Uğur Gökmen

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.

Mechanical and ballistic properties of powder metal 7039 aluminium alloy joined by friction stir welding

Abstract 7039 Al alloy plates which were used as armor materials were produced by powder metallurgy method. The prepared mixed powders were pressed and plated by extrusion process. These plates, after being subjected to T6 heat treatment, were joined double-sided by friction stir welding method. Microstructure and microhardness of the welded plate were investigated. It was determined that the finest grain structure and the lowest hardness value occurred in the stir zone as 2–6 μm and HV 80.9, respectively. In order to determine the ballistic properties of welded plates, 7.62 mm armor piercing projectiles were shot to the base metal (BM), heat affected zone (HAZ), and thermomechanically affected zone+stir zone (TMAZ+SZ). Ballistic limits ( v 50 ) of these zones were determined. The ballistic limits of the BM, TMAZ+SZ, and HAZ of the plate were approximately 14.7%, 15.3%, and 17.9% lower than that of the standard plate at the same thickness, respectively. It was determined that the armor piercing projectiles created petaling and ductile hole enlargement failure types at the armor plate. Ballistic and mechanical results can be enhanced by hot–cold rolling mills after extrusion and particle reinforcement.

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%.

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.