and were taken out of the water one at a time after each 10 min of water absorption. Then they were scanned and put back into water until the first crack appeared in the weldline. An X-ray Computer Tomography (CT-) scanner was used to monitor water movement and density change in the weldlines during water absorption–desorption. CT-scanning enabled to detect the cracks as they formed in the weldline and could be used in wood welding studies. Data evaluation showed that all the three studied parameters had significant effects on crack formation and that crack occurrence could be postponed by using heartwood samples with 1.3 MPa welding pressure and 1.5 s welding time.     

排液燃气发生器的设计及参数计算

叙述了爆炸焊接法修复油田井下损伤套管用排液燃气发生器的工作原理,分析了燃气发生器产生的气体对油田井下套管修复时液体流向的作用,并对排液燃气发生器的火药装药量、燃烧室压力、喷嘴尺寸、点火压力、点火药量及壳体强度进行了理论分析和计算。结果表明,利用火药燃烧气体做功所设计的排液燃气发生器可以快速排除套管与焊接加固管之间的井液,可以显著提高爆炸法修复套管的效果。     

Investigations on Mechanical and Metallurgical Properties of Friction Welding of AlB<Subscript>2</Subscript> Reinforced Aluminum Matrix Composites

Friction stir welding (FSW) of AlB₂ reinforced aluminum matrix composites was conducted by varying two process parameters namely rotational speed of the tool and travelling speed. Six welds were made on the metals to determine the optimum level of process parameters for welding aluminum matrix composites. Microstructures evaluation conducted by optical microscopy (OM) and scanning electron microscopy shows the boron particle agglomerations at the interface of joints form larger grain structures in the stir zone (SZ). Mechanical properties were investigated using a tensile strength test and microhardness measurements. The joints made with rotational speed of 1000 rpm and travelling speed of 10 mm/min exhibit the highest strength of 152.7 MPa in the weld zone. The friction coefficient, wear behavior and scratch morphology of the friction stir welded AMCs were studied. The hardness and wear properties improved in the base metal region in comparison to the welded region.     

Joining of wood layers by friction welding

A welding technique has been developed to join wooden work pieces by frictional heat without any wood glue. During the welding process 'melting' of the surfaces, resulting from the influence of pressure and frictional heat, was observed. Solidification and bond formation between the welded pieces happened during cool down of the heat-affected zone. The solidification of the heat-affected zone is explained. Tests were carried out to determine the resistance of the joint as a function of the interfacial temperature and the solidification time. The results show that after 20 s of cooling, the shear strength of the welded bonds amounted to 70% of the ultimate shear strength of the connection after 15 min of solidification. This behaviour allows continuous welding of multilayered wood laminates. Due to the use of natural materials only, the welded products are environmentally compatible. In case of disposal, the welded components can be burned in the same way as natural wood without the evolution of toxic compounds.     

Microstructure and mechanical properties of stainless steel clad plate joints produced by TIG and MAG hybrid welding

Abstract

This paper investigated the microstructure and mechanical properties of Q235/304 stainless steel clad plate welding seam produced by hybrid welding of tungsten inert gas welding (TIG) and metal active gas arc welding (MAG). The results showed that the dual phases containing ferrite and austenite appeared in the stainless steel covering welding (SSCW), while the partial martensite phases appeared in the carbon steel backing welding (CSBW), which is attributed to the dilution behavior of Ni and Cr elements from stainless steel to the Q235 steel results into the movement of the CCT curve to the right side and the decrease of critical martensite formation cooling rate. The CSBW possesses the highest microhardness value in the weld metal due to the existence of the martensite zone. The impact tests were carried out and the results showed that the Charpy absorbed energy of weldments (81?J) is almost equal to that of base clad plate (83?J). The SSCW layer possesses the ductile fracture characteristics accompanying many dimples. However, in the CSBW layer, some cleavage fracture characteristics are presented in the radiation zone while many dimples are located in the fibrous zone, revealing a complex combination of brittle and ductile fracture behavior, which is due to the existence of martensite zone, different stress states and crack propagation velocity.

• Highlights

• Hybrid (TIG, MAG) welding is suitable for welding stainless steel clad plate;

• The martensite formation in CSBW is related to dilution and diffusion of Cr and Ni;

• Partial martensite transformation can strengthen and toughen the welding seam.

