I. Alfonso

Hardness-lattice parameter correlation for aged Al-Zn-Mg alloys

Two ternary Al-2.2Zn-0.95Mg and AI-5.5Zn-2.1Mg (in wt pct) alloys, with Zn:Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500°C for 0.5 h and aged at 180°C for times between 0.5 and 80 h. The structural characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and Vickers microhardness measurements (HV). The study was focused on the investigation of the precipitates formation and the relationship between hardness and lattice parameter for α-Al. The results showed that there was an inverse correlation for all the experimental conditions, and the aged peaks coincided with lattice parameter minima. Significant precipitates formation only occurred for the alloy containing 5.5 wt pet Zn and 2.1 wt pet Mg, provoking an important strengthening and variations in the lattice parameter, however, this was not observed for the alloy containing 2.2 wt pet Zn and 0.95 wt pet Mg. A plausible explanation of the increment of hardness values could be the presence of a well distributed η phase (MgZn 2 ). At initial stages of the precipitation process, η′ was the most abundant precipitate while the phase τ was observed at overaged conditions. These results showed that the aging response of the conventionally cast Al-Zn-Mg alloys could be obtained using the lattice parameter of the α-AI matrix, even for alloy systems with low precipitates formation.

Fractal analysis of the heat treatment response for multiphase Al alloys

The present work shows the fractal analysis for the microstructure of Al-6Si-3Cu-xMg (x = 0.59, 3.80 and 6.78 wt.%) alloys, solution heat treated at 480 °C for times ranging from 4 to 72 h. Microstructural changes were examined using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), and quantified by measuring conventional characteristics of second phases. The fractal analysis of the microstructures was also carried out using fractal dimension (Df). Results shown important variations in the microstructure when Mg content is increased, being the eutectic Al-Si and Cu-rich phases the predominant phases for the alloys with low Mg content, while for higher Mg contents predominant phases were Mg2Si and Cu-rich phases. The analysis of Df showed that this parameter could be used in order to compare the microstructural solution response of the Al alloys. Besides, it was possible to correlate the fractal dimension with the shape factor of the second phases, mainly for the alloys with only one second phase remaining after heat treatment.

Potencialidades computacionales del Método de los Elementos Finitos para la modelación y simulación de materiales compuestos: revisión

This work presents a review of computational models that use the Finite Elements Method (FEM) for the study of composite materials mechanical behavior, focusing the analysis in materials reinforced by particles or fibers. Bibliographic analysis shows that using FEM it is possible to successfully estimate the effect on the composites mechanical properties, of parameters such as the reinforcement type, volumetric fraction, orientation, aspect ratio and size. This review showed that the most studied property is Young´s modulus, as well as the models that favor the geometry decrease using the computational advantages. Future work that needs attention is addressed.

Synthesis, characterization, and heavy metal adsorption properties of sulfonated aromatic polyamides:

This work reports on the synthesis of a series of new sulfonated fluorine-containing aromatic polyamides with increasing degree of sulfonation (DS). The chemical structure of the resulting polymers was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (1H NMR) which evidenced the presence of amide and sulfonic groups in the proposed concentrations. Afterwards, we carried out a comparative study of heavy metal ion adsorption in membranes based on these aromatic polyamides. The main purpose was to determine the adsorption capacity of the prepared polymer membranes toward Pb2+ and Hg2+ in aqueous media at 30°C and pH neutral. The adsorption kinetics was evaluated with the pseudo-first-order and pseudo-second-order models. The adsorption kinetics in all the polyamide membranes followed the pseudo-second-order rate law for both heavy metal ions. It is observed that the adsorption capacities of all the polyamides toward Pb2+ ions are higher than those of the Hg2+ ions, and these capacities increase as the DS increases. The equilibrium adsorption amounts, q e, were 11.87 mg/g for Pb2+ and 5.17 mg/g for Hg2+ ions for the highest sulfonated polymer.

Study on the structural and magnetic properties of Ru 1−x Mo x Sr 2 GdCu 2 O 8±z system

The structural and magnetic properties of Ru_1-xMo_xSr₂GdCu₂O₈ with 0.0 ≤ x ≤ 0.50 were investigated through Mo substitution in the Ru sites. Samples were synthesized by solid-state reaction at ambient pressure at temperature between 960 °C and 1060 °C. X-ray diffraction results indicate that the partial substitution of Ru by Mo within the studied level of doping takes place isostructurally in a tetragonal structure (space group P4/mmm) with a solubility up to x = 0.50. Rietlveld- refinement analysis indicates that the Cu-O(2) and Ru-O(3) bond lengths increase with Mo content, while the Cu-O(1) and Ru-O(1) bond lengths, as well as Cu-O(1)-Ru bond angles decrease with increasing x with a minimum at approximately x = 0.30, and then increase for x > 0.30 resulting in inverse bell-type curves. Results of the DC magnetic susceptibility measurements on samples indicate that all samples exhibit ferromagnetic ordering, with T^Curie values depend on Mo content with a dependence that seems to be similar to Cu-O(1)-Ru bond angle. These results suggest a relationship between the structural and magnetic properties in the Ru_1-xMo_xSr₂GdCu₂O₈ system.

Efecto de las variables experimentales sobre la microdureza en aleaciones Al-6Si-3Cu-xMg T6

Three Al-6Si-3Cu-xMg (x = 0.59, 3.80 and 6.78 wt. %) alloys were produced using conventional ingot casting metallurgy and melt-spinning. The study was focused to investigate the effect of Magnesium content and aging time ant temperature on precipitates and microhardness. Obtained alloys were solution heat treated at 480 oC for 12 h and aged at 150, 180 and 210 °C for times between 0.05 and 100 h. Multifactorial designs were used, summarized in the dependency: VHN= f (t, T, %Mg), where VHN is Vickers microhardness, t is aging time and T is aging temperature. Transmission Electron Microscopy and microhardness techniques were used. Results shown variations in precipitates composition: CuAl2 needles for the alloys with 0.59% Mg and Q (Al5Cu2Mg8Si6) with irregular shapes, for the alloys with 3.80 and 6.78% Mg. For melt-spinning alloys, temperature originates the most significant variation on microhardness, followed by Mg content and aging time. The increase of Mg content originates greater microhardnesses. For conventionally cast alloys temperature is the only factor that significantly changes microhardness.