In the present study, wetting behaviors of Sn-9Zn-xAl ternary lead-free solder alloys produced by the addition of Al in various amounts binary Sn-9Zn eutectic lead-free solder alloy (wt%) were investigated. Contact angles of alloys were measured by using of the sessile drop method. Microstructures, inter-metallic phases, and melting temperatures of alloys were characterized by optic microscope and scanning electron microscope and energy dispersive X-ray spectroscopy, X-ray diffraction, and differential scanning calorimeter, and effects of the amount of Al on microstructure were investigated. As a result, the studies show that Al-rich areas were found on microstructure of Sn-9Zn-xAl alloys. The lowest melting temperature for Sn-9Zn-0.5Al and Sn-9Zn-0.7Al alloys was determined as 200.9°C. It was determined that wetting capability of Sn-9Zn-xAl alloys failed because of oxidation.
In this study, microstructure and mechanical properties of modified (Al10Sr) and grain refined (Al5TiB) A356 aluminum alloy were investigated. To determine the effect of modification and grain refining on the microstructure and mechanical properties of A356 alloy, density measurement, optical microscope and scanning electron microscope examinations and tensile tests were performed. As a result of the study, the highest density and the least percentage of porosity were measured for the modified (with Al10Sr) and grain refined (with 1.5% Al5TiB) alloy system. The lowest density values and the highest percentage of porosity were measured for the unmodified and non-grain refined alloy. According to the tensile tests, average ultimate tensile strength and the highest elongation were obtained for the alloy modified with Al10Sr and grain refined with 1.5% Al5TiB alloy. It was determined that average ultimate tensile strength and percentage of elongation increased as the amount of Al5TiB added for grain refinement and modified to A356 alloy increased.
In this paper the influence of alloying elements (Si and Al) on the precipitation process of Mg₂Sn phase in Mg-Sn alloys is presented. X-ray diffraction analysis was used to determine the lattice parameters of α -Mg solid solution, the phases content and size of the Mg₂Sn precipitates. It was found that silicon causes the refinement of the precipitates of Mg₂Sn phase, however it does not result in a significant increase of hardness increment after ageing treatment at 250°C. The addition of aluminum has a positive effect on the hardness of Mg-7Sn-5Si alloy.
Aluminum alloy AA5754 is used for many technical and industrial applications. Twin roll casting is unique among the casting processes in that it is a combined "solidification/deformation" technique. The simultaneous solidification and hot rolling produces characteristic microstructure with a fine cell size and intermetallic particle distribution with some residual structure. In the study, first AA5754 alloy (tread and plain sheet) strips were fabricated by using a twin-roll caster equipped with water-cooled steel-rolls. To reduce the thickness of the strip, cold rolling process was applied until strip thickness got 3 mm. After homogenization step the strips were cut in to smaller specimens and annealed at 260°C, 285°C, 310°C, 340°C, 370°C, 400°C, 430°C, 460°C, 490°C, 520°C for 3 hours to obtain the desired temper conditions. Mechanical properties were investigated after processes. Tensile, hardness and bending tests were applied to monitor the effect of annealing after cold rolling process.
Four different quasi-static flow curve models were investigated to describe flow curves of austenitic (304) and ferritic (430) stainless steel sheets. Uni-axial tensile tests were carried out and material constants of the models were determined by curve fitting technique. Applicability of these models over the uniform plastic deformation region was evaluated according to the value of nonlinear regression parameter R². It was observed, that the predictions made by El-Magd model are in good agreement with the experimental data for both 304 and 430 stainless steel sheets.
Ternary Mg-2Sn-Mn (0.5, 1, 2, and 2.5 wt% Mn) alloys were prepared under vacuum/argon atmosphere controlled furnace to investigate their microstructural and mechanical properties as a potential biodegradable implant material. As-cast alloys were heat treated at 550°C for 24 h and then at 300°C for 16 h. The alloys were characterized as-cast and after the heat treatment by optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness measurement. Mg phase is evident for both as-cast and heat-treated alloys while Mg₂Sn intermetallic phase is detected in all heat treated alloys except Mg-2Sn-0.5Mn. The dendritic microstructure changed to a microstructure with equiaxed grains after the heat treatment. The increase of Mn in ternary Mg-2Sn-Mn alloys resulted in a microstructure composed of smaller grains. Moreover, microhardness of ternary alloys slightly increased with the addition of Mn.
The aim of this study was to fabricate 30 wt.% AlB₂/Al-Cu composites using in-situ casting processes and to investigate the corrosion behavior of the composites and of the matrix material in various media. The electrochemical parameters were obtained from potentiodynamic polarization curves. The composites were prepared by liquid reaction of aluminum matrix with boron oxide at 1400°C. The results show that the corrosion resistance of the composite was higher than that of the matrix in selected corrosion media. The anodic corrosion current density values were decreased by reinforcing AlB₂ particles.