     

Total and Soluble Metal Contents in Flux-Cored Arc Welding Fumes

The chemical composition and solubility of metals in welding fumes is thought to be related to the welder health but is not well characterized. We quantified and compared the total (insoluble + soluble) and soluble metal contents in fumes from flux-cored arc welding using non-stainless steel (FCAW/NSS) and stainless steel (FCAW/SS) wire. Welding was performed in an American Welding Society standard fume collection chamber. The total content of 13 analyzed metals was significantly higher in FCAW/NSS fumes than in FCAW/SS fumes (51.6 ± 5.7 vs. 40.2 ± 5.2%, p < 0.001). Soluble metal content was significantly higher in FCAW/SS fumes than in FCAW/NSS fumes (15.5 ± 5.8 vs. 6.49 ± 2.4%, p < 0.001) due to the presence of potassium and sodium. Different proportions of each element were observed between welding types. Iron, magnesium, and aluminum were significantly higher in FCAW/NSS fumes, whereas chromium, nickel, and potassium were more common in FCAW/SS fumes. The metal composition of FCAW fumes was more similar to that of shielded metal arc welding fumes than that of gas metal arc welding fumes. It seems unnecessary to measure soluble iron, nickel, aluminum, and barium to compare with their soluble ACGIH-TLVs at the FCAW welding process. But chromium should be specified in terms of its valance and solubility.     

Wood Welding: Chemical and Physical Changes According to the Welding Time

Wood welding using linear friction is a technique that has been developed in the past five years. The goal of this study was to analyze the microstructure development in the interphase enabling the wood-to-wood adhesion without any adhesive. Chemical and physical analyses have been carried out using infrared thermography, mechanical shear tests, transmitted light microscopy and X-ray densitometry. They have been considered as efficient to qualify the characteristics of the welded joints. The aim of this paper is to present a study using these analysis methods to observe the physical modifications of the wood in the interphase according to the welding time. The welding process of beech wood (Fagus sylvatia) with a welding time between 0 and 11 s could be divided into three different phases. The first phase describes changes in the physical and chemical characteristics of the wood. Densification and anatomical modifications occur in this phase. The second phase represents stabilization of the welded joint. The last phase of the cycle is a conditioning phase. All phases are controlled by the heat spread in the interphase and the time of heat exposure. Various parameters such as welding time, shear strength, temperature and width of the welded joint have been correlated and a hypothesis on the chemical reactions occurring in the interphase has been put forth. This study allowed discovering a window of parameters in which the quality of the welded joint is quite stable. Improving the quality of manufactured welded wood products without adhesive can now be done more easily due to this method.     

玻纤增强热塑性复合材料超声波焊接方法研究

基于对ECR玻纤增强热塑性复合材料的力学和热物理特性以及普通工程塑料超声波焊接理论的研究,借鉴普通工程塑料超声波焊接方法,提出了超声波焊接ECR玻纤增强热塑复合材料制件的新思路;探讨了超声波在ECR玻纤增强热塑性复合材料中的传播及焊接机理。通过调整超声时间、保压时间、焊接压力等工艺参数,使用普通超声波塑料焊机成功焊接了ECR玻纤增强PA66试件。力学性能测试和断口微观组织观测表明,试件焊接区结合良好。     

Development of multiwalled‐carbon‐nanotube‐welded carbon fibers and evaluation of the interfacial strength in epoxy composites

Multiwalled carbon nanotube (MWCNT)‐welded carbon fibers (CFs) were prepared by a three‐step process, which included polyacrylonitrile (PAN) coating, MWCNT absorption, and heat treatment. The structure of these materials was characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy. The MWCNTs were uniformly assembled on the surface of the PAN‐coated CFs and welded by a PAN‐based carbon layer after heat treatment. The contact angle of the MWCNT‐welded CFs in the epoxy resins was 41.70°; this was 22.35% smaller than that of the unsized CFs. The interfacial shear strength (IFSS) of the MWCNT‐welded CF–epoxy composite was 83.15 MPa; this was 28.89% higher than that of the unsized CF–epoxy composite. The increase in the IFSS was attributed to the enhancement of adhesions between the CFs and polymer matrix through the welding of the MWCNTs on the CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45027.     

Analysis on mechanism of explosive spalling resistance of aluminum powder on ladle corundum-based refractory castable

The effect of the particle size (50–325 mesh) and content (0–0.1 wt%) of metallic aluminum powder on the explosive spalling resistance of corundum-based refractory castables were investigated in this study based on air permeability, pore size distribution, heat release, fracture energy and microstructural analyses. The experimental results show that the addition of Al powder significantly improves their explosive spalling resistance. As observed, the explosive spalling resistance of the castables was mainly influenced by the permeability mechanism and the fracture energy. Permeable paths were generated in the microstructure of the sample during the overlapping period between the curing process and the H₂ gas forming one, derived from the Al–H₂O reaction. The highest permeability level was obtained when 0.075 wt % of Al powder with size of 100 mesh was incorporated into the corundum-based refractory castables. At the same time, the fracture energy of the castable samples was increased accordingly.     

