مکانیزم نفوذ فلاکس در جوشکاری تیگ برای آلیاژ آلومینیوم

Study of mechanism of activating flux increasing

weld penetration of AC A-TIG welding for aluminum alloy

مطالعه مکانیزم افزایش مکانیزم نفوذ فلاکس فعال ساز جوشکاری AC  A-TIG

برای آلیاژ آلومینیوم

ABSTRACT

When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld penetration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc constriction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased.

  

اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

Studies on the Effect of Mechanical Vibration on 

the Microstructure of the Weld Metal

تحقیقات در مورد اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

ABSTRACT

The solidification process in the weld metal produces solidification structure. The solidification process depends on the thermal gradient, solidification speed and the alloy content. These structures can be planar, cellular, columnar dendritic and equiaxed dendritic. The solidification process may change from planar to cellular, columnar dendritic and equiaxed dendritic across the weld metal zone as shown in fig.1. Three grains are shown to grow epitaxially from the fusion line. A short distance away from the fusion line, solidification changes to the cellular mode. Further away from the fusion line, the solidification changes to columnar dendritic mode. Near the weld centre line equiaxed dendrites nucleate and grow, blocking off the columnar dendrites. Each one of these structures would affect the hot cracking susceptibility in greater or smaller extent.

تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

Effect of the welding heat input on residual stresses in butt-welds of dissimilar pipe joints

اثر ورودی حرارت جوشکاری بر تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

ABSTRACT

This study used finite element techniques to analyse the thermo-mechanical behaviour and residual stresses in dissimilar butt-welded pipes. The residual stresses at the surface of some weld specimens were measured experimentally by using the hole-drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a modelling procedure with reasonable accuracy was developed. The developed finite element modelling was used to study the effects of welding heat input on magnitude and distribution of welding residual stresses in butt-welded pipes made of ferritic and austenitic steels. The hoop and axial residual stresses in dissimilar pipe joints of 8 mm thick for V-groove shape were studied. It is shown that the welding heat input has a significant effect on magnitude and distribution of residual stresses in the stainless steel side of the studied joints.

  

اتصال با استفاده از تغییرشکل پلاستیک

Joining by plastic deformation

اتصال با استفاده از تغییرشکل پلاستیک

ABSTRACT

Vehicles such as aircraft and cars comprise a large number of mechanical parts produced by a variety of manufacturing processes. Cars generally consist of 10,000–30,000 parts, and the number of parts in aircraft is counted in millions. A trend in manufacturing such products is that both the number of parts and their complexity are increasing, including new combinations of dissimilar materials. Welding, adhesive bonding and mechanical fastening are typically used to join components during product assembly. In fusion welding, workpieces are joined by the application of an external heat source which melts material around the interface. Although the use of welding is widespread, the high temperatures required may reduce the quality, accuracy and reliability of joined parts. The strength of adhesively bonded and mechanically fastened joints is almost always lower than that achieved by welding. Commercial requirements for higher performance, higher productivity and lower cost in joining operations are becoming more demanding. In addition, strong joining of dissimilar materials is increasingly required. For example, high strength steel and aluminium sheets must be joined in some current car models, to allow weight reduction. There is therefore a need to identify new joining methods for new applications and materials.

 

سیلان مواد در طول جوشکاری اصطکاکی اغتشاشی Ti-6Al-V

Material Flow During Friction Stir Welding of Ti-6Al-4V

سیلان مواد در طول جوشکاری اصطکاکی اغتشاشی Ti-6Al-V

ABSTRACT

6 mm thick Ti-6Al-4V butt joints were produced with a tracer material embedded in the joint under a variety of process conditions, namely rotational speed and traversing speed, in an attempt to relate the welding process parameters to the material flow behavior via post weld radiographic and metallographic evaluations. It was found that by embedding refractory alloy powder into the joint line, welding through it, and subsequently x-raying the joint, the material flow patterns could be examined. The tracer material was distributed over a wider area in the weld zone relative to its starting position, implying a fair amount of mixing occurred even though little vertical movement of the tracer material was observed. There was minimal effect of material flow patterns as a function of welding parameters observed using the tracer material and radiographic examination, but defect formation in the root, where there was no tracer material, examined by cross sectional metallographic evaluations were found to be dependent on the rotational speed and traversing speed conditions. Lack of penetration defects were generally associated with relatively “cold” welding conditions (low rotational speed/high traversing speeds) and voids with “hot” conditions (high rotational speed/low traversing speeds).

 

اثر عملیات حرارتی در جوشکاری انفجاری فولاد زنگ نزن/مس

Effect of heat treatment on bonding interface in explosive welded
copper/stainless steel

اثر عملیات حرارتی روی فصل مشترک اتصال در جوشکاری انفجاری فولاد زنگ نزن/مس

ABSTRACT

In this investigation, explosive welding and heat treatment processes provided an effective method for manufacturing high-strength and high-ductility copper/ austenitic stainless steel couple. In order to improve diffusion in the interface of copper/stainless steel, first the tensile samples were provided from the welded part, then they were subjected to annealing at 300 C (below recrystallization temperature) for 8–32 h with 8 h intervals and then samples were cooled in the furnace. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilized to evaluate the possibility of diffusion in the joints. Moreover, in order to measure the hardness of the samples, microhardness test was performed. Microstructural evaluations showed that the stainless steel 304L had a wavy interface. Furthermore, the post heat treatment process resulted in great enhancement of diffusion. Microhardness measurements showed that the hardness of the sample near to the interface is greatly higher than other parts; this is due to plastic deformation and work hardening of copper and stainless steel 304L in these regions. The interface of samples with and without the post heat treatment was exhibited ductile and brittle fracture, respectively.