Binary Al-Sn (1, 2, 4, 6, 8 at.% Sn) synthetic alloys were prepared under vacuum-atmosphere controlled furnace. The Al-Sn alloys were coated by plasma electrolytic oxidation technique for 120 min in aqueous electrolyte containing sodium silicate and potassium hydroxide using the same electrical parameters. The microstructure, surface roughness, phase content and chemical composition of the coatings were characterized by scanning electron microscopy, profilometry and X-ray diffractometry. The coating became porous while coating thickness and surface roughness decreased, with increasing amount of Sn content in Al-Sn alloys. The coating was not formed on the Al-Sn alloy with 8 at.% Sn. Plasma electrolytic oxidation coatings were composed of mainly mullite (3Al_2O_3 ·2SiO_2), γ-Al_2O_3 and α-Al_2O_3 up to 4 at.% Sn. The α-Al_2O_3 phase formed as precipitate in the inner region of the coating and its amount decreased with Sn amount in the Al-Sn alloys. The SnO_2 phase was only detected in the coating of Al-6Sn alloy. Scanning electron microscopy - energy dispersive X-ray spectroscopy results showed that the traces of Sn were evident in the oxide coating along with Al, O, Si, Na, and K. The increasing addition of Sn in the alloys resulted in reduction of the overall microhardness of the coating with decreasing manner from dense inner region to the surface of the coatings.
In this study, gas nitriding behavior of 34CrAlNi7-10 steel was investigated. Single stage processes were carried out at 500°C, 520C and 540C for 10, 20, 30 h, respectively. Nitrogen activity on surface was controlled by the nitriding potential K_{N} which is known as thermodynamical control parameter for controlled gas nitriding process. The presence of nitrides formed on surface of test material was determined by X-ray diffraction analysis technique. The morphology of nitrided layer was studied by optical microscope. The microhardness of surface of nitrided sample in HV_1 was observed between 975 and 1132. Choosing the right nitriding potentials for each temperature, which give the same nitrogen concentration and activity on surface by using the Lehrer diagram, showed that all the samples had almost the same surface roughness of R_{a} = 0.28-0.32 μm after gas nitriding cycles. The measurements showed that the white layer thickness varies between 4.38 μm and 28.80 μm and the growth of the layer was strongly affected by process time and temperature. Diffusion depths as Nht (HV) for each experiment were determined and compared.
Binary synthetic aluminum alloys Al-M (M = Mg, Mn, Si) containing 4 at.% alloying elements as substrate materials were prepared under controlled vacuum/argon atmosphere. The substrates were coated by micro arc oxidation (MAO) method for 120 minutes in aqueous alkaline electrolyte using the same electrical parameters. The phase constituents, chemical composition, surface roughness and the microstructure of the coatings were characterized by XRD, profilometry and SEM-EDS. The average coating thicknesses are 127 μm, 91 μm and 78 μm on Al-4Mn, Al-4Mg and Al-4Si alloys, respectively. All MAO coatings were composed of mullite (3Al₂O₃·2SiO₂) and γ-Al₂O₃ phases. In addition to these phases, α-Al₂O₃ phase, in the form of precipitates, was detected in coatings on Al-4Mn and Al-4Mg alloys. The presence of Si, Mn and Mg was detected in the coatings, depending of the chemical content of the substrate alloys.
Thin film brass alloys were galvanostatically electrodeposited from non-cyanide citrate solutions. Aqueous sulphate solutions were used as deposition medium. It was aimed to understand the effect of ultrasonication of the solutions before electrodeposition process. Ultrasonication was not applied during deposition. This method was utilized to change solution characteristics, by applying high energy via cavitation mechanism, which would result in changes in resultant film properties. X-ray diffraction technique was used to investigate phase formation in samples. Moreover X-ray diffractograms were also used to calculate grain size values. Cu and Zn elements were codeposited successfully to form brass alloys. When phase formations in the samples were compared to each other, it was concluded that although there are small differences between X-ray diffractograms of samples, ultrasonic treatment before electrodeposition is not an effective way to alter phase characteristics of CuZn alloy samples, since all samples have shown similar X-ray diffraction graphs. Grain size is found to get smaller with presence of ultrasonication, extending ultrasonication time caused only small random changes in grain size.
Copper zinc alloys were electrodeposited in the form of thin films. Electrodeposition process was carried out in non-cyanide aqueous medium, under constant current. Effect of pre-deposition ultrasonication of solution was investigated. In other words ultrasonic treatment was applied only before the electrodeposition. Solutions were subjected to high-energy ultrasonication for increasing times. Cyclic voltammetry was used to understand changes occurring due to duration of ultrasonication. No ultrasonication was applied during deposition. Atomic composition of resultant films were revealed by MP-AES. It was found that implementation of ultrasonic treatment before electrodeposition affects CV characteristics, when compared to non-ultrasonicated solution. Atomic composition of fabricated samples were found to be close to each other, some of them showing more deviation.
The work presents results of the research on changes in microstructural, and mechanical properties of the structural XAR 400 wear-resistant steel caused by the welding procedure. Metallographic and microhardness studies revealed complex microstructure of the welds that turned out to vary with the distance from the weld axis: predominance of the acicular ferrite (ACF) structures in the weld itself, quasi-polygonal ferrite (QPF) crystals with precipitates of troostite (T) in the heat-affected zone, and the bainitic ferrite (BF) structures in the heat-partially-affected zone.
