Browsing by Author "Yagci, T"

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    Effect of the substrate surface and coating powder hardness on the formation of a cold sprayed composite layer
    Kahraman, AD; Kahraman, F; Culha, O; Yagci, T
    In this study, the powder hardness and substrate surface hardness on the coating formation in the cold spray process was investigated. The AA6082 aluminum alloy hardened by the shot-peening process was used as the base material. Two different metallic powders and a ceramic particle powder were used as powder materials with different hardness. Thus, the powder particles from different materials were sprayed onto the surface under the same spraying process conditions. In order to obtain a workpiece surface with different hardness values, shot-peening treatment was applied to the substrate material at different treatment times. According to the microstructural examination, the harder metallic coating powder has accumulated more and the lower hardness metallic coating powder has accumulated less when the substrate material hardness increases. Al2O3 particles in the layer formed were distributed close to homogeneous. Furthermore, the size of Al2O3 particles near the contact surface has become much finer especially in the long-term shot peened samples due to their higher hardness. From the indentation experiments, the elastic behavior and recovery amount of the composite coating layer increased due to the increase of the substrate surface hardness, and the stress distributions were performed less after the load was removed.
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    Aluminum Alloy Development for Wheel Production by Low Pressure Die Casting with New Generation Computational Materials Engineering Approaches
    Yagci, T; Cöcen, Ü; Çulha, O
    Computational Materials Engineering (CME) is a high technological approach used to design and develop new materials including the physical, thermal and mechanical properties by combining materials models at multiple techniques. With the recent advances in technology, the importance of microstructural design in CME environments and the contribution that such an approach can make in the estimation of material properties in simulations are frequently discussed in scientific, academic, and industrial platforms. Determination of the raw material characteristics that can be modeled in a virtual environment at an atomic scale by means of simulation programs plays a big role in combining experimental and virtual worlds and creating digital twins of the production chain and the products. In this study, a new generation, alternative and effective approach that could be used to the development of Al-Si based wheel casting alloys is proposed. This approach is based on the procedure of optimizing the physical and thermodynamic alloy properties developed in a computer environment with the CME technique before the casting phase. This article demonstrates the applicability of this approach in alloy development studies to produce Al-Si alloy wheels using the low pressure die casting (LPDC) method. With this study, an alternative and economical way is presented to the alloy development studies by trial and error in the aluminum casting industry. In other respects, since the study is directly related to the automotive industry, the reduction in fuel consumption in vehicles is an expected effect, as the new alloy aims to reduce the weight of the wheels. In addition to conserving energy, reducing carbon emissions also highlights the environmental aspects of this study.
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    Investigation of metallurgical properties of Al-Si-Mg casting alloys with integrated computational materials engineering for wheel production
    Yagci, T; Cöcen, Ü; Çulha, O; Armakan, E
    In this study, integrated computational materials engineering, which is one of the new generation approaches in materials science, was used in the production of aluminum alloy wheels by low pressure die casting method. In casting alloys, the efficiency of grain refinement provided by master alloys added to the melt decreases with increasing silicon content of the alloy. In this context, as-cast properties of silicon reduced (Si: 5.0 wt.%) alloys with different Mg ratios (Mg: 3.0, 5.0, 7.0 wt.%) are discussed using integrated computational materials engineering approaches. It has been evaluated whether the examined alloys can be an alternative to the AlSi7Mg0.3 alloy, which is currently used traditionally in the production of aluminum-based wheels, with their microstructural and mechanical properties. The study consists of three stages which are computer-aided production, pilot production, testing and characterization studies. In computer-aided production, original sub-eutectic compositions were determined in types and amounts of alloying elements, alloy designs were realized and a database was created with a computational materials engineering software. Then, low pressure die casting analysis were performed in a virtual environment by transferring these data directly to the casting simulation software. Thus, the microstructural and mechanical properties of the wheel were obtained computationally on the basis of the varying alloy composition. In the second stage, the virtually designed alloy compositions were prepared and sample wheels were manufactured by the low pressure die casting method on an industrial scale. In the testing and characterization phase, spectral analyses, macro and microstructural examinations, hardness measurements and tensile tests were carried out. As a result of this study, it was determined that the studied alloys could be used in the production of wheels by the low pressure die casting method considering the metallurgical properties expected from the wheel. In addition, it is thought that the mathematical design of the material with integrated computational materials engineering approaches before casting simulations will play an active role in the competitiveness and sustainability of the aluminum industry in technological conditions.
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    EFFECTS OF AIR-COOLING-HOLE GEOMETRIES ON A LOW-PRESSURE DIE-CASTING PROCESS
    Pehlivanoglu, U; Yagci, T; Culha, O
    A significant precondition for the production of high-quality castings is keeping an optimum temperature of the respective parts of the die cavity surface. This temperature depends on the temperature of the material, the quantity of metal, the method of cooling the casting die, the thermal conductivity of the die material, and the time during which the casting remains in the die. In addition, the cooling characteristics of alloy steel dies, used in the production of aluminum- alloy wheels with the low pressure die casting (LPDC) method, have critical effects on the mechanical and metallurgical properties of the product. Ducted air coolers are widely used for the cooling of these alloy steel dies. However, the geometrical designs of the air-cooling holes are limited. In this study, we define the effects of the geometry of the cooling holes on the cooling power of the die, the efficiency of the air consumption with the Full Factorial Experimental Design method and to determine the optimum values for LPDC. Pilot production has been carried out on an industrial scale to verify the data obtained by experimental design. The experimental and real data were compared based on the values of the yield strength and the secondary dendrite arm spacing in the microstructure.
