1,721,067 research outputs found
Removal of Pesticides from Water samples by Adsorption whit Fatty Acids supported on Barium Sulphate
Full text linkOleic or linoleic acid supported on barium sulphate was used to remove atrazine and terbuthylazine in the range of 0.1–2.0 μg/L using spiked water samples. The sorption of atrazine depends on the stirring time and the best value is 150 min. Terbuthylazine is removed well with a stirring time of 60 min and its adsorption is about 90%. Detection of the residual pesticide in treated waters, after solid phase extraction (SPE), was carried out by GC‐MS operating in selected ion monitoring (SIM) using a calibration curve by direct injection of standard solutions of herbicide
Influence of trace elements on secondary die-cast aluminium alloys
Full text linkRecycling play a key role on saving of natural resources and on reducing pollution. The recycling of aluminium alloys is also cost-effective, since it reduce the material cost and creates a considerable energy-saving. The use of recycled Al alloys (usually called secondary) has improved in recent years also because of their comparable mechanical properties with primary aluminium alloys.
During the production of secondary aluminium alloys, the scrap are mixed regardless of their specific chemical composition, and then master alloys or pure elements are added to the molten metal. Furthermore, certain impurity elements are either difficult or expensive to remove, and their role in mechanical properties can be important. Due to the presence of these additional trace elements, a number of complex intermetallic phases can therefore form in multi-component Al-Si alloys. Mechanical and physical properties of alloys and castings are strongly related to sizes, morphologies and distribution of these intermetallic phases, which are in turn a function of alloy composition and cooling rate.
The Al–Si based alloys are transversally used in different foundry processes. Among all the technologies, high-pressure die-casting (HPDC) represents the most common process to produce automotive components by secondary Al–Si alloys because it allows one to increase the production by lowering the cycle time and to obtain economically components with complex geometries and high quality surface.
The effects of trace elements and intermetallics phases on features of aluminium castings are still not fully understood, especially when components are made by means of HPDC process. The motivation of the research presented in this doctoral thesis was, therefore, to fill this gap in knowledge. The study has aimed at understanding the influence of various trace elements on the microstructure and mechanical properties of secondary die-cast aluminium alloys and, in particular, on secondary AlSi9Cu3(Fe) die-cast alloys.
A literature review and a sufficient background of previously reported results on the influence of trace elements on the features of aluminium alloys as well as the formation of intermetallic phases were carried out. It was found that the mechanical and microstructural analysis generally referred to primary cast Al alloys with low concentration of trace elements outside of those studied. Furthermore the samples were usually produced on gravity die-cast, while some intermetallics phases were frequently observed in high-pressure die-casting, where higher cooling rates and different feeding conditions exist.
Special attention has been given to:
The effects of Bismuth addition on secondary die-cast aluminium alloys: Bismuth substitute the lead in free-cutting wrought Al alloys, and this is leading to a steady increase of Bi content in secondary Al alloys due to the recycling process.
The nucleation temperature of primary Fe-rich intermetallic compounds, as function of Fe, Mn and Cr content and cooling rate: Fe-rich phases have a high specific gravity and tend to segregate to the bottom of aluminium melts and holding furnaces. These phases form primary solid particles, generally called sludge, thus reduce the effective capacity of the furnace.
The influence of Fe, Mn and Cr addition, separately or in combination, on the microstructural and mechanical characteristics of secondary die-cast aluminium alloys: sludge crystals are hard and brittle compact inclusions which can compromise the machining operations, with a considerable effects on the cutting tool life, and even more degrade the mechanical and physical properties of the component. As recycling of aluminium alloys becomes more common, sludge will be a problem of increasing importance due to the concentration of Fe, Mn and Cr in the scrap cycle
Complessi del rame(II) e del cobalto(II) con coproporfirina-1 e loro caratterizzazione spettrofotometrica
No full textThe influence of Sr, Mg and Cu addition on the microstructural properties of a secondary AlSi9Cu3(Fe) die casting alloy
No full textThe influence of Sr, Mg and Cu content on the microstructure of a high-pressure die cast AlSi9Cu3(Fe) alloy is reported. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes occurring at different Sr, Mg and Cu levels. The results reveal that the Sr and Cu increase the amount of microporosity in the die castings, while Mg counteracts this effect. The secondary dendrite arm spacing and the grain size slightly decrease by the addition of the alloying elements. Compared with the base AlSi9Cu3(Fe) alloy, the Sr-modified alloy shows significant refinement and morphological modification of eutectic Si particles in the central regions of the castings. In contrast, such mechanisms at the casting surfaces are substantially driven by more rapid solidification. The Mg and Cu addition annihilates the benefits of refinement of eutectic Si particles by Sr modification, while it seems to not affect their morphology. The combined addition of Cu and Mg determines an increase of Cu- and Mg-rich intermetallic compounds, while the Sr-modified alloy shows lower fraction of intermetallics, even if comparable to the base alloy in terms of other alloying elements
