Arif Uzun

The effect of production parameters on the foaming behavior of spherical-shaped aluminum foam

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 investigation of mechanical properties of B4C-reinforced AlSi7 foams

Abstract 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 B 4 C Reinforced/Unreinforced Foamable Aluminium Composites

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.

Investigation of mechanical properties of tubular aluminum foams

Abstract 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%.

Friction stir welding of foamable AlSi7 reinforced by B4C

Abstract Friction stir welding was successfully performed on B4C-reinforced 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.

ALSİ7 KÖPÜKLERİN GÖZENEK MORFOLOJİSİ ÜZERİNE B4C İLAVESİNİN ETKİSİ

Bu calismada toz metalurjisi yontemi ile uretilmis AlSi7 kopuklerin gozenek morfolojisi uzerine B 4 C ilavesinin etkisi incelenmistir. Bu amacla Al icerisinde % 1 TiH 2 , % 7 Si ve degisik oranlarda (% 2, 4 ve 6) B 4 C tozlari ilave edilerek karistirilmistir. Daha sonra karisim tozlar 400 MPa altinda sikistirilmistir. Elde edilen blok numuneler ekstruzyon ve haddeleme islemlerinden gecirilerek kopurebilir malzemeler uretilmistir. Uretilen numuneler farkli sicakliklarda (690, 710, 730 ve 750 °C ) serbest halde kopurtme islemine tabi tutulmustur. Deneysel sonuclara gore; dusuk kopurtme sicakliklarinda B 4 C takviyeli numuneler, parcacik icermeyen numunelere oranla daha dusuk hacimsel genlesme sergilemistir. Genlesme degerleri kopurtme sicakligindaki artisa bagli olarak artmistir. Numunelerin tamamina yakininda 750 °C kopurtme sicakliginda maksimum oranda hacimsel genlesme degerleri (% 350 - % 400) elde edilmistir. B 4 C miktari ve kopurme sicakliktaki artis ile birlikte numunelerde kuresellik faktoru ve gozenek boyutlarinin arttigi, gozenek sayisinin ise azaldigi tespit edilmistir.

TOZ METALURJİSİ YÖNTEMİYLE ÜRETİLEN AlSi7 KÖPÜKLERİN DÜŞÜK HIZLI DARBE ENERJİLERİ ALTINDA PENETRASYON DAVRANIŞININ İNCELENMESİ

Bu calismada AlSi7 kopuklerin dusuk hizli darbe enerjileri altindaki penetrasyon davranislari incelenmistir. Bu amacla toz metalurjisi yontemi ile uretilen 55x55x20 mm boyutlarinda Al kopuklere agirlik dusurme test cihazi kullanarak farkli hizlarda (1,2 - 3 ms -1 ) darbeler uygulanmistir. Bir numune uzerinde delinme meydana gelene kadar yapilan darbe testleri ile saplanma ve delinme darbe davranislari incelenmistir. Darbe sonrasi numunelerin icyapilarinda meydana gelen degisiklikler makro boyutta incelenmistir.

Investigation of Modal Properties of AlSi7 Foam Produced by Powder Metallurgy Technique

Abstract The modal properties of aluminum-based (AlSi7) metallic foam, produced by powder metallurgy technique, as a function of foam density (and thus pore size and amount of porosity) were investigated. In the experimental studies, 1 wt.-% TiH2 and 7 wt.-% Si powders were added to aluminum powder and they were mixed in a three dimensional turbola mixer for 30 minutes. Mixed powders were compacted, extruded and rolled to produce the precursor samples. AlSi7 foam samples with the dimensions of 18.7 cm × 2.6 cm × 1.6 cm were produced after foaming at 690 °C. After all, the natural frequencies and the modal loss factors of a few foam samples with different pore distributions and/or densities were determined using the frequency response functions measured on the test samples. The results show that the densities of the foam samples decrease with increasing pore size and amount of porosity, and the modal loss factors of foam samples increase as foam density decreases.

Effect of Foaming Agent on the Structure and Morphology of Al and Alumix 231 Foams Produced by Powder Metallurgy

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.