In this study, oxide coatings were produced on pure zirconium by micro arc oxidation method in the electrolytes containing sodium silicate and different amounts of yttrium acetate tetrahydrate (1-4 g/l) for the same coating duration of 1 h. The surface roughness, microstructure, phase content and chemical composition of the coatings were characterized by using scanning electron microscopy, profilometry and X-Ray diffractometry. It was found that the surfaces of coatings on zirconium consist of monoclinic-ZrO₂, tetragonal-ZrO₂ phases. The coating thickness decreases with addition of yttrium acetate tetrahydrate while it does not change significantly with the increase of its amount. The clustered equiaxed features were formed on the surfaces of the coatings. As the amount of yttrium acetate tetrahydrate in the electrolyte solution increased, the coating/substrate interface smoothened. Two main regions of the coating, the outer dense region (I) and the porous inner region (II), became significant with addition of YAT into the electrolyte.
High-pressure die casting offers reduced costs due to its small tolerances and smooth surface finish. Casting parts produced are consumed by the automotive industry in millions. In this study, the use of computer aided engineering applications on design of high-pressure die-casting was studied. The influence of casting process steps in die design was studied and analyzed. The casting simulation software was used to improve design and solve problems. By using the simulation software in analyses of die design, the final design was reached in a few hours and thus the design process of pre-production was shortened and mold production was carried out with no revision on die material. Radiographic test was applied on the casting parts and the result shows good correlation between simulations of solidification result data. Also the results proved that the application of squeeze pressure in the intensification phase of high-pressure die casting process could be examined in the casting simulation.
Aluminium-boride composites (Al-AlB_2) having two different volume fractions of reinforcing (AlB_2), namely 4.0 and 10.0 per cent have been produced through synthesizing boron by reaction of boron oxide (B_2O_3) with liquid aluminium. Friction and wear characteristic of the composites have been investigated under dry sliding condition and results compared with pure aluminium. The wear rate increases with normal load and sliding speed and is significantly lower with the composites when compared to that of monolithic material. The coefficient of friction increased with increasing volume fraction of AlB_2 reinforcement phase. The wear rate, however, decreased with increasing volume fraction of AlB_2.
Mg-Ca-Gd based alloys are investigated as a potential alloy for degradable biomaterials with some promising results. In this investigation the Mg10CaxGd (x=5, 10, 20) were investigated with synchrotron radiation X-ray diffraction during solidification to follow the phase evolution at two different cooling rates at 5 and 50 K min^{-1}. All three alloys show formation of α -Mg followed by Mg₂Ca phase, while only Mg10Ca20Gd alloy contained Mg₅Gd phase during solidification. During cooling α -Mg was first observed between 628 and 632°C at a cooling rate of 5 K min^{-1} while this decreased to 620-628°C with the increase in cooling rate to 50 K min^{-1}. The change in cooling rate from 5 to 50 K min^{-1} did not change the types of intermetallic phases observed but resulted in suppressing temperatures at which the intermetallic phases were first detected.
In this work the influence of equal-channel angular pressing on strength and fatigue of an aluminum alloy has been studied. Transmission electron microscopy was applied to determine an average grain size, shape, and size of precipitates. The ultimate tensile strength and fatigue endurance limit of ultrafine-grained and coarse-grained samples were evaluated at 20°C and 175°C.
Zirconium (Zr) is a potential implant material due to its excellent biocompatibility and low elastic modulus for biomedical applications. Its poor bioactivity, however, limits its use as biomaterials. In this study, microarc oxidation which is a plasma-electrochemical based process was applied to produce oxide coatings on pure zirconium. The coating processes were conducted in different electrolytes containing sodium silicate and varying amounts of calcium acetate tetrahydrate (CA) for 30 min to investigate the effect of the introduction of CA into the electrolyte solution on the morphology and chemical composition of the fabricated coatings. It was found that the coatings consisted of monoclinic-ZrO₂ and tetragonal-ZrO₂ phases. The amount of the tetragonal-ZrO₂ phase increased with the increasing CA concentration in the electrolyte. The coating thickness and surface roughness showed a tendency to increase with the increasing CA concentration in the electrolyte. It was observed that the vicinity of plasma channels were Zr-rich, while their surroundings were rich in Si and Ca elements. The outer region of the coating was denser compared to inner region consisting of Zr-rich porous structure.
In this study, DP800 (dual phase) steel plates, having 1 mm thickness were joined by copper-based (CuAl8) wire using CMT-brazing (cold metal transfer) technique. Specimens were prepared in joining forms in butt joint configuration. CMT-brazing operations were done under nine different CMT-brazing current intensities of 40, 45, 50, 55, 60, 65, 70, 75 and 80 A. CuAl8 wire, composed largely of copper, was used as the filler metal. Having accomplished the CMT-brazing operations, the tensile properties of joints, and micro- and macro-structures of joints were investigated in order to test the joinability of DP800 steel by CMT-brazing technique.
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