Browsing by Author "Uzun A."

Now showing 1 - 20 of 20

Compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams
(2017-09-26) Uzun A.
This paper describes the compressive crush behaviour of spheres of closed-cell aluminium foams with different diameters (6, 8 and 10 mm) and square tubes filled with these spheres. The spheres of closed-cell aluminium foams are net spherical shape fabricated via powder metallurgy methods by heating foamable precursor materials in a mould. The square tubes were filled by pouring the spheres of closed-cell aluminium foams freely (without any bonding). The compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams were compared to that of the empty tubes. The results show a significant influence of the spheres of closed-cell aluminium foam on the average crushing load of the square tubes. The energy absorption in the square tube filled with spheres of closed-cell aluminium foam with diameters of 10 mm is higher than in the other square tubes. The spheres of closed-cell aluminium foams led to improvement of the energy absorption capacity of empty tubes.
Compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams
(2017-09-26) Uzun A.; Uzun, A
This paper describes the compressive crush behaviour of spheres of closed-cell aluminium foams with different diameters (6, 8 and 10 mm) and square tubes filled with these spheres. The spheres of closed-cell aluminium foams are net spherical shape fabricated via powder metallurgy methods by heating foamable precursor materials in a mould. The square tubes were filled by pouring the spheres of closed-cell aluminium foams freely (without any bonding). The compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams were compared to that of the empty tubes. The results show a significant influence of the spheres of closed-cell aluminium foam on the average crushing load of the square tubes. The energy absorption in the square tube filled with spheres of closed-cell aluminium foam with diameters of 10 mm is higher than in the other square tubes. The spheres of closed-cell aluminium foams led to improvement of the energy absorption capacity of empty tubes.
Effect of foaming agent on the structure and morphology of Al and Alumix 231 foams produced by powder metallurgy
(2011-01-01) Turker M.; Ozcatalbas Y.; Cinici H.; Gokmen U.; Uzun A.
In this study various amounts of foaming agent (TiH2 % 0,5-1-1,5-2 ) were added to Al and Alumix 231 powders (Al-Cu %2,5-Mg %0,5-Si %14) and mixed for 30 minutes in a three dimensional turbula. Mixed powders were compacted and then foamed freely at 690°C. Effect of foaming agent on the structure, shape and distribution of pores together with linear expansion, density of the foam and wall thickness of the cell of both materials were investigated. In all conditions foam produced from Alumix 231 powders had more homogenous distribution of the pore compare to the sample produced from pure Al powders. © (2011) Trans Tech Publications.
Electrochemical, mechanical, and antibacterial properties of the AZ91 Mg alloy by hybrid and layered hydroxyapatite and tantalum oxide sol-gel coating
(2023-11-01) Albayrak S.; Gül C.; Emin N.; Gökmen U.; Karakoç H.; Uzun A.; Çinici H.
Friction stir welding of foamable AlSi7 reinforced by B4C
(2016-06-01) Uzun A.; Turker M.
Friction stir welding was successfully performed on B4Creinforced foamable AlSi7 materials produced via a powder metallurgy route. Starting materials of 1 wt.% TiH2, 7 wt.% Si and 6 wt.% B4C were mixed with aluminum matrix powder. Mixed powders were then pressed, extruded and rolled for the production of foamable materials. Microstructural and macrostructural examination along with microhardness and tensile tests were performed to evaluate the weld zone characteristics of foamable materials welded by friction stir welding. Tunnels or needle-shaped gaps were observed in the macrostructures of the weld zones of samples joined at 1 250 rpm and 2 000 rpm rotational speeds. Moreover, the rough surface in the welding zone of materials decreased with increasing rotational speed. Defect-free joints were observed for samples at 1 600 rpm rotational and 40 mm min-1 traverse speeds. There was no significant difference between the microstructures of the weld zone and the base material in terms of particle size and distribution. It was observed that the B4C particles in the nugget zone were partly directed or clustered as a result of the physical mixing. Ultimate tensile strength values of B4C-reinforced foamable AlSi7 materials joined by friction stir welding were found to be lower compared to the base material. The maximum ultimate tensile strength of 135 MPa was obtained at a 1 600 rpm rotational speed and 40 mm min-1 traverse speed. The minimum tensile strength in the samples of 95 MPa was obtained at a 1 250 rpm rotational speed and 80 mm min-1 traverse speed. In all welding conditions, the hardness in the nugget zone increased compared to the base material.
