金属基复合材料连接技术的研究进展

对金属基复合材料的各种连接技术,包括熔融焊接（钨惰性气体焊接、金属情性气体焊接、电子束焊接、激光束焊接、接触电阻焊接、电容放电焊接、等离子体焊接）、固相连接（扩散连接、摩擦连接、磁励电弧对接）、钎焊、胶粘、等离子喷涂连接、快速红外连接等工艺方法进行了系统地分析和总结。简要介绍了各种连接方式的工艺特点和使用范围,重点对等离子体喷涂连接和快速红外连接这两种新型技术的工艺过程进行了较为详细的说明。对各种     

Characteristics of Welding Crack Defects and Failure Mode in Resistance Spot Welding of DP780 Steel

The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three dif-ferent types of welding cracks in welded joints were investigated by optical microscopy,scanning electron microscopy and electron back-scattered diffraction.Finally,the failure mode of the welded joints in shear tensile test was dis-cussed.It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current.The surface crack in welded joint is intergranular fracture,while the inner crack in welded joint is transgranular fracture,and the surface crack on the edge of the electrode imprint can be improved by adding prehea-ting current or tempering current.The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.     

Global and Local Mechanical Properties of Autogenously Laser Welded Ti-6Al-4V

Ti-6Al-4V sheets, 3.2-mm in thickness, were butt welded using a continuous wave 4 kW Nd:YAG laser welding system. The effect of two main process parameters, laser power and welding speed, on the joint integrity was characterized in terms of the joint geometry, defects, microstructure, hardness, and tensile properties. In particular, a digital image correlation technique was used to determine the local tensile properties of the welds. It was determined that a wide range of heat inputs can be used to fully penetrate the Ti-6Al-4V butt joints during laser welding. At high laser power levels, however, significant defects such as underfill and porosity, can occur and cause marked degradation in the joint integrity and performance. At low welding speeds, however, significant porosity occurs due to its growth and the potential collapse of instable keyholes. Intermediate to relatively high levels of heat input allow maximization of the joint integrity and performance by limiting the underfill and porosity defects. In considering the effect of the two main defects on the joint integrity, the underfill defect was found to be more damaging to the mechanical performance of the weldment than the porosity. Specifically, it was determined that the maximum tolerable underfill depth for Ti-6Al-4V is approximately 6 pct of the workpiece thickness, which is slightly stricter than the value of 7 pct specified in AWS D17.1 for fusion welding in aerospace applications. Hence, employing optimized laser process parameters allows the underfill depth to be maintained within the tolerable limit (6 pct), which in turn prevents degradation in both the weld strength and ductility. To this end, the ability to maintain weld ductility in Ti-6Al-4V by means of applying a high energy density laser welding process presents a significant advantage over conventional arc welding for the assembly of aerospace components.     

Effect of welding consumables and processes on dynamic fracture toughness (J 1d) of armour grade Q&T steel joints

Abstract

Austenitic stainless steel (ASS) welding consumables are being used for welding armour grade Q&T steels, as they have higher solubility for hydrogen in the austenitic phase, to avoid hydrogen induced cracking (HIC). Even with austenitic stainless steel consumables under high dilution, the risk of HIC prevailed. In recent years, the developments of low hydrogen ferritic steel (LHF) consumables that contain no hygroscopic compounds are utilised for welding Q&T steels. The use of ASS fillers for welding armour grade Q&T steels creates a duplex microstructure (austenite and δ ferrite) in the welds, which drastically reduces the joint efficiency (ratio of ultimate tensile strength of the joint and the base metal). On the other hand, the weld made using LHF fillers exhibited superior joint efficiency due to the preferential ferrite microstructure in the welds. The use of ASS and LHF consumables for armour grade Q&T steels will lead to formation of distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence on the dynamic fracture toughness of the armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence on the welding consumables and processes on the dynamic fracture toughness properties of armour grade Q&T steel joints. Shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes were used for fabrication of the joints using ASS and LHF welding consumables. The joints fabricated by SMAW process using ASS consumables exhibited superior dynamic fracture toughness values compared to all other joints.     