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    Comparative study on the thermal and tribological properties of PA12 and PA11 for coating applications
    Basaran, S; Türkmen, I; Yagci, T; Kanbur, K; Bastürk, SB
    In this study, the performance and potential applicability of polyamide-12 (PA12) as an alternative to polyamide-11 (PA11), which is currently used in the coating processes of sliding tools present in cardan shafts, was investigated. The advantages of PA12 powder instead of PA11 in cardan shafts' coating include ease of supply and cost-effectiveness, while still achieving similar performance. Therefore, PA12 is a more economical choice for coating applications. The PA11 and PA12 neat polymers were characterized via differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Based on the analyses, PA12 demonstrated substantial advantages over PA11. It showed a 16 degrees C improvement in decomposition temperature and a 50% increase in crystallinity, enhancing stability under operational conditions, whereas PA11 exhibited approximately 6-7% higher values in crystallization and melting temperatures. The wettability behavior of the steel substrates coated with those polyamides was measured via contact angle analysis. Wear properties and morphologies of coatings were examined using a ball-on disc test and scanning electron microscopy, respectively and comparatively. Furthermore, PA12 typically displays 30% lower wear rates and similar deformation patterns in tests, thereby presenting itself as a cost-effective and widely accessible option for coating applications in comparison to PA11.
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    Optimization of T6 Heat Treatments for AlSi5Mgx Alloys via Computational Materials Engineering and Experimental Validation for Automotive Applications
    Korkmaz, A; Yagci, T; Culha, O
    In this study, T6 heat treatments were applied to AlSi5Mgx (x: 0.3, 0.5, 0.7 wt.%) alloys, fabricated through the low pressure die casting technique. Optimization of these treatments was conducted utilizing computational materials engineering (CME) methodologies, simulation techniques, and design of experiment studies. The objective is to position the investigated alloys as potential substitutes for the heat-treated AlSi7Mg0.3 alloy commonly employed within the automotive sector, with a focus on enhancing microstructural and mechanical characteristics. A comparative analysis was conducted between virtual and empirical data through laboratory-scale experimental investigations. Utilizing the Taguchi experimental design methodology, heat treatments were administered to the spoke region of the wheels, employing three distinct parameters: solution treatment, aging temperature, and time. The analysis outcomes underwent assessment employing the Taguchi method, analysis of variance, and regression analyses, facilitating an exploration into the effects of heat treatment conditions on the physical and mechanical attributes of the alloys. The AlSi5Mg0.5 alloy exhibited optimal mechanical properties when subjected to a solution treatment temperature of 550 degrees C, an aging temperature of 180 degrees C, and an aging time of 4 h. Furthermore, a notable similarity was observed between the analysis outcomes derived from CME methodologies and experimental studies. This concurrence lends credence to the accuracy and reliability of the employed software.
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    Effect of Chip Amount on Microstructural and Mechanical Properties of A356 Aluminum Casting Alloy
    Kaya, AY; Ozaydin, Ö; Yagci, T; Korkmaz, A; Armakan, E; Çulha, O
    Aluminum casting alloys are widely used in especially automotive, aerospace, and other industrial applications due to providing desired mechanical characteristics and their high specific strength properties. Along with the increase of application areas, the importance of recycling in aluminum alloys is also increasing. The amount of energy required for producing primary ingots is about ten times the amount of energy required for the production of recycled ingots. The large energy savings achieved by using the recycled ingots results in a significant reduction in the amount of greenhouse gas released to nature compared to primary ingot production. Production can be made by adding a certain amount of recycled ingot to the primary ingot so that the desired mechanical properties remain within the boundary conditions. In this study, by using the A356 alloy and chips with five different quantities (100% primary ingots, 30% recycled ingots + 70% primary ingots, 50% recycled ingots + 50% primary ingots, 70% recycled ingots + 30% primary ingots, 100% recycled ingots), the effect on mechanical properties has been examined and the maximum amount of chips that can be used in production has been determined. T6 heat treatment was applied to the samples obtained by the gravity casting method and the mechanical properties were compared depending on the amount of chips. Besides, microstructural examinations were carried out with optical microscopy techniques. As a result, it has been observed that while producing from primary ingots, adding 30% recycled ingot to the alloy composition improves the mechanical properties of the alloy such as yield strength and tensile strength to a certain extent. However, generally a downward pattern was observed with increasing recycled ingot amount.
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    Investigation of microstructural and mechanical properties of hot forged 31Mn4 dual phase steel with computer-aided simulations
    Kilerci, I; Çulha, O; Yagci, T
    In this study, it is aimed to realise the hot forging process design and prototype production of the steel yielding support connection clamp, the critical safety element of underground mining ground support systems, by using 31Mn4 dual phase steel. In this context, at the end of the forging and deburring processes, air cooling was designed, simulated and cooling rates were obtained. The cooling curve was integrated into the continuous cooling transformation diagram and phase formation was predicted. The distribution of pearlitic, ferritic, bainitic structures and formation rates, hardness distributions, strength data were also obtained. The hardness and tensile strength calculations, microstructural examinations and SEM analysis were carried out for validation. It has been determined that pearlitic-ferritic microstructures are formed in regions where the cooling rate is slow. In thinner sections where the cooling rate is around 1.2 degrees C/sec, ferritic structures become smaller and bainite phase was observed. As a result, the average tensile strength in 1st and 2nd regions were recorded as 684.5, 690 MPa in simulation, while these values were recorded as 688.45 and 694.15 MPa in tensile tests. It has been determined that this result corresponds to the 99.4% accuracy rate of the prototype obtained by simulation-supported and real productions.