Investigation of mechanical properties of SiC-reinforced seamless aluminium pipes fabricated using powder metallurgy followed by hot extrusion
(2022-10-01) Yurt O.E.; Uzun A.
In this study, SiC (0, 5, 10, 15, 20 wt.%) reinforced seamless aluminium pipes were fabricated using powder metallurgy followed by hot extrusion. The microstructural (optical microscopy, scanning electron microscopy) and mechanical (tensile and crush behaviour) properties of silicon carbide reinforced seamless aluminium pipes were studied. Experimental results showed that the SiC particles form some clusters in the Al matrix and were oriented in the direction of extrusion. Tensile tests indicated that the addition of SiC particles to pure Al matrix resulted in a significant increase in tensile properties of the SiC-reinforced seamless aluminium pipes. Compared to pure Al pipe, 20 % SiC reinforced aluminium pipe exhibited higher yield strength (127 vs. 83 MPa, increased by ∼53 %) and ultimate tensile strength (150 vs. 129 MPa, increased by ∼16 %). Two types of deformation mode (symmetrical ring and asymmetric diamond) were observed in the samples with L/D:1 and L/D:2 ratios under crushing load. Maximum initial collapse force (6.7 kN) was obtained in 10 % SiC reinforced aluminium pipe with L/D:1 ratio.
Investigation of mechanical properties of tubular aluminum foams
(2016-11-01) Uzun A.; Karakoc H.; Gokmen U.; Cinici H.; Turker M.
This manuscript focuses on the mechanical behavior under compressive and bending loadings of tubular aluminum foams. The tubular structures were manufactured using the powder metallurgy technique. Tubular aluminum foams were fabricated by heating foamable precursor materials above their melting temperature in a mould. The influence of important parameters such as wall thickness and density of foam on the mechanical properties was investigated. It was found that the 6 mm thick specimen showed a lower collapse strength than the thicker 9 mm specimen. Despite the decrease in densities of the samples, the collapse strength increased with the increase in wall thickness. The reduction of approximately 33 % in wall thickness (from t = 9 mm to 6 mm) decreased the bending performance of the tubular aluminum foams by approximately 50 %.
Landscape Ecological Evaluation of Cultural Patterns for the Istanbul Urban Landscape
(2022-12-01) Aksu G.A.; Tağıl Ş.; Musaoğlu N.; Canatanoğlu E.S.; Uzun A.
With the widespread population growth in cities, anthropogenic influences inevitably lead to natural disturbances. The metropolitan area of Istanbul, with its rapid urbanization rate, has faced intense pressure regarding the sustainability of urban habitats. In this context, landscapes comprising patches affected by various disturbances and undergoing temporal changes must be analyzed, in order to assess city-related disturbances. In this study, the main objective was to understand how urbanization changed the function of the spatial distribution of the urban mosaic and, more specifically, its relationship with the size, shape, and connection among land-use classes. For this purpose, we took Besiktas, a district of Istanbul, as the study area. We evaluated the landscape pattern of the urban environment in two stages. First, we used medium-resolution satellite imagery to reveal the general interactions in the urbanization process. Landscape- and class-level landscape metrics were selected to quantify the landscape connectivity, and the distances between classes (green areas and artificial surfaces), patterns, and processes, using five satellite images representing a time span of 51 years (1963, 1984, 1997, 2005, and 2014). The general landscape structure was examined by looking at the temporal–spatial processes of artificial surface and green areas obtained from these medium-resolution satellite images. The trends in selected landscape-level metrics were specified and discussed through the use of a moving window analysis. We then used Pleiades high-resolution satellite imagery (2015) to analyze the landscape structure in more detail. This high-resolution base image allows us to recognize the possibility of classifying basic cultural landscape classes. The findings regarding the spatial arrangement of each class in the areas allocated to 14 cultural landscape classes were interpreted by associating them with the landscape functions. Finally, particulate matter (PM10) concentration data were collected and evaluated as an ecological indicator, in order to reveal the relationships between landscape structure and landscape function. In short, we first evaluated the whole landscape structure using medium-resolution data, followed by the classification of cultural landscapes using high-resolution satellite imagery, providing a time-effective—and, therefore, essential—auxiliary method for landscape evaluation. This two-stage evaluation method enables inferences to be made that can shed light on the landscape functions in an urban environment based on the landscape structure.
