Materials In Semi-solid State Research Articles

Influence of semisolid squeeze casting technology on alpha phase and eutectic of AlSi7Mg0.3

The paper deals with processing of material in semisolid state by the technology of semisolid squeeze casting. The investigated material was a subeutectic aluminium alloy AlSi7Mg0.3. The influence of various preparation meth-ods of batch material on the structure after processing by this technology was studied. Alloy AlSi7Mg0.3 was pre-pared as gravity cast, inoculated, heat treated and by technology of direct squeeze casting. In article is assessed microstructure of castings before and after processing by technology of semisolid squeeze casting. The shape and distribution of eutectic silicon was observed. The shape and the distribution of alpha phase formations has an im-pact on whether micro-volumes of molten eutectic will be closed in alpha phase or will be segregated along the boundaries of alpha phase formations. It was observed the partial inheritance in microstructure. Also the segrega-tion in surface layer was observed.

DESARROLLO DEL PROCESO TIXO FORJADO LATERAL PARA LA FABRICACIÓN DE ESTRUCTURAS HÍBRIDAS ACERO-ALUMINIO

El acero y las aleaciones de aluminio son algunos de los materiales mas importantes en la industria del automovil debido a sus buenas propiedades. La union de ambos materiales permite la creacion de nuevas estructuras hibridas que combinan la dureza y resistencia al desgaste de los aceros con la baja densidad de las aleaciones de aluminio. Sin embargo, debido a las propiedades fisicas y mecanicas dispares de estos metales, es dificil obtener uniones metalurgicas con metodos de soldadura tradicionales. Estas diferencias en las propiedades conducen a la formacion de compuestos intermetalicos (IMC) en la intercara que por su naturaleza dura y fragil resultan perjudiciales para su aplicacion final. La produccion de estructuras hibridas mediante tixoconformado de aluminio sobre acero en un unico paso es un proceso prometedor para la fabricacion de componentes funcionales con buenas propiedades mecanicas. Este proceso permite unir materiales disimilares en estado semisolido, de forma que la union de los materiales ocurre a una temperatura inferior que en los metodos tradicionales de soldadura, provocando una disminucion del espesor de la capa intermetalica. En el presente trabajo, se ha fabricado un componente real de automocion llamado brazo de la cuna delantera en la aleacion de aluminio A356 y unido a un tubo de acero de calidad S355JH2. El conformado y la union de los metales se ha realizado en un solo paso por el proceso de tixo forja lateral. Para determinar la calidad de la pieza asi como la bondad de la union se ha llevado a cabo un analisis mecanico y metalografico cualitativo. Los resultados han revelado que es posible fabricar los componentes hibridos de calidad en cuanto a la union intermetalica aunque se hace necesario un pequeno rediseno geometrico para reducir tensiones locales. Palabras clave: Estructuras hibridas acero-aluminio, Semisolido, union, fase intermetalica, tixoconformado, ligero.

Complex shape metallic glass composites produced in one step by mini-thixoforming

Mini-thixoforming is a technique based on forming in semi-solid state: the material becomes partially melted, retains a fraction of solid phase and is able to fill intricate cavities in a single forming step. In this study, metallic glass composites were produced by a combination of powder metallurgy and processing of material in semi-solid state. The experimental program was composed of processing mechanically compressed powder in semi-solid state. The powder mixture consisting of iron powder + metallic glass powder. Metallic glass was obtained in the form of a rod and prior to semi-solid processing was characterized by scanning electron microscopy (SEM), light microscopy and micro-hardness test. The rod was milled and obtained powder was mixed with Fe powder. In order to achieve a better compaction, the mixture was mechanically compressed before heating to a semi-solid state. After the semi-solid processing was carried out, homogenous composites reinforced with Fe powder were obtained. Characterization of the produced structures and comparison of final structures at different temperatures were carried out again by DTA-TG, XRD, SEM-EDX, light microscopy and micro-hardness test, and the analysis results of composite structures have been compared with the initial ones. It was concluded that one step formation process of compact composite was successfully completed.

Modelling and Simulation of Die Casting Process for A356 Semi-solid Alloy

To describe the flow behaviors of semi-solid state alloy A356, two non-Newtonian constitutive equations are modeled in this paper. All the parameters in the above equations are obtained by an isothermal shear experiment. The CFD software PROCAST is used to simulate the process of die filling. The filling temperature is 585 oC (solid fraction is 0.4). A Newtonian type fluid which stands for the traditional casting is also performed. Based on the results of the simulation, it is found that the material in semi-solid state exhibits an apparently higher viscosity and thus, flows much more smoothly than the Newtonian fluid. In addition, the semi-solid metal alloy has a special die filling behavior compared with liquid filling which is of great importance in improving the quality of the final components.

Thixo-forging and simulation of complex parts of aluminum alloy AlSi7Mg

In order to investigate the formability of metal material in semisolid state, a series of experiments were carried out by thixo-forging the complex part of aluminum alloy AlSi7Mg. Through changing the upper punch, aluminum parts with different upper-cup dimensions can be successfully produced. The numerical simulation was conducted for investigating the forming limits of AlSi7Mg during thixo-forging. It is found that the simulation result is in good agreement with the experiment one.