A study on weldability of zinc-coated steel sheets in lap joint configuration

The weldability of Zn-coated steel sheets 0.7 mm thick was investigated using resistance spot welding process. The effect of welding current, welding time and holding time on weld nugget characteristics, microstructure, and mechanical properties was discussed. Then, the possibility of replacing this welding process with laser beam welding was outlined. In this respect, quality of weld joints as a function of zinc removal by grinding prior to welding was evaluated. It is found that resistance spot welding current and time are the most significant parameters in affecting both expulsion and Zn-induced porosity. Expulsion was avoided and Zn-induced porosity was reduced with the decrease in welding current and/or welding time. Zn-induced porosity was completely eliminated by zinc-removal by grinding prior to welding. The best weld joint concerning nugget characteristics, soundness and tensile shear strength was obtained using welding current of 10 kA, weld cycle of 20, holding cycle of 18. Unlike resistance spot welds, high quality of CO₂ laser welds free from Zn-induced porosity could be made without zinc removal by grinding before welding.     

Evaluation of Microstructure and Mechanical Properties of Laser Beam Welded AISI 409M Grade Ferritic Stainless Steel

 The microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated. Single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3000 mm/min. The joints were subjected to optical microscope, scanning electron fractographe, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into dendritic grains as a result of rapid solidification of laser beam welds. Tensile testing indicates overmatching of the weld metal is relative to the base metal. The joints also exhibited acceptable impact toughness and bend strength properties.     

Joining of thick section steels using hybrid laser welding

Abstract

A recently completed project called Economical and Safe Laser Hybrid Welding of Structural Steel (HYBLAS) has developed the use of hybrid laser welding for thicker section steels up to 690 MPa yield strength. The full project involved several European organisations, was part funded by the European Research Fund for Coal and Steel (ERFCS) and was led by Corus RD&T. This paper presents an outline of those parts of the project which relate to those developments which resulted in being able to laser hybrid weld, in a single pass, up to 25 m plate thickness using 20 kW of laser power at speeds of ～1 m min^-1. Multipass and dual sided welding techniques have also been developed up to 30 mm plate thickness and fillet welds up to 20 mm steel thickness. The project examined the weldability of steels from 180-690 MPa and operational windows for defect free welding were defined. In addition various NDE methods were studied for their efficiency in regard to the defect types which can occur in laser hybrid welds. The fracture and mechanical properties of the joints were shown to be perfectly acceptable for all structural uses and an extensive fatigue testing programme demonstrated that the fatigue behaviour of the welded joints exceeded conventional welding expectations. Finally full scale industrial components were manufactured, inspected and tested to demonstrate that the anticipated fatigue benefits were obtained.     

DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

Properties of Laser Welded SAF 2205 Duplex Stainless Steel Sheet

High rate welding methods for sheet material can offer significant cost reduction for mass production application in comparison with more conventional arc processes. Therefore, in this research, laser welds in SAF 2205 duplex stainless steel (DSS) sheets welded using different welding speeds were investigated. Metallography, texture measurements and mechanical testing were carried out on the weld joints. The corrosion properties were not evaluated. The base material was characterised by a bamboo‐like morphology and a ferrite volume fraction of 53 %. For all welding speeds, the ferrite level in the weld zone was higher than 85 % and the austenite showed an acicular morphology. Whereas in the base material a clear element partitioning existed between ferrite and austenite, no partitioning was observed in the welded zone. This is due to the very high cooling rates, which limit the amount of diffusion that can take place. Electron backscattering diffraction revealed that the texture of the cold rolled material was destroyed by the welding process. While the hardness of the base material was about 265 HV, the maximal hardness in the fusion zone exceeded 310 HV and increased with an increase of the welding speed. Yield and tensile stength were however not dramatically influenced. On the other hand, the formability properties were deteriorated by an increase of the welding speed. This behaviour can also be observed on the fracture surfaces of tensile specimens. The tensile tests on the welded sheet resulted in ductile fracture surfaces, but an easier void formation was observed in the laser welds. However, it has to be pointed out that formability of the laser welded DSS sheets is acceptable when a lower welding speed is used. This is also confirmed by the crack propagation observed during the Erichsen test. Therefore, the laser welding can be used as a joining operation for DSS sheet materials providing the corrosion requirements are fulfilled.     