Production of aluminium foams reinforced with silicon carbide and carbon nanotubes prepared by powder metallurgy method
(2019-09-01) Uzun A.; Uzun, A
In this study, aluminium foams reinforced with silicon carbide and carbon nanotubes were produced by powder metallurgy method. The master alloy aluminium powder (AlSi12)was used as the matrix material, titanium hydride (TiH2)powder was used as a foaming agent and silicon carbide (SiC)particles and carbon nanotubes (CNTs)were used as reinforcing elements. Therefore, 1% of TiH2 by weight and different proportions of SiCx/CNTy (x: 0%, 2%, 4%, 6%, y: 0%, 0.2%, 0.5%, 0.8%, 1%)were added into the master alloy AlSi12 powder and mixed. The mixed powders were further pressed at a pressing pressure of 600 MPa and a temperature of 430 °C. The pressed samples were subjected to the extrusion process at 430 °C, and samples having diameters of 11.76 mm were produced. The foamable precursor materials that were obtained in this manner were subjected to the foaming process at a temperature of 750 °C. The experimental results exhibited that the relative density values of more than 94% were obtained from the foamable precursor materials. It was determined that the CNT and SiC particles significantly affected the elastic–plastic deformation behaviour of the precursor materials. Further, increasing tendencies have been observed in the case of Young's modulus and averege stress in composite foams depending on an increase in the number of CNT and SiC particle.
Production of aluminium foams reinforced with silicon carbide and carbon nanotubes prepared by powder metallurgy method
(2019-09-01) Uzun A.
In this study, aluminium foams reinforced with silicon carbide and carbon nanotubes were produced by powder metallurgy method. The master alloy aluminium powder (AlSi12)was used as the matrix material, titanium hydride (TiH2)powder was used as a foaming agent and silicon carbide (SiC)particles and carbon nanotubes (CNTs)were used as reinforcing elements. Therefore, 1% of TiH2 by weight and different proportions of SiCx/CNTy (x: 0%, 2%, 4%, 6%, y: 0%, 0.2%, 0.5%, 0.8%, 1%)were added into the master alloy AlSi12 powder and mixed. The mixed powders were further pressed at a pressing pressure of 600 MPa and a temperature of 430 °C. The pressed samples were subjected to the extrusion process at 430 °C, and samples having diameters of 11.76 mm were produced. The foamable precursor materials that were obtained in this manner were subjected to the foaming process at a temperature of 750 °C. The experimental results exhibited that the relative density values of more than 94% were obtained from the foamable precursor materials. It was determined that the CNT and SiC particles significantly affected the elastic–plastic deformation behaviour of the precursor materials. Further, increasing tendencies have been observed in the case of Young's modulus and averege stress in composite foams depending on an increase in the number of CNT and SiC particle.
Production of aluminum foam sandwich with various geometric shapes and investigation of their compressive properties
(2013-01-01) Uzun A.
In this study, various sandwich foam structures manufactured from Al/Si7 foams, by using powder metallurgy route, have been investigated. For production of Al foam, 1%wt foaming agent (TiH2) and 7%wt Si powders were added to Al powders and mixed. Mixed powders were compacted, sintered, extruded and rolled to produce foamable precursor samples. Then these samples were applied to the foaming process to produce spherical, cylindrical and rectangular samples. Sandwich structures were produced by placing of foamable precursors in between the Al sheets and then compression test was performed. The results obtained indicate that, dimensional limitation can be overcome by using PM route. However, compressive properties and energy absorption of spherical and cylindrical layered sandwich structures were found to be lower compared to traditional sandwich foam structure.
Production of melt-spun al-20si-5fe alloy and boron carbide (B4C) Composite material
(2018-01-01) Fatih Kilicaslan M.; Uzun A.; Karakose E.
In this study, metal matrix composite materials containing melt-spun Al-20Si-5Fe alloys and boron carbide was produced by high energy ball milling and then hot pressing at 200 MPa pressure and 450°C. Mechanical and microstructural characterizations were performed by using an optical microscopy, X-Ray diffractometer, and dynamic microhardness tester. It was observed that boron carbide particles were homogenously distributed in the microstructure and values of microhardness and elastic modules were averagely 830 MPa and 42 GPa, respectively.