L450/316L不锈钢复合钢管对焊缝焊接接头组织性能研究

对壁厚(10+2)mm的L450/316L复合管进行了对焊试验,打底焊及过渡焊采用管内外充氩保护的GTAW焊,填充及盖面焊采用手工电弧焊,并对其焊接接头进行拉伸、刻槽锤断、弯曲、冲击、晶间腐蚀试验评价对焊焊缝的性能,采用光学、扫描电镜(SEM)及能谱分析(EDS)对焊接接头的冲击断口、显微组织及合金元素的进行扩散分析。试验结果表明:接头力学性能良好,耐晶间腐蚀性能较好;焊缝不锈钢层主要有奥氏体、铁素体组成;过渡层组织较细小,可以防止不锈钢层金属中合金元素被扩散层稀释;扩散层组织主要为马氏体、少量的残余奥氏体;合金钢层组织为先共析铁素体、针状铁素体、粒状贝氏体和及少量珠光体。     

Plasma Arc Welding of TiB2–20 vol% TiC

Ceramics consisting of titanium diboride with titanium carbide additions were fusion welded to produce continuous joins. A welding current of 135 A, welding speed of 8 cm/min, and plasma flow rate of 0.75 L/min were combined with a preheat temperature of ~1450°C to fusion weld coupons of TiB₂ containing 20 vol% TiC with a thickness of 4 mm. The resulting fusion zone (FZ) was 3.9 mm deep at the center of the joint and 10.4 mm wide. During cooling of the melt pool, four distinct regions of crystal growth and nucleation were observed due to thermal gradients. Regions at the top and bottom of the FZ exhibited smaller TiB₂ crystals due to higher nucleation rates whereas regions in the middle of the FZ showed higher growth rates, with TiB₂ crystals up to 1.2 mm in length. Thermal gradients also affected cooling of the eutectic phase, causing a cellular structure to appear in the cooled eutectic. Plasma arc welding was a viable method for joining diboride‐based ceramics.     

Laser transmission welding of PMMA to alumina ceramic

In this paper, a method of laser transmission welding on ceramic surface after pulse laser microtexture pretreatment was proposed to address the problem that welding ceramics with high transparency polymers is demanded but difficult to be performed. In this method, the polymer flows into the micro-texture of the blind hole on the surface to form mechanical riveting to enhance the welding strength. The formation characteristics and welding mechanism of PMMA welded joint with micro-texture alumina ceramics were studied experimentally and simulatively. The effects of blind hole microtexture size, continuous laser power and continuous laser scanning rate on solution flow and welding strength were studied. The results showed that the air bubbles formed in the welded seam by entering the micro-texture blind hole and trapped air in the blind hole were the key factors affecting the strength of the joint. A 3D finite element model of the transient temperature field and flow field of polymer during laser welding was established. The simulation results showed that the polymer on the left side of the blind hole melted first when heated and inflowed along the wall due to the effects of self-gravity and buoyancy caused by temperature differences. The gas expanded and extruded upward to the left, forming bubbles in the polymer melt pool and pushing the polymer melt into the blind pore microtexture. Finally, a complete molten pool was formed. The flow of polymer melt, the formation of bubbles and the formation of joint were revealed.     

Influence of Weldling Parameters on Weldline Density and Its Relation to Crack Formation in Welded Scots Pine Joints

Exterior use of welded wood laminates without further treatment is not recommended. Frictional welded joints have poor resistance to moisture variation, especially to drying. Therefore, application of welded woods is limited to interior use without exposure to highly variable air humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood/sapwood on weldline density of Scots pine (Pinus sylvestris) joints were investigated. Interdependence between density and water resistance of weldline (in terms of crack time) was also studied by comparing the results of this investigation with those of the earlier studies. Specimens composed of two wood pieces, each measuring 20 mm × 20 mm × 200 mm, were welded together to form a specimen measuring 40 mm × 20 mm × 200 mm by a vibration movement of one wood surface against another at a frequency of 150 Hz. An X-ray Computerized Tomography scanner was used to measure weldline density. Weldlines of sapwood produced by 1.3 MPa welding pressure and 1.5 s welding time showed the highest density. No correlation between weldline density and crack time was evident.     

Welding of polymer interfaces

Studies of strength development at polymer-polymer interfaces are examined and applications to welding of similar and dissimilar polymers are considered. The fracture properties of the weld, namely, fracture stress, σ, fracture energy, G_Ic, fatigue crack propagation rate da/dN, and microscopic aspects of the deformation process are determined using compact tension, wedge cleavage, and double cantilever beam healing experiments. The mechanical properties are related to the structure of the interface via microscopic deformation mechanisms involving disentanglement and bond rupture. The time dependent structure of the welding interface is determined in terms of the molecular dynamics of the polymer chains, the chemical compatibility, and the fractal nature of diffuse interfaces. Several experimental methods are used to probe the weld structure and compare with theoretical scaling laws, Results are given for symmetric amorphous welds, incompatible and compatible asymmetric amorphous welds, incompatible semicrystalline and polymer-metal welds. The relevance of interface healing studies to thermal, friction, solvent and ultrasonic welds is discussed.