اتصال آلیاژهای آلومینیوم 5083 و 6061 به روش جوشکاری اصطکاکی تلاطمی

Joining of 5083 and 6061 aluminum alloys by friction stir welding

اتصال آلیاژهای آلومینیوم 5083 و 6061 به روش جوشکاری اصطکاکی تلاطمی

ABSTRACT

Friction stir welding (FSW) has emerged as a new solid state joining technique [1], especially for aluminum alloys [2–6]. In this process, a rotating tool travels down the length of contacting metal plates, and produces a highly plastically deformed zone through the associated stirring action. The localized heating zone is produced by friction between the tool shoulder and the plate top surface, as well as plastic deformation of the material in contact with the tool [1].

At the present time, FSW is used mainly for joining similar materials. For dissimilar welding, there have been few systematic studies aimed at clarifying the effect of material combination and welding conditions on weld properties [7, 8].

 

بافت‌های مقاوم در برابر شکست پلی پروپیلن تقویت‌شده با الیاف بلند

An integral design and manufacturing concept for crash resistant

textile and long-fibre reinforced polypropylene structural components

یک طراحی انتگرالی و ایده‌ی تولید برای بافت‌های مقاوم در برابر شکست

و ترکیبات ساختاری پلی پروپیلن تقویت‌شده با الیاف بلند

ABSTRACT

For the design of crash resistant structures for automotive applications, mainly metallic materials are currently considered. However, the advanced specific energy absorption capacity and a high lightweight potential qualifies fiber and textile reinforced thermoplastic composites for such components. With a load adapted material design as well as an efficient manufacturing concept these properties can be exploited to a full extend. A seat pan is chosen as an exemplary structure to illustrate the four main aspects of the investigations: evaluation of glass fiber polypropylene composite configurations; development of a manufacturing and process chain; crash and impact experiments on structural level and numerical modelling strategy. Hybrid yarn based textiles, such as a commercially available 2/2-twill fabric and novel multi-layered flat bed weft-knitted fabrics have been considered to be combined with a long-fibre reinforced thermoplastic material (LFT, cutting length of 25 mm) for complexly loaded sections like ribbings. A special emphasis is set on a similar to mass-production manufacturing process. A fully automated integral hot pressing process has been developed, where an automated handling system places the conglomerate of extruded LFT-material and preheated hybrid yarn textile in a fast-stroke press, achieving process cycles of 45 s. Finally, the structural evaluation under crash loading conditions is compared against numerical results

 

تئوری جدید تأثیر مدیوم بر شبیه سازی انتقال حرارت مواد متخلخل

A novel effective medium theory for modelling

the thermal conductivity of porous materials

تئوری جدید تأثیر متوسط بر شبیه سازی انتقال حرارت مواد متخلخل

ABSTRACT

A novel effective medium theory was proposed to model the thermal conductivity of porous materials. In this theory, phases (or components) are treated as small spheres dispersing into an assumed uniform medium with the thermal conductivity km. A simple algebraic expression for the thermal conductivity based on this theory was derived, in which each has a distinct physical basis. The expression can unify five basic structural models (Series, Parallel, two forms of Maxwell–Eucken, effective medium theory) through variations of km. Furthermore, the feasibility of the model was evaluated using the experimental data from previous literatures and those calculated by this model.

 

اثر فشار اکسیژن بر خواص فیلم های ZnO دوپ شده با Nb

Influence of oxygen pressure on the structural, electrical and optical

properties of Nb-doped ZnO thin films prepared

by pulsed laser deposition

اثر فشار اکسیژن بر خواص ساختاری، الکتریکی و نوری فیلم های ZnO

دوپ شده با Nb آماده شده توسط لایه نشانی لیزری پالسی

ABSTRACT

Nb-doped zinc oxide (NZO) transparent conductive thin films with highly (0 0 2)-preferred orientation were deposited on glass substrates by pulsed laser deposition method in oxygen ambience under different oxygen pressures. The as-deposited films were characterized by X-ray diffraction (XRD), Field emission-scanning electron microscopy (FE-SEM), electrical and optical characterization techniques. It was found that a desirable amount of oxygen can reduce the related defect scattering and enhance the carrier mobility. The resistivity and average optical transmittance of the NZO thin films are of 10−4 Ω cm and over 88%, respectively. The lowest electrical resistivity of the film is found to be about 4.37 × 10−4 Ω cm. In addition, the influence of oxygen pressure on optical properties in NZO thin films was systematically studied as well.

