Effect of Phosphorus and Strontium Additions on Formation Temperature and Nucleation Density of Primary Silicon in Al-19 Wt Pct Si Alloy and Their Effect on Eutectic Temperature

The influence of P and Sr additions on the formation temperature and nucleation density of primary silicon in Al-19 wt pct Si alloy has been determined, for small volumes of melt solidified at cooling rates _T of ~0.3 and 1 K/s. The proportion of ingot featuring primary silicon decreased progressively with increased Sr addition, which also markedly reduced the temperature for first formation of primary silicon and the number of primary silicon particles per unit volume �Nv: When combined with previously published results, the effects of amount of P addition and cooling rate on �Nv are in reasonable accord with �Nv� _T ¼ ðp=6fÞ1=2 109 [250 � 215 (wt pct P)0.17]�3, where �Nv is in mm�3, _T is in K/s, and f is volume fraction of primary silicon. Increased P addition reduces the eutectic temperature, while increased Sr appears to generate a minimum in eutectic temperature at about 100 ppmw Sr

Thermochemical synthesis of nanostructured Cu-Al2O3 composite powder

Synthesis of Cu-Al2O3 nanocomposite powder through a thermochemical method from the water solution of copper nitrate (Cu (NO3)2.3H2O) and aluminum nitrate (Al (NO3)6.9H2O) is studied in this research. X-ray diffraction (XRD) technique, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the synthesized powder. XRD results show that γ-Al2O3 phase begins to form at the temperature ≈800°C during the heat treatment process. Studying SEM micrographs proves that the nano sized Al2O3 particles are homogenously dispersed in the copper matrix. XRD results also show that disappearing the reflects of CuO peaks after performing a reduction chemical reaction at the temperatures above 800°C in hydrogen atmosphere indicates that such chemical reaction at the temperatures above 800°C is required in order to achieve Cu-Al2O3 nanocomposite powder

On the capability of grain refinement during selective laser melting of AlSi10Mg alloy

This work focuses on the origin and capability of grain refinement in the microstructure of selective laser-melted AlSi10Mg alloy. The grains in printed microstructure have been oriented in a random manner and there is no sign of preferred micro-texture. In the molten pool, columnar grains have been formed aligned with the building direction, and stretched toward the center of the molten pool. The fraction of refined equiaxed grains by the size of fewer than 10 μm is considerable (∼40%) which have been formed (i) during solidification owing to high solidification rate to thermal gradient ratio, or due to (ii) the occurrence of dynamic recrystallization during the manufacturing process after completion of the solidification. These refined equiaxed grains have been differentiated through plotting Grain Orientation Spread maps. The numerous thermal cycles experienced by each layer cause considerable tensile or compressive micro-plastic strains and give rise to dynamic recrystallization. The presence of incomplete grains can be clearly traced which are ready to be evolved into the recrystallized grains. This, besides the extensive substructure development and sub-grain formation, are main proof for governing of continuous mechanisms of recrystallization mechanisms. Finally, selective laser melting has been approached as a thermomechanical processing route, and the calculated micro-plastic strain has been compared with a critical strain of dynamic recrystallization obtained from the hot compression testing method

Optimisation of the strength of aluminium foam sandwich AFS panel by different heat treatments

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Influence of pre-oxidation of NiAl intermetallic particles on thermal stability of Al/NiAlp composites at 500 °C

Thermal stability of PM Al/5%NiAl composites has been studied by exposure at 500 °C up to 24 h. NiAl intermetallic particles were employed as-received and after pre-oxidation at several temperatures. The optimal oxidation condition was determined based on its ability to delay interfacial reactions and prevent debonding at the metal/reinforcement interfaceFinancial support of the Spanish Ministry of Education and Science, project CICYT MAT2003-00722, is gratefully acknowledged. Thanks are also due to J.L. González-Carrasco for helpful discussion. H.A.P. acknowledges the Iranian Ministry of Science, Research and Technology for a scholarshipPeer reviewe

Assessment of tensile behaviour of an Al–Mg alloy composite reinforced with NiAl and oxidized NiAl powder particles helped by nanoindentation

AA5056 matrix composites have been reinforced with as-received and oxidizedNiAlparticles and their nanohardness investigated as a function of distance to reinforcement. Results indicate that a non-heat treatable aluminium matrix, as is the present case, does not require that the intermetallic particles are surrounding by a protective Al2O3 layer to avoid reactions at matrix-reinforcement interfaces. On the other hand, the quality of the matrix-reinforcement bonding has been quantified by the reinforcement influence distance, defined as the distance from the particle at which the nanohardness of the matrix drops to its asymptotic valueFinancial support of Spanish Ministry of Education and Science, Projects CICYT MAT2003-00722, MAT2003-04931-C02-02 and MAT2006-01251, is greatly acknowledged. H.A.P. acknowledges the Iranian Ministry of Science, Research and Technology for a scholarshipPeer reviewe

Iron-rich intermetallic phases and their role in casting defect formation in hypoeutectic Al-Si alloys

Iron is the most common and detrimental impurity in aluminum casting alloys and has long been associated with an increase in casting defects. While the negative effects of iron are clear, the mechanism involved is not fully understood. It is generally believed to be associated with the formation of Fe-rich intermetallic phases. Many factors, including alloy composition, melt superheating, Sr modification, cooling, rate, and oxide bifilms, could play a role. In the present investigation, the interactions between iron and each individual element commonly present in aluminum casting alloys, were investigated using a combination of thermal analysis and interrupted quenching tests. The Fe-rich intermetallic phases were characterized using optical microscope, scanning electron microscope, and electron probe microanalysis (EPMA), and the results were compared with the predictions by Thermocalc. It was found that increasing the iron content changes the precipitation sequence of the beta phase, leading to the precipitation of coarse binary beta platelets at a higher temperature. In contrast, manganese, silicon, and strontium appear to suppress the coarse binary beta platelets, and Mn further promotes the formation of a more compact and less harmful a phase. They are therefore expected to reduce the negative effects of the phase. While reported in the literature, no effect of P on the amount of beta platelets was observed. Finally, attempts are made to correlate the Fe-rich intermetallic phases to the formation of casting defects. The role of the beta phase as a nucleation site for eutectic Si and the role of the oxide bifilms and AIP as a heterogeneous substrate of Fe intermetallics are also discussed

Structural characterization and magnetoimpedance effect in amorphous and nanocrystalline AlGe substituted FeSiBNbCu ribbons

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