Production of MWCNT-Reinforced Aluminum Foams Via Powder Space-Holder Technique and Investigation of their Mechanical Properties
(2022-09-01) Abo sbia A.E.S.; Uzun A.
In this study, aluminum foams reinforced with multi-walled carbon nanotubes (0%, 0.5%, 1%, and 2% by weight) were produced by powder metallurgy method using different proportions of spherical urea (15%, 30%, and 50% by weight) as space holder. It analyzes the pore morphology and pore distribution of the produced composite foams and examines their mechanical properties under qua-static compressive loading. The results show that the effect of multi-walled carbon nanotubes existing in the cell wall on pore morphology and pore distribution was insignificant. The highest hardness value (65 HV) was determined in the foam samples containing 2% multi-walled carbon nanotube produced with 15% urea. Composite aluminum foam samples with 30–69% porosity and 0.84–1.90 g cm−3 density were successfully produced. The compression properties of the samples decreased with the decrease in the relative densities.
The effect of B4C addition on pore morphology of the ALSI7 foams
(2015-01-01) Uzun A.; Türker M.
In this study, the effect of B4C addition on pore morphology of the AlSi7 foams produced via powder metallurgy method was examined. For this, 7 % Si, 1 % TiH2 (foaming agent) and B4C powders at various rates (2, 4 and 6 %) were added to the Al powders and then mixed properly. Mixed powders were compacted at 400 MPa and extruded and rolled to produce precursor material. Then produced samples were freely foamed at temperatures between 690 °C and 750 °C in order to produce closed cell metallic foams. As a result of experimental studies, the volumetric expansion rate of B4C reinforced preform materials has been found to be lower than AlSi7 foams. Expansion values was found to be increase with increasing the foaming temperature. The maximum volumetric expansion values (350 % - 400 %) in nearly all samples was obtained at 750 °C foaming temperature. Pore size and sphericity factor were increased with foaming temperature and the amount of B4C in the samples but they reduced the number of pores.
The effect of production parameters on the foaming behavior of spherical-shaped aluminum foam
(2014-01-01) Uzun A.; Turker M.
The effect of production parameters on the foaming behavior of spherical-shaped aluminum foam was studied. Elemental powders of Alumix 231 and 1% TiH2 were mixed, compacted at 600 MPa pressure by using a uniaxial action press to produce blanks with 50×30×10 mm in dimensions. These blanks were pre-heated at 550 °C in a furnace for 180 min and then deformed by 10, 30, 50 and 70% by using an eccentric press. They were cut into square shape and foamed at temperatures between 650 °C and 710 °C. It was experimentally found that, the volume expansion rate of foam increases but the maximum foaming duration decreases with increasing the deformation rate and foaming temperature. In these studies 70% deformation and 3.5 minutes foaming duration were found to be the best for the production of spherical foams. This was determined by obtaining the maximum expansion, lower density and homogeneously distributed pores with spherical foams. It was also found that 10% deformation rate was not enough for foaming.
The effect of welding speed on the weld seam profile in MAG and TIG/MAG hybrid arc welding
(2017-04-01) Uzun A.; Uzun, A
The effect of welding speed on the weld seam profile in MAG and TIG/MAG hybrid arc welding was investigated in a low carbon steel. AISI 1020 steel materials having 5 mm thickness were used in the experiments. A fixed MAG and TIG welding currents (90 A and 100 A, respectively) and three different welding speeds (0.14, 0.21 and 0.30 m/min) were selected for welding process for a 100 mm long weld. The welded specimens were cut into several cross-sections; then metallographic tests were performed. The effect of TIG/MAG hybrid arc welding process was compared with the conventional MAG welding. The study showed that welding speed and the selected method have influence on the penetration and that the ratio of penetration depth / weld seam width is increased with increasing welding speed. This increase is more pronounced in TIG/ MAG hybrid arc welding compared to conventional MAG welding. The microstructure of the weld metal was also changed relatively by variation of welding speed. With all welding parameters, the weld metal hardness is higher than hardness of the HAZ and the base metal.