Effect of Grain Refinement and Cooling Rate on the Microstructure and Mechanical Properties of Secondary Al-Si-Cu Alloys
No full textThe effect of AlTi5B1 grain refinement and different solidification rates on metallurgical and mechanical properties of a secondary AlSi7Cu3Mg alloy is reported. While the Ti content ranges from 0.04 up to 0.225 wt.%, the cooling rate varies between 0.1 and 5.5 C/s. Metallographic and thermal analysis techniques have been used to quantitatively examine the macro- and microstructural changes occurring with grain refiner addition at various cooling rates. The results indicate that a small AlTi5B1 addition produces the greatest refinement, while no significant reduction of grain size is obtained with a great amount of grain refiner. On increasing the cooling rate, a lower amount of AlTi5B1 master alloy is necessary to produce a uniform grain size throughout the casting. The combined addition of AlTi5B1 and Sr does not produce any reciprocal interaction or effect on primary a-Al and eutectic solidification. The grain refinement improves the plastic behavior of the alloy and increases the reliability of castings, as evidenced by the Weibull statistics
Effects of chromium and bismuth on secondary aluminium foundry alloys
No full textThe effects of impurities such as Chromium and Bismuth on the microstructure and mechanical properties of an AlSi9Cu3(Fe) secondary diecasting alloy are investigated. Metallographic and image analysis techniques have been used to examine the microstructural changes. The results indicate that the area fraction and the size of brittle α-Alx(Fe,Mn,Cr)ySiz intermetallic compounds increase by increasing the Cr content, and this affects the ultimate tensile strength and the ductility of the alloy at higher Cr level. On the other hand, the Bi addition seems to not produce significantly changes in the microstructure and in the average mechanical properties of the secondary AlSi9Cu3(Fe) alloy. However, the Weibull statistics show that the addition of Bi leads to less reliable castings, which may be associated with an increase of oxide film defects
Trace alloying elements in secondary aluminium alloys
No full textSecondary aluminium and alloys are getting wide acceptance world-wide since recycling process requires lower potential energy than primary aluminium production. The control of type and amount of trace elements during recycling operations can be either difficult and expensive. Furthermore, the role of trace elements in foundry metallurgy is not fully understood, even if it is sometimes a tool actually used to manipulate the microstructure of the alloys. Trace elements can be beneficial, as well as detrimental to the structure and properties of the alloy.
Effects of Chromium and Bismuth additions to an AlSi9Cu3(Fe) secondary diecasting alloy on the microstructure and mechanical properties are investigated. The results indicate that the area fraction and the size of α-Alx(Fe,Mn,Cr)ySiz intermetallic compounds increases by increasing the Cr content, and this affects the ultimate tensile strength and the ductility of the alloy at the highest Cr level. Contrary, the Bi addition seems to not produce significantly changes in the microstructure and mechanical properties of the recycled AlSi9Cu3(Fe) alloy
Evolution of sludge particles in secondary die-cast aluminum alloys as function of Fe, Mn and Cr contents
No full textThe evolution of sludge particles in a secondary high-pressure die-cast AlSi9Cu3(Fe) alloy has been investigated over three levels of iron (0.80, 1.00, 1.20 wt.%) and manganese (0.25, 0.40, 0.55 wt.%), and two levels of chromium (0.06, 0.10 wt.%). Metallographic and image analysis techniques have been used in order to quantitatively evaluate the morphological and dimensional variations of sludge with different Fe, Mn and Cr contents. The results indicate that any increase of the Fe, Mn and Cr level promotes the formation of coarser sludge, with polyhedral and star-like morphologies. Fe and Mn produce an increase on the number of primary Fe-rich particles, while Cr promotes the formation of a large number of secondary Fe-rich particles. No relationship is revealed between the morphological variation of sludge and the Fe, Mn or Cr contents, as well as between the sludge factor and the Fe:Mn ratio. In the analyzed range of composition, the design of experiment methodology and the analysis of variance have been used in order to develop statistical models that accurately predict the average size and number of sludge particles in the AlSi9Cu3(Fe) diecasting alloys
Influence of Sludge Particles on the Tensile Properties of Die-Cast Secondary Aluminum Alloys
No full textThe effects of sludge intermetallic particles on the mechanical properties of a secondary AlSi9Cu3(Fe) die-casting alloy have been studied. Different alloys have been produced by systematically varying the Fe, Mn, and Cr contents within the composition tolerance limits of the standard EN AC-46000 alloy. The microstructure shows primary α-Alx(Fe,Mn,Cr)ySiz sludge particles, with polyhedral and star-like morphologies, although the presence of primary β-Al5FeSi phase is also observed at the highest Fe:Mn ratio. The volume fraction of primary compounds increases as the Fe, Mn, and Cr contents increase and this can be accurately predicts from the Sludge Factor by a linear relationship. The sludge amount seems to not influence the size and the content of porosity in the die-cast material. Furthermore, the sludge factor is not a reliable parameter to describe the mechanical properties of the die-cast AlSi9Cu3(Fe) alloy, because this value does not consider the mutual interaction between the elements. In the analyzed range of composition, the design of experiment methodology and the analysis of variance have been used in order to develop a semi-empirical model that accurately predicts the mechanical properties of the die-cast AlSi9Cu3(Fe) alloys as function of Fe, Mn, and Cr concentrations
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