Papers by Keyword: Macrostructure

Abstract: A comparison of middle transverse and longitudinal samples of 6 mm thick FSW AA5083/AA6082 joints is reported in this study. To investigate the differences, the study compares the FSW middle samples, obtained from the two orientations, to the parent materials through metallographic (macro/microstructure) and mechanical (tensile, micro-hardness) tests. The results revealed that the transverse and longitudinal samples had hardness values of 93.90 and 119.27 HV0.2, respectively, whereas the highest tensile strength of the same samples was 130.694 MPa and 127.833 MPa, with strain values of 0.054 and 0.0834, respectively.

Abstract: Efficiency energy is an importance goal in transportation device development. Reducing weight of device is a way to reduce fuel consumption from transportation device, using thin plat in a device or construction could reduce the weight. The originality of this study was Micro Dissimilar Friction Stir Spot welding used to join Cu and Al plate with copper sheet on top the aluminum sheet. Micro welding is a joining thin plat less than 1 mm welded by Friction Stir Spot welding which has been called a Micro Friction Stir Spot welding, using a Pin on the Shoulder. Peak load average, macrostructure and shear strength of a copper and aluminum sheet joint welded by Micro Friction Stir Spot welding were discussed in this study. Copper and Aluminum 0.5 mm could be successfully joined. Shoulder diameter 6 mm effected to the highest peak load, and welding force 50 kgf significantly increased the peak load. Mixing Cu and Al formed in a weld joint. Friction was not complete occurred in shoulder interface and deflection copper sheet formed in around weld nugget because of Pin and Shoulder. A Pin on Shoulder affect to form a joint only around Pin, shear strength could not conclude because the weld joint areas developing tend to an incomplete joining.

Abstract: The paper investigates the technology of production of steel billets continuously cast billets for rolling balls of large diameter. In Kazakhstan, in connection with the development of new copper deposits such as Aktogay and Bozshakol, the need for large diameter steel grinding balls for primary ore processing has increased. The main problem in the operation of large diameter grinding balls is the tendency of the grinding media to break during operation. The authors of the work investigated the process of production of steel billets continuously cast billets with a cross section of 150 × 150 mm for rolling balls of large diameter (d 125 mm) in the PB LLP "KSP Steel", which showed that the breaking of grinding balls is initiated mainly by the presence of internal discontinuities (gas axial looseness) in continuously cast billets. Studies have shown that the technological scheme for the production of grinding balls with a diameter of 125 mm from continuously cast billets with a section of 150 × 150 mm, including steel smelting in an arc furnace with steel finishing on a ladle-furnace unit, deoxidation with aluminum and degassing in a ladle vacuum apparatus, casting steel in a closed jet on a continuous casting and further production of rolled stock on a rough rolling mill ensures the absence of internal discontinuities (gas bubbles, axial looseness) in the workpieces and ensures the production of high quality balls.

Abstract: This work represents the characterization of materials surface before and after laser processing with macrophotography, optical metallography, and scanning electron microscopy before and after thermal exposure. The factors influencing the reliability of the laser-induced code readability have been determined as color and contrast. The range of stability of the code readability under thermal influence on the structural materials under study was determined, which allows improving the reliability of the laser-induced marking codes readability. The research objects in this paper were samples of the following materials: alloys based on copper, aluminum, and iron with laser-induced codes of various types applied on the surface. This work aimed to research the stability of laser-induced codes readability after thermal exposure using macrophotography, optical metallography and scanning electron microscopy on structural materials of various purposes before and after laser processing (when forming a binary matrix code). The research results obtained and presented in this article on the stability of laser-induced codes reading under thermal action on structural materials can be used in different fields of industry, when marking products of heavy, general, medium, and precision engineering, as well as for marking metal products and blank parts. The results of this research are also planned to be used for further analysis of the occurring damage, leading to reading errors due to mechanical and chemical influences. It is planned to evaluate the limit values of the parameters that determine the degree of degradation at which the encoding will be considered to have lost the recognizing ability. Requirements for the quality and permissible code damage will also be developed to ensure their reliable identification.

Abstract: The FSW process has proven to be a promising process for joining steels and improving their characteristics. However, the use of wrongs technological parameters leads to the appearance of defects. In this study, the macro and microstructural characteristics of steel joints and their mechanical properties are analyzed, and the main types of defects of the butt steel joints are presented. The main conclusions of the works studied are summarized and the main development directions for research on the characterization of steel structures joined by the FSW process are identified.

