Christian Sánchez

This article investigated the influence of copper (Cu) and nickel (Ni) on atmospheric corrosion in gray cast iron under simulated marine conditions. The goal was to compare the effect of Cu and Ni addition in castings with weathering steels. Selected alloys were cast, cut, prepared, and heat-treated for microstructure homogenization. Accelerated corrosion tests were conducted using a salt spray chamber. Corroded samples were analyzed for corrosion thickness and deposits using scanning electron microscopy, X-ray diffraction, and electrochemical techniques. The results indicate that alloying elements significantly affect corrosion processes. In the long-term, Cu had a greater impact on the corrosion mechanisms than Ni. Both Cu and Ni exhibited similar effects on the corrosion mechanisms in gray cast iron and weathering steels. In the initial and final stages, the behavior was comparable to that of weathering steels, but in the intermediate stage, it differed from the literature, suggesting the presence of an additional mechanism between these stages.

The microstructure of the coating during hot-dip galvanizing under industrial conditions of two structural steels, a low-silicon ASTM A36 steel and a high-silicon Q345B steel, both of commercial grade, have been characterized for industrial-relevant times. In both cases, it is noted that the formation of the Fe–Zn phases begins in the early stages in the heating step of the steel, a situation in which all the phases are in the solid state. These last observations have been taken into consideration and the microstructures of short times are analyzed, showing that the effect of silicon is present at longer times. The characterization was carried out through traditional metallographic techniques including SEM-EDS and XRD equipment. The evolution in time of the microstructure of both steels is examined, being able to observe that the mechanism by which silicon accelerates the formation of Fe–Zn phases in galvanizing is related to the presence of the liquid phase in contact with the ζ layer formed in earlier times, accumulating silicon in the ζ–liquid interphase. These results are directing the analysis towards proposing the hypothesis of a mechanism of penetration of the liquid phase through ζ–ζ boundaries by variations in the surface free energies that allow the penetration of the liquid phase according to the Gibbs Smith condition. Finally, the observations provided us with a deeper understanding of the phase evolution in the hot-dip galvanizing of high silicon steels.

The microstructure of the coating during hot-dip galvanizing under industrial conditions of two structural steels, a low-silicon ASTM A36 steel and a high-silicon Q345B steel, both of commercial quality, have been characterized for industrial-relevant times. For both cases it is noted that the formation of the Fe-Zn phases begins in early stages during the heating of the steel, a situation in which all the phases are in the solid state. The characterization was carried out through traditional metallographic techniques including SEM-EDS and DRX equipment. The evolution in time of the microstructure of both steels is examined, being able to observe that the mechanism by which silicon accelerates the formation of Fe-Zn phases in galvanizing is related to the change in the energy of the interfaces caused by a silicon accumulation in the liquid phase in contact with the ζ layer. These results provided us with a deeper understanding of the phase evolution in the hot-dip galvanizing of high silicon steels.

The effect of the application of forced convection during the continuous solidification of Al-Si alloys has been presented in this work. The investigation has been made on the hypothesis that as an alloy solidifies under the action of a rotating magnetic field, a nondendritic casting structure would be obtained. The Al-Si alloy has been studied in its three different states (original, modified, and modified with a grain refiner), using a magnetic stirring equipment with permanent magnets, a device that has allowed the study of the effect of the rotational speed (degree of stirring) on the micro- and macro- solidification structure, as well as on the material’s mechanical properties. With the purpose of validating the hypothesis, different analyses and tests have been carried out, such as thermal analysis of the solidification process, micro- and macrostructural analysis, and hardness measurements for the different process conditions studied. The results have shown that magnetic stirring affects the cooling curves, expanding the solidification range. A microstructural evolution of the alloys has also been observed, from a 100% dendritic structure to a mature rosette type structure, in addition to a notable decreasing of grain size, which results in the improvement of the material’s mechanical behavior.

Firmness at 5 °C, dynamic viscoelastic moduli (G' G) and capillary extrusion profiles at 20 °C, were obtained on double cream cheese after the different steps of processing (curd obtention, mixing at 70 °C and 500 r.p.m. with heat‐denatured WPC, heating at 85 °C, homogenizing at 20 MPa (1st stage) and 5 MPa (2nd stage) and cooling to 20 °C and 13 °C) and storage 7–9 days at 5 °C. It was found that double cream cheese became firmer and more elastic after heating and homogenization, although it became softer and more viscous after mixing and cooling. Transmission Electron Microscopy (TEM) and cryo‐Scanning Electron Microscopy (SEM) micrographs showed that rheology results could be related to aggregation (during heating and homogenization) and disruption (during cooling) of milk fat globule/casein complexes. Dispersion of homogenization clusters after cooling, and aggregation of milk fat globules during storage caused double cream cheese structural instability to appear. It was suggested that the heterogeneity of capillary extrusion profiles could be quantified through application of fractal concepts and Fourier analysis and related to structure and texture of double cream cheese.