The effect of welding speed on the weld seam profile in MAG and TIG/MAG hybrid arc welding
(2017-04-01) Uzun A.
The effect of welding speed on the weld seam profile in MAG and TIG/MAG hybrid arc welding was investigated in a low carbon steel. AISI 1020 steel materials having 5 mm thickness were used in the experiments. A fixed MAG and TIG welding currents (90 A and 100 A, respectively) and three different welding speeds (0.14, 0.21 and 0.30 m/min) were selected for welding process for a 100 mm long weld. The welded specimens were cut into several cross-sections; then metallographic tests were performed. The effect of TIG/MAG hybrid arc welding process was compared with the conventional MAG welding. The study showed that welding speed and the selected method have influence on the penetration and that the ratio of penetration depth / weld seam width is increased with increasing welding speed. This increase is more pronounced in TIG/ MAG hybrid arc welding compared to conventional MAG welding. The microstructure of the weld metal was also changed relatively by variation of welding speed. With all welding parameters, the weld metal hardness is higher than hardness of the HAZ and the base metal.
The investigation of mechanical properties of B4C-reinforced AlSi7 foams
(2015-09-01) Uzun A.; Turker M.
In this study, the mechanical properties of B4C-reinforced AlSi7 foams produced by using a powder metallurgy method were investigated. For this purpose, Al foams containing B4C at various ratios (0, 2, 4 and 6 %) were prepared with dimensions of 30 × 30 × 14 mm and 110 × 15 × 14 mm for compression and bending tests. Both tests were performed at a 1 mm min-1 strain rate. According to the experimental results, the compressive stress of B4C-reinforced/unreinforced AlSi7 foams, whose relative densities were close to each other, for 10 % strain increased about 15% with the addition of B4C. Although energy absorption values of B4C-reinforced/unreinforced AlSi7 foams were in a complex correlation for 60 % strain, the amount of absorption energy increased with the increase in relative density and the amount of B4C. Bending strength increased due to strain hardening that occurs with the addition of B4C to AlSi7 foams. While maximum bending strength was 0.9 kN in unreinforced materials, it was ∼1.15 kN in 6 % B4C-reinforced AlSi7 foams. Thus, the bending strength of B4C-reinforced materials is higher by ∼ 28 %.
The investigation of mechanical properties of B4C-reinforced AlSi7 foams
(2015-08-01) Uzun A.; Turker M.
In this study, the mechanical properties of B4C-reinforced AlSi7 foams produced by using a powder metallurgy method were investigated. For this purpose, Al foams containing B4C at various ratios (0, 2, 4 and 6 %) were prepared with dimensions of 30 × 30 × 14 mm and 110 × 15 × 14 mm for compression and bending tests. Both tests were performed at a 1 mm min-1 strain rate. According to the experimental results, the compressive stress of B4C-reinforced/unreinforced AlSi7 foams, whose relative densities were close to each other, for 10 % strain increased about 15% with the addition of B4C. Although energy absorption values of B4C-reinforced/unreinforced AlSi7 foams were in a complex correlation for 60 % strain, the amount of absorption energy increased with the increase in relative density and the amount of B4C. Bending strength increased due to strain hardening that occurs with the addition of B4C to AlSi7 foams. While maximum bending strength was 0.9 kN in unreinforced materials, it was ∼1.15 kN in 6 % B4C-reinforced AlSi7 foams. Thus, the bending strength of B4C-reinforced materials is higher by ∼ 28 %.
Vickers Microhardness Studies on B4C Reinforced/Unreinforced Foamable Aluminium Composites
(2018-02-01) Uzun A.; Asikuzun E.; Gokmen U.; Cinici H.
In this work we have investigated the effects of production processes on the structural and mechanical properties of B4C reinforced/unreinforced foamable aluminium composite materials. All samples were produced with the powder metallurgy method. The production method included compression, extrusion and rolling processes. The Vickers microhardness test was applied to determine the mechanical properties of the samples. Vickers microhardness, elastic modulus and yield strength values of the samples were separately calculated and compared with each other. The experimental microhardness results were analysed using Meyer’s law, the proportional sample resistance model, the elastic–plastic deformation model and the Hays Kendall (HK) approach. The results determined that the HK approach was the most suitable model among the other applied microhardness models.