Abstract: In order to prevent distortion caused by heat which affects the material deformation, the properties controlled are required. The properties changes and the placement of the mounting position will effect the weld strength that causes cracks and broken joints, therefore it affects the safety of machine construction. Thus, the objective of this paper is to control the shape of cross member backbone assembly by gas metal arc welding (GMAW). The welding is produced by an automatic robot Yaskawa-MA1440 type. In order to obtain the good quality of the result, the welding shape is controlled by a parameters combination of voltage, current, and speed. Yaskawa-MA1440 type is used as the automatic welding machine. The main material used is cold rolled steel coil sheet MJSC270D-OD with a thickness of 1.2 mm. In addition, to control the welding shape, the specified shape design standard is followed include travel speed, gas flow, welding direction, torch tip distance to the workpiece, torch angle and welding angle. The results of visual and dimensional were also examined in this research. Furthermore, the macrostructure i.e. leg length, fusion penetration, throat thickness have been analyzed and confirmed based on the standards used in the auto body vehicle part company. The appropriate parameters for the finest welding shape are defined at the horizontal position using an electric current of 120 A and the welding voltage of 18 V (± 1 V). Thus, the measurement control of macrostructure is defined as reference parameters for mass production of cross member backbone assembly.

Abstract: The characteristics of the macrostructure of expanded clay concretes are compared using the topological and fractal approaches. The sensitivity of concrete strength to the fractal dimensions of a cement-sand matrix, expanded clay gravel, feldspar grains, large fractions of quartz and pores is verified. The trend of the influence of the expanded clay concrete macrostructure on its strength is determined using the fractal approach. Fractal modeling of the macrostructure of expanded clay concrete made it possible to reduce the forecast error in the indices of their strength by 1.18...2.03 times in comparison with the topological approach.

Abstract: Creating a gradient of properties in a single material is challenging for scientists and engineers. For this purpose, such methods are used as: welding of steels of different chemical compositions, joint rolling of steel sheets, sealing and surfacing of various kinds. All of these methods have a big disadvantage: under load, the material is destroyed in the weakest place - the place where the layers join. In this article, the authors proposed to obtain a gradient of properties in steel castings due to the introduction of dispersed particles of tungsten carbide into the crystallizing melt during centrifugal casting. The particles introduced serve as crystallization centers, accelerate the crystallization process and increase certain types of mechanical properties (hardness, microhardness, tensile strength). In addition, the particles of tungsten carbide have high hardness; therefore, in the structure of the workpieces they serve as reinforcing elements that strengthen the structure. The uneven distribution of particles in the preform being formed is possible for two reasons: tungsten carbide has a density greater than the melt, and besides, centrifugal force acts on them. The article describes the experiment and its results on the production of metal preforms with a gradient of properties. The introduced particles significantly influenced the macro-structure of the prepared castings. The article also presents the results of a study of the effect of particles on the hardness and micro-hardness of the resulting blanks.

Abstract: The friction stir welding of polyamide 66 with a specially modified tool is studied. A variation of the conventional friction stir welding is investigated by incorporating a friction plate for the purpose of heating the polymer in the course of welding process through the tool shoulder. This in turn, improves the efficiency of the weld. The association of the welding process parameters and the weld performance has been investigated by the grey relational analysis with multi response characteristics like weld tensile strength, percent elongation and hardness. Macrostructure of the weld joint cross section has been explored by Stereo microscope. The maximum weld tensile strength of 63 MPa and a Shore hardness of 60 D at the weld nugget are obtained. The hardness profiles of the welded samples have been analyzed in this investigation.

Abstract: The main objective of this study was to carry out more detailed research on the effects of the amount of cement paste on the physical and mechanical properties of porous fine aggregate concrete (PFAC). Fine foamed glass aggregate (prepared of local glass breaks) and crushed expanded polystyrene aggregate (prepared of local packing tare of household equipment), ordinary Portland cement (OPC), plasticizing and air entraining admixtures, as well as pozzolanic additive – metakaolin-based waste (local waste in production process of foamed glass aggregate), were used for the preparation of forming mixtures. Fine aggregates were coated by an extremely thin layer of porous cement paste in the samples with the lowest amount of OPC (70 kg/m³), and the aggregates contact with each other mainly at the points (empty spaces between the aggregates are interconnected between each other). There were no empty spaces between the aggregates observed, and porous cement paste seems to be monolithic in the samples with the highest amount of OPC (370 kg/m³). Increased amount of OPC (from 70 to 370 kg/m³) results in denser structure, increased dry density, compressive strength, thermal conductivity coefficient and decreased water absorption of the samples.