 

ممانعت از خوردگی مس توسط ترکیب bipyrazole در 3% NaCl

Inhibition of copper corrosion by bipyrazole compound

in aerated 3% NaCl

ممانعت از خوردگی مس توسط ترکیب bipyrazole در 3% NaCl هوادهی شده

ABSTRACT

The corrosion behaviour of copper in aerated 3% NaCl solution was investigated by rotating electrode at various rates. The reduction of O2 obeys the Levich equation. The inhibition of the copper corrosion in aerated 3% NaCl solution was studied by using potentiodynamic polarisation and linear polarisation resistance (LRP) in the presence of different concentrations of a bipyrazolic compound named N,N-bis (3-carbomethoxy-5-methylpyrazol-1-ylmethyl) cyclohexylamine (BiPyA). The presence of this compound in the solution decreases the corrosion current density and increases the linear resistance polarisation. The inhibition efficiencies obtained from cathodic Tafel plots and LRP methods are in good agreement. BiPyA compound presents an efficient inhibitor of copper corrosion, acts as a mixed-type inhibitor and adsorbs on the copper surface according to the Langmuir isotherm model.

 

خواص مکانیکی و ساختاری آلیاژ استحکام بالای AISI 4340

Mechanical properties and microstructural features of AISI 4340

high-strength alloy steel under quenched and tempered conditions

خواص مکانیکی و ویژگی‎های ریزساختاری آلیاژ استحکام بالای AISI 4340

تحت شرایط کوئنچ و بازپخت 

ABSTRACT

In this work, the mechanical properties and microstructures of AISI 4340 high strength alloy steel under different tempering conditions are investigated. The specimens are quenched and tempered to a martensite structure and loaded to fracture at a constant strain-rate of 3.3×10−4 s−1 by means of a dynamic material testing machine (MTS 810). The mechanical properties and strain-hardening exponent are considered as function of the tempering conditions. The morphological features of the as-quenched martensite and their evolution during tempering are described. Fractographs of the specimens are also made in order to analyse their fracture and embrittlement mechanisms. The results indicate that the mechanical properties and microstructural features are affected significantly by tempering temperature and holding time. The strength and hardness of tempered martensite drop as the tempering temperature and holding time are increased. However, the ductility increases with increasing tempering temperature and holding time, except when tempered martensite embrittlement occurs. Microstructural observations reveal that the carbide precipitates have a plate-like structure at low temperatures, but are spheroid-like at high temperatures. Under the tested conditions, the fracture appearances show that the material failed in a ductile manner except for the case of tempering at 300°C, where tempering martensite embrittlement occurs due to the existence of retained interlath austenite..

 

مقدمه ای بر دایکست با فشار بالا و عیوب رایج در دایکست

Introduction Of High Pressure Die-Casting

And Common Defects In Die-Casting

مقدمه ای بر دایکست با فشار بالا و عیوب رایج در دایکست 

ABSTRACT

Die casting is a manufacturing process that can produce geometrically complex metal parts through the use of reusable molds, called dies. The die casting process involves the use of a furnace, metal, die casting machine, and die. The metal, typically a non-ferrous alloy such as aluminum or zinc, is melted in the furnace and then injected into the dies in the die casting machine. There are two main types of die casting machines - hot chamber machines (used for alloys with low melting temperatures, such as zinc) and cold chamber machines (used for alloys with high melting temperatures, such as aluminum). The differences between these machines will be detailed in the sections on equipment and tooling. However, in both machines, after the molten metal is injected into the dies, it rapidly cools and solidifies into the final part, called the casting. 

 

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.

 

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

Effect of sample size on intermetallic Al2Cu microstructure and

orientation evolution during directional solidification

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

و روند جهت گیری آن در حین انجماد جهت دار

ABSTRACT

Al-40% Cu hypereutectic alloy samples were successfully directionally solidified at a growth rate of 10 μm/s in different sizes (4 mm, 1.8 mm, and 0.45 mm thickness in transverse section). Using the serial sectioning technique, the three-dimensional (3D) microstructures of the primary intermetallic Al2Cu phase of the alloy can be observed with various growth patterns, L-shape, E-shape, and regular rectangular shape with respect to growth orientations of the (110) and (310) plane. The L-shape and regular rectangular shape of Al2Cu phase are bounded by {110} facets. When the sample size was reduced from 4 mm to 0.45 mm, the solidified microstructures changed from multi-layer dendrites to single-layer dendrite along the growth direction, and then the orientation texture was at the plane (310). The growth mechanism for the regular faceted intermetallic Al2Cu at different sample sizes was interpreted by the oriented attachment mechanism (OA). The experimental results showed that the directionally solidified Al-40% Cu alloy sample in a much smaller size can achieve a well-aligned morphology with a specific growth texture.

 

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

Investigation of carbon nanotube reinforced

aluminum matrix composite materials

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

ABSTRACT

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.