 

ارزیابی ساختار در اتصال نفوذی آلیاژ تیتانیوم/فولاد زنگ نزن

THE EVOLUTION CHARACTERISTICS AND NUMERICAL
ANALYSIS OF DIFFUSION BONDING INTERFACE
STRUCTURE OF TITANIUM ALLOY/Cu/STAINLESS STEEL

ارزیابی خصوصیات و آنالیز عددی ساختار در فصل مشترک اتصال نفوذی آلیاژ تیتانیوم/فولاد زنگ نزن

ABSTRACT

Carries on the investigation to the titanium alloy/Cu/stainless steel intermetallic compound of bonding interface in the meantime, to make a thermodynamic model of the interface element diffusion to have a numerical simulation of the diffusion distance and diffusion temperature, time. Using analysis methods of stretching test, microhardness test, SEM and EDS, to investigate and research the mechanical properties, the interface structure characteristic, the principal element atomic diffusion mechanism of joints thermal simulation and the vacuum diffusion bonding of Ti-6Al-4V/Cu/304, the reacting phases are produced and the distribution range . The results show that when bonding prssere is 5.0 MPa ، the joints tensile strength first increase and then decreases, with bonding temperature and time rising, When bonding temperature is 1223K, bonding time is 3.6 ks, there is a maximum tensile strength that is 162.73 MPa. However, it will is disadvantageous to performance of the joints, when bonding temperature and time extended overly. It formed multi-phase transition organizations by solid solution, intermetallic compounds in the bonding interface, such as Ti2Cu, TixCuy , Ti2Fe, TiFe2 and TiFe. Effect of TixFey on strength of the joints is slightly inferior the TixCuy compound. The fracture is mainly by the titanium alloy side region III for the source dehiscence, developing in the weak diffusion layer.

 

اتصال نفوذی آلیاژ مس به فولاد زنگ نزن تحت فشار ناگهانی

Impulse pressuring diffusion bonding of a copper alloy to a stainless

steel with/without a pure nickel interlayer

اتصال نفوذی آلیاژ مس به فولاد زنگ نزن تحت فشار ناگهانی همراه با یک لایه ی نیکل خالص بین آن ها و یا بدون آن

ABSTRACT

Impulse pressuring diffusion bonding of a copper alloy to a stainless steel was performed in vacuum. Using Ni interlayer of 12.5 lm, the joint produced at 825 C under 5–20 MPa for 20 min exhibited lower strength, which could result from the insufficient thermal excitation and plastic deformation. At 850 C under 5–20 MPa for 5–20 min, the strength of the joint improved with time. An optimized joint strength reached up to 217.2 MPa. Fracture occurred along the Cu–Ni reaction layer and the Ni layer and almost plastic fracture was confirmed by extensive dimples on the fracture surface. Using the interlayer of 50 lm, the fracture surface was similar. Without Ni assistance, under the same bonding condition, the joint strength was about 174.2 MPa. The lowered strength might be attributed to the appearance of some unbonded zones in the joint. Lots of brittle fracture areas appeared on the fracture surface.

  

ساختار اتصالات جوشکاری شده فولادهای هاردوکس

Structure and hardness changes in welded joints of Hardox steels

ساختار و تغییرات سختی در اتصالات جوشکاری شده فولادهای هاردوکس (Hardox)

ABSTRACT

In the article, the structure and change in hardness of the welded Hardox 400 and Hardox 500 steels have been presented. It has been shown that structures of lower wear resistance are being created as a result of welding those materials in the “as delivered” state (i.e. with the tempered martensite structure) within the heat-affected zones. They are as much as up to 90 mm wide, and that causes their non-uniform and fast wear in the anticipated applications. Based on microscopic tests and hardness measurements a method of thermal joints treatment has been proposed, consisting in their hardening and low-temperature tempering (self-tempering) at the heat-affected zones. It leads to reproduction of that area structure, similar to the native material structure. In the laboratory conditions, a heat treatment differing from the usual practice (stress-relief annealing or normalizing) has not led to welding incompatibilities (cracks).

 

مقایسه جوشکاری EBW و اتصال خود فشاری حرارتی برای آلیاژ Ti6Al4V

A comparative study on electron beam welding and

rigid restraint thermal self-compressing bonding for Ti6Al4V alloy

بررسی مقایسه ای جوشکاری پرتوی الکترونی

و اتصال خود فشاری حرارتی سخت مقیدشده برای آلیاژ Ti6Al4V

ABSTRACT

This study focuses on the influence of joining method difference on the joint microstructure and properties. Unlike vacuum electron beam welding (EBW) utilizing electron beam as fusion heat source, rigid restraint thermal self-compressing bonding (TSCB), a new solid-state bonding method proposed by authors, employs vacuum electron beam as the non-melt heat source to bond materials in this work. Meanwhile, a comparative study on the microstructure and mechanical properties of EBWjoint and rigid restraint TSCB joint was conducted to investigate the effect of this difference on joint microstructure and properties. Results show that compared with EBW joints, the rigid restraint TSCB joints as solid-state joints are homogeneous in terms of microstructure and microhardness profile. Strength of both joints are comparable with that of base metal, but the elongation of the rigid restraint TSCB joint is more close to that of base metal. Rigid restraint TSCB joint has better combination of strength and ductility.