Ti-6Ta合金等离子焊焊接接头的组织与性能

采用等离子弧焊对3mm及12mm厚Ti-6Ta合金板材进行了焊接实验,通过光学显微镜和腐蚀试验研究了焊接接头的组织形貌和耐腐蚀性能,同时测试了焊接接头的力学性能和弯曲性能。结果表明：采用等离子弧进行焊接的Ti-6Ta合金,其焊接热影响区为粗大的等轴晶粒,焊接熔区晶粒组织则呈粗大的不规则形貌。并且,Ti-6Ta合金等离子焊焊接接头的强度和弯曲性能与母材相当,塑性稍有下降。此外,焊接热应力对接头的强度和弯曲性能影响较小,焊接接头在沸腾硝酸中具有良好的耐腐蚀性能,且焊接接头的耐蚀性对焊接热应力不敏感。     

Mechanical properties of titanium connectors

The tensile mechanical properties of welded titanium joints were studied, and intact titanium was used as controls. Welded joints were fabricated with either a stereographic laser-welding technique or a gas tungsten arc welding technique. The effect of heat treatment following a simulated porcelain application was also investigated. Heat-treated laser welds had significantly lower ultimate tensile strengths. Heat treatment had no effect on the modulus of elasticity or elongation, but generally significantly decreased the yield strength of the titanium specimens. The gas tungsten are welding specimens had significantly higher yield strengths and elastic moduli than the other two groups. The elongation of the control specimens was significantly greater than the elongation of the gas tungsten arc welding specimens, which was in turn significantly higher than that of the laser-welded specimens.     

Characterization Method of Mechanical Properties of Dissimilar Steel Resistance Plug Welding Joints

A novel resistance plug welding process has wide prospects for dissimilar steel. However, until present, there is no effective method to characterize the mechanical properties of resistance plug welding joints. In this paper, the influence factors such as diameter of filler, diameter of surface plastic ring, and diameter of nugget were first used for analysis. Slug ratio and indentation depth (height) ratio were designed to characterize the mechanical properties of the resistance plug welding joints. The results show that smaller the slug ratio, better the mechanical properties of the joint. The tensile shear load of the joint is higher when the indentation depth (height) ratio is 92–102%, and the joint has the best tensile shear load when the indentation depth (height) ratio is 96% or 97% in this study. Slug ratio and indentation depth (height) ratio are suitable for characterizing mechanical properties of dissimilar steel resistance plug welding joints.     

Effect of Welding Parameters on Tensile Properties and Fatigue Behavior of Friction Stir Welded 2014-T6 Aluminum Alloy

The present work describes the effect of welding parameters on the tensile properties and fatigue behaviour of 2014-T6 aluminum alloy joints produced by friction stir welding (FSW). Characterization of the samples has been carried out by means of microstructure, microhardness, tensile properties and fatigue behaviors. The hardness in the softened weld region decreases with decreasing the welding speed. Irrespective of the tool rotation speeds, the best tensile and fatigue properties were obtained in the joints with the welding speed of 80 mm/min. The joint welded with a rotating speed of 1520 rpm at 80 mm/min has given a highest tensile and fatigue properties. The fatigue behaviors of the joints are almost consistent with the tensile properties, especially elongations. Higher ductility in FSW joints made the material less sensitive to fatigue. The location of tensile fractures of the joints is dependent on the welding parameters. On the other hand, the fatigue fracture locations change depending on the welding parameters and stress range. In addition, a considerable correlation could not be established in between heat indexes and mechanical properties of FSW 2014-T6 joints under the investigated welding parameters.     

