Microstructural evolution during friction stir welding of AlSi1MgMn alloy

This paper provides the research of the infl uence of geometric and kinematic parameters on the microstructure and mechanical properties of welded joint of aluminum alloy AlSi1MgMn (6082-T6) obtained through the Friction Stir Welding (FSW) process. The experiment parameters were welding speed, rotation speed, angle of pin slope, pin diameter and shoulder diameter. On the obtained welded workpieces the dynamic testing on the impact toughness, and determination of microstructural zones were carried out

Mikrostrukturni razvitak AlSi1MgMn slitine tijekom zavarivanja trenjem

This paper provides the research of the influence of geometric and kinematic parameters on the microstructure and mechanical properties of welded joint of aluminum alloy AlSi1MgMn (6082-T6) obtained through the Friction Stir Welding (FSW) process. The experiment parameters were welding speed, rotation speed, angle of pin slope, pin diameter and shoulder diameter. On the obtained welded workpieces the dynamic testing on the impact toughness, and determination of microstructural zones were carried out.U radu se istražuje uticaj geometrijskih i kinematskih parametara na mikrostrukturu i mehanička svojstva zavarenog spoja od aluminijske slitine AlSi-1MgMn (6082-T6) dobivene postupkom zavarivanja trenjem (ZT). Parametri provedenih pokusa su brzina zavarivanja, kutna brzina okretanja alata, kut nagiba trna, promjer trna i promjer čela alata. Kod dobivenih zavarenih uzoraka izvedena su dinamička ispitivanja na udarnu žilavosti i određene su mikrostrukturne zone

Influece of the austempering temperature on the tensile strength of the austempered ductile iron (ADI) samples

Austempered Ductile Iron (ADI) is a class of ductile iron subjected to a two-step heat treatment process – austenitization and austempering. The heat treatment gives to ADI a high value of tensile strength and an especially good strength-to-weight ratio. However, designers in most cases are unfamiliar with this material that can compete favorably with steel and aluminum castings, weldments and forgings. The high tensile strength of ADI is the result of its unique ausferrite microstructure. In this paper, an investigation of the influence of the austempering temperature on the tensile strength of the ADI samples is presented

Liver cystic echinococcosis in humans — a study of 30 cases

The aim of this study is to demonstrate the clinical manifestations and diagnostic approach to liver hydatid disease and suggest its treatment. The prospective study was carried out on 30 patients with liver hydatidosis. Hepatologic examinations were based on: medical history, physical examination, biochemical and serological tests, ultrasonography and computed tomography scanning. Twenty-five (83.3 %) patients underwent radical cyst resection, while in 5 (16.7 %) cases liver resection with left lobectomy was also performed. Hydatid cyst was histopathologically verified in all the patients. Our results showed that the patients with multiple cysts had impaired functional liver tests significantly more often than patients with unilocular cyst. In addition, ultrasonography and computed tomography scans are the valid imaging procedures in diagnosis. Radical, surgical resection of hepatic hydatid cysts is the goal of treatment

Geographical and biological analysis of the water quality of Bovan Lake, Serbia

In this work we performed a complex geographical analysis of the Bovan Lake basin, Serbia, as well as an analysis of the physical, chemical and biological parameters of water reservoir during a one-year period. The basic sanitary characteristics and physical, chemical and biological parameters, necessary for understanding locality conditions, were studied, and the saprobity index, class of quality, index O/H, degree of saprobity, degree of trophicity and category based on the phosphatase activity index (PAI), were determined. Our results classify the ecosystem as polytrophic. The degree of saprobity is oligosaprobic - beta mesosaprobic, with a catarobic degree in winter, classifying the water as III - IV class of quality. Due to the presence of organic residues, a domination of heterotrophic bacteria in comparison to oligotrophic bacteria is evident. The ability of autopurification is weak. The results indicate the need for continual monitoring of the water quality and environmental protection of Bovan Lake

Characterization of red mud/metakaolin-based geopolymers as modified by Ca(OH)2

Geopolymers are an emerging class of materials that offer an alternative to the Portland cement as the binder of structural concrete. One of the advantages is that the primary source of their production is waste alumosilicate materials from different industries. One of the key issues in geopolymer synthesis is the low level of mechanical properties due to porosity as well as the high activity of conductivity carriers. It can often lead to limited application possibilities, so the objective is to obtain an enhanced strength as well as decreased cracking tendency through microstructure modification. The introduction of Ca(OH)2, under certain pH conditions could lead to the filling-the-pores process and improving the mechanical properties. The aim was to understand the role that calcium plays in the geopolymer synthesis, and to define which reaction prevails under the synthesis conditions: formation of geopolymer gel or calcium silicate hydrate that contains aluminum substitution (CASH). The synthesis was performed with different raw materials (with or without red mud) and different alkalinity conditions. Ca(OH)2 was the obligatory supplement to both of the mixtures. Different techniques were performed for the testing of reaction products, as well as to define the microstructural changes as the generator of improved mechanical properties and changed electrical conductivity. The characteristics of the geopolymer's macrostructure were defined by means of an SEM analysis. Compressive strength and electrical conductivity are among the investigated product's properties. X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR) were used for the identification of various crystalline phases and an amorphous phase

Geographical and biological analysis of the water quality of Moravica spring in the Sokobanjska Moravica drainage basin, Serbia

In this work we performed a geographical analysis of the Moravica spring locality in the Sokobanjska Moravica drainage basin in Serbia, as well as an analysis of the physical, chemical, and biological parameters of the water during a one-year period. The basic sanitary characteristics and physical, chemical, and biological parameters, necessary for understanding locality conditions, were studied, and the saprobity index, class of quality, O/H index, degree of saprobity, degree of trophicity, and category based on the phosphatase activity index (PAI) were determined. Our results point to the need for continual monitoring of the water quality in the spring locality

Geographical and biological analysis of the water quality of Moravica spring in the Sokobanjska Moravica drainage basin, Serbia

In this work we performed a geographical analysis of the Moravica spring locality in the Sokobanjska Moravica drainage basin in Serbia, as well as an analysis of the physical, chemical, and biological parameters of the water during a one-year period. The basic sanitary characteristics and physical, chemical, and biological parameters, necessary for understanding locality conditions, were studied, and the saprobity index, class of quality, O/H index, degree of saprobity, degree of trophicity, and category based on the phosphatase activity index (PAI) were determined. Our results point to the need for continual monitoring of the water quality in the spring locality

Seasonal variations of microbiological parameters of water quality of the Velika Morava river Serbia

In this study, we investigated the level of sanitary pollution and organic contamination of the Velika Morava River, the largest river in central Serbia. Samples of water for microbiological analysis were collected at 5 sites, monthly, from April 2010 to February 2011. Sanitary analysis, i.e. enumeration of total and fecal coliforms and intestinal enterococci, indicated moderate to critical fecal contamination, while organic load assessment (oligotroph to heterotroph ratio, index of phosphatase activity) revealed the category of moderately polluted water. We also investigated seasonal variations of these groups of bacteria and the factors that could contribute to these differences. Our results showed that the micro- biological quality of the water in the Velika Morava River during different seasons is affected by numerous factors such as unequal loading of wastewaters, solar irradiation, and relations of flow/dilution and rainfall/runoff. [Acknowledgments. This study was financially supported by the Ministry of Education and Science of the Republic of Serbia: projects No 173025, No 177045 and No 043002.