This work analyzes the effect of Cu additions on the microstructure of quaternary alloys Al-6Si-7Mg-xCu (x= 3, 5 and 7 wt.%) produced by conventional metallurgy. Microstructural modifications were studied using Optical Microscopy (OM), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), focusing on second phases identification and quantification. Conventional image analyses were developed measuring the total percentage of second phases, and individually for each phase determining its equivalent diameter, shape factor, roundness and aspect ratio; while fractal analyses were carried out complementarily through fractal dimension measurements for the whole microstructure and for individual phases. Compression tests were also carried out. SEM and XRD results revealed that second phases were eutectic Si, Mg2Si, Al2Cu and Al5Cu2Mg8Si6 (Q). The increase in Cu content led to higher quantities of these phases, mainly Al2Cu, which was barely present for the alloy with the lowest Cu content. Morphologies of second phases depended on Cu content, being present as eutectic, block like, finely dispersed or primary particles. The combination of conventional and fractal parameters provided a useful tool for comparatively analyze microstructural modifications and second phases features. It was also found that the compressive behavior of the alloys depended on the resulting microstructures.

ABSTRACT The aim of this work is to increase the abrasive wear resistance of a coating, applied on plates of AISI 1020 carbon steel, using tubular coated electrodes with the Fe-Cr-Mn-C alloy system. In order to achieve this increase, V was added to the alloy system. The resulting coating were studied using optical microscopy (MO), X-ray diffraction and microhardness tests. Wear tests were carried out in accordance with the procedure of ASTM G 65-B. Results showed that the addition of V to the Fe-Cr-Mn-C system caused significant microstructural modifications, decreasing the amount of martensite in the coating, and increasing the dimensions of the eutectic zone. Also, V originated the formation of VC, in addition to the Cr7C3 carbides present for the two alloy systems. These microstructural modifications provoked that coatings deposited using the Fe-Cr-Mn-V-C alloy system show a significantly higher abrasive wear resistance.

RESUMEN El presente trabajo persigue incrementar la resistencia al desgaste abrasivo de un revestimiento, aplicado sobre placas de acero al carbono del tipo AISI 1020, utilizando electrodos tubulares revestidos con el sistema de aleación Fe-Cr-Mn-C. Con la finalidad de lograr este incremento, al sistema de aleación se le adicionó V. Los depósitos resultantes se estudiaron mediante microscopía óptica (MO), difracción de rayos-X y ensayos de microdureza. Los ensayos de resistencia al desgaste por abrasión se llevaron a cabo en acuerdo con el procedimiento la norma ASTM G 65-B. Los resultados mostraron que la adición de V al sistema Fe-Cr-Mn-C originó modificaciones microestructurales significativas, disminuyendo la cantidad de martensita en el depósito, y aumentando el tamaño de la zona eutéctica. Asimismo, el V originó la formación de VC, además de los carburos Cr7C3 presentes para los dos sistemas de aleación. Estas modificaciones microestructurales causaron que los depósitos que utilizan el sistema de aleación Fe-Cr-Mn-V-C presenten una resistencia al desgaste abrasivo significativamente mayor.

Abstract: Fe-Mn-C (Hadfield) alloys for surfacing weld deposits have demonstrated excellent wear resistance under high dynamic loads. In recent years, numerous studies have been conducted to improve their wear resistance and performance through the introduction of others alloying elements. In the present work, microstructure and hardness of high Mn surfacing welds with 1.2% V and 2.4% Si additions were investigated. The surfacing welds were deposited using experimental tubular coated electrodes. Phases and micro constituents in the resulting deposits were identified using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness and micro hardness. Based on the obtained results, V additions to the alloy led to the formation of austenite as predominant phase. Besides, contributed to the formation of vanadium carbides (VC), without the presence of complex carbides. Otherwise, Si addition favored the formation of an interdendritical ferrite network. The addition of these elements favored the increase in the properties of the weld deposits, potentializing their use in applications that require high wear resistance under high loads.

Resumen: Las aleaciones para el relleno superficial Fe-Mn-C (Hadfield) han demostrado una excelente resistencia al desgaste bajo altas cargas dinámicas. En los últimos años se han realizado numerosos estudios para aumentar la resistencia al desgaste y mejorar su desempeño, a través de la introducción de otros elementos de aleación. En el presente trabajo se investiga la microestructura y dureza de los depósitos de relleno con alto contenido de Mn y adiciones de 1.2% de V y 2.4% de Si. Los depósitos estudiados se realizaron utilizando electrodos tubulares revestidos fabricados a escala de laboratorio. Las fases y microconstituyentes en el metal depositado se identificaron mediante microscopía óptica (MO), electrónica de barrido (MEB), difracción de rayos X (DRX), dureza y microdureza. De acuerdo a los resultados obtenidos, la adición de V al sistema aleante originó que la fase predominante fuera la austenita. Además, contribuyó a la formación de carburos de vanadio (VC) en la microestructura de la capa de relleno, sin observarse la presencia de carburos complejos. Por otra parte, la presencia de Si favoreció la formación de una red de ferrita interdendrítica. La adición de estos elementos de aleación mejoró las propiedades de estos depósitos, potencializando su uso en aplicaciones que requieren alta resistencia al desgaste bajo altas cargas.

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.

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.

En este trabajo se presenta una revisión bibliográfica de modelos computacionales que utilizan el Método de los Elementos Finitos (MEF) para el estudio del comportamiento mecánico de los materiales compuestos, enfocándose el análisis en materiales reforzados por partículas o fibras. El análisis realizado muestra que el MEF permite estimar, de manera efectiva, la influencia sobre las propiedades mecánicas de los materiales compuestos, de factores como el reforzante, su fracción volumétrica, orientación, relación de aspecto y tamaño. Esta revisión mostró que la propiedad más estudiada es el módulo de Young, así como los modelos que favorecen la disminución de la geometría utilizando las ventajas computacionales. Se destaca el trabajo futuro que requiere atención.