Comparison of microstructure and properties between joints of FSW and TIG 316L austenitic stainless steel

FSW and TIG were conducted on 316L stainless steel.Variation during microstructure and properties in joints obtained by different welding methods was studied.The results show that the effect of severe mechanical stirring and intense plastic deformation creat a fine recrystallized grain in the welding joint during FSW.As for TIG,the temperature of welding joint exceeds the melting point of welded material itself.The entire welding process belongs to the solidification of a small molten pool;and the microstructure of the joint takes on a typical casting structure.When the welding parameters were selected appropriately,the average ultimate tensile strength of FSW joints can reach 493 MPa,which is 83.6%of base metal;the average elongation is 52.1%of base metal.The average ultimate tensile strength of TIG joints is 475 MPa, which is 80.5%of base metal;the average elongation is 40.8%of base metal.The tensile test of FSW joints is superior to the TIG joints.The microhardness of FSW joint compared to base metal and TIG joint having a significant improvement,which arel95.5 HV,159.7 HV and 160.7 HV,respectively;grain refinement strengthening plays an important role in enhancing the microhardness.The electrochemical corrosion tests show that the joint of FSW 316L austenitic stainless steel has a good corrosion resistance.     

Influence of Filler Wire Diameter on Mechanical and Corrosion Properties of AA5083-H111 Al–Mg Alloy Sheets Welded Using an AC Square Wave GTAW Process

In this work, the influence of filler wire diameter on AA5083-H111 weldments was studied. For that, square butt joints were made using an AC square wave gas tungsten arc welding process with the addition of filler wires of diameter 1.2 and 2.4 mm separately. The experimental results revealed that changing the filler wire diameter influenced the bead geometry and a complete penetration was achieved in both welds. The weldment processed with smaller diameter filler wire consisted of a wider heat affected zone with recrystallized grains and a fusion zone with coarser grain structure, thus reducing the mechanical properties and corrosion resistance. However, the use of larger diameter filler wire assisted in faster torch speed, resulting in lower heat input and thus finer equiaxed grains were produced in fusion zone. Also, finer grains along with the dispersion of finer Al₆(Fe,Mn) particles supported in obtaining the superior tensile and corrosion properties.     

Crystal structure of a murine alpha-class glutathione S-transferase involved in cellular defense against oxidative stress

STATEMENT OF PROBLEM: The electric alloy brazed joints of removable partial denture alloys have failed frequently after routine usage. PURPOSE: A technique providing higher joint strengths was investigated. This investigation compared the tensile strengths of electric-brazed and laser-welded joints for a cobalt-chromium removable partial denture alloy. MATERIAL AND METHODS: Twenty-four cobalt-chromium standard tensile testing rods were prepared and divided into three groups of eight. All specimens in the control group (group 1) were left in the as-cast condition. Groups 2 and 3 were the test specimens, which were sectioned at the center of the rod. Eight specimens were joined by using electric brazing, and the remaining specimens were joined by using laser welding. After joining, each joint was ground to a uniform diameter, then tested to tensile failure on an Instron universal testing machine. Failure loads were recorded and fracture stress calculated. Statistical analysis was applied. RESULTS: The student-Newman-Keuls test showed a highly significant difference between the joint strengths of the as-cast control specimens, the electric-brazed and laser-welded joints. CONCLUSIONS: The tensile strengths of the as-cast joints were higher than those for the laser-welded joints, and both were higher than the electric-brazed joint strengths.     

Crossed-Wire Laser Microwelding of Pt-10 Pct Ir to 316 LVM Stainless Steel: Part II. Effect of Orientation on Joining Mechanism

With the increasing complexity of medical devices and with efforts to reduce manufacturing costs, challenges arise in joining dissimilar materials. In this study, the laser weldability of dissimilar joints between Pt-10 pct Ir and 316 low-carbon vacuum melted (LVM) stainless steel (SS) crossed wires was investigated by characterizing the weld geometry, joint strength, morphology of weld cross sections, and differences in joining behavior, depending on which material is subject to the incident laser beam. With the Pt-Ir alloy on top, a significant amount of porosity was observed on the surface of the welds as well as throughout the weld cross sections. This unique form of porosity is believed to be a result of preferential vaporization of 316 LVM SS alloying elements that become mixed with the molten Pt-10 pct Ir during welding. The joining mechanism documented in micrographs of cross-sectioned welds was found to transition from laser brazing to fusion welding. It is inferred that the orientation of the two dissimilar metals (i.e., which material is subject to the incident laser beam) plays an important role in weld quality of crossed-wire laser welds.     

Metallurgical and Mechanical Characterization of Laser Spot Welded Low Carbon Steel Sheets

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds.     

High cycle fatigue behavior of DP980 steel and DP980 steel laser welded joints

For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks.