Papers by Author: Antonio Forn

Abstract: The A357 Al-Si-Mg cast alloy is commonly used for cast production of automotive components in conventional HPDC and in semi-solid processes. The aim of this work is to study the application of A357 cast alloy in thixoextrusion processes. This technology offers new possibilities of application for cast alloys and several advantages in from of conventional processes of hot-extrusion: lower pressure, minor friction forces, higher material fluidity and longer tool life. The thixoextrusion was experimented in a pilot plant, at different speeds and temperatures, with an induction furnace and a 400 Tn press. With ingots of A357 as cast, a tool with a ratio of 8.5 and with temperatures of extrusion around 560 °C, it is possible to obtain extrusion speeds more than 3 m•s-1. In all cases, when the speed of extrusion increases, the press of extrusion decreases. The effect of heat treatments and extrusion speed in the microstructure of the extruded product is evaluated.

Abstract: It is known that ultrasonic waves promote nucleation and globulization of solid particles in aluminium alloys. However, the studies performed up to date have been conducted, in the laboratory, using small volumes of aluminium. This article aims to establish the application of ultrasound effect in the A357 aluminium-silicon alloy in amounts of about 2 kg of material. The experiments have been conducted with different parameters of ultrasonic treatment, evaluating the microstructure of the slurry quenched from the semi-solid state. The globulization effect of aluminium α phase by ultrasounds is very effective in the area close to the ultrasonic horn tip and the transmission system, but its effect highly reduces in the regions far away from the source of ultrasonic waves.

Abstract: Semi solid processing reduces porosity and amount of trapped gas and it allows heat treatment T6 that improves a hard anodized oxide layer. The aim of this work is to show the anodizing possibility of A356 T6 components conformed by Sub-liquidus Casting (SLC) to improve wear and corrosion resistance. This work compares the anodizing effect on tribological properties and corrosion resistance between components obtained by A6061 T6 extruded alloys and from A356 T6 produced by SLC. The effect of rounded silicon crystals on the coating formation and the fracture produced during the coating growth are described.

Abstract: EN AC-46500 aluminium components are formed by Semi-Solid Rheocasting (SSR) in an industrial plant using a 700 tons high pressure machine. The dies wear was designed by the PLCO model of the ProCast simulation software. The components have had a good structural integrity and the mechanical properties after T6 treatment have been equivalent to that obtained by the same alloy by die cast. The present work describes the SSR forming process, the resulting microstructure as well as the optimization of the ageing heat treatment by hardness evolution. The results of the tensile tests make these clear.

Abstract: This work is a contribution to improve the knowledge of components behavior produced by semi-solid processes particularly the Sub-Liquidus-Casting process. Die design was supported by using the Procast simulation program. The effect of the different variables of the process in structural integrity of the product has been described and analyzed. The components were produced using A356 alloy formed on a pilot plant with a 400 Ton THT press. The components study was made by RX, metallographic analysis and mechanical tests. The effects of T5 and T6 heat treatments were also studied.

Abstract: The present work studies the effect the solution heat treatment, during artificial ageing and re-aging, has on the mechanical properties of an A357 aluminium alloy component formed by New Rheocasting. The effect that the evolution of silicon, during the solution treatment at various times, has on the mechanical properties was also examined. The mechanical properties were evaluated performing tensile tests, fractographical analysis and hardness tests. The microstructural characterization was made using optical and electronic microscopy.

Abstract: Anodizing is widely used in the surface treatment of aluminium alloys in order to preserve the integrity of the alloy surface, to minimize the need for maintenance and repair, and to maximize the component life. The aim of this work is to study the influence heat treatments (T5 and T6) have on the anodization of A357 aluminium alloy produced by a Thixocasting process. In particular the effect of shape, size and distribution of silicon and intermetallic phases on the anodic oxide film formation. SEM and EDS analyses were used to examine the microstructural features found on, within and under the anodic oxide layer. Experiments using a tribometer (pin-on-disc tests) were performed in order to evaluate the friction and wear properties of the different layers.

Abstract: This paper describes the heat treatment effect on the eutectic silicon evolution in the A357 alloy, obtained by semisolid forming process (SSM). The coarsening rate of the silicon was determined by Image Analysis Technique in specimens from rheocasting ingots and thixocasting components. The study was realized in the temperature range from 450 to 550°C by applying heating times between 1 and 24 hours. The results show that during the heat treatment the coarsening and sphereodization of the silicon particles is produced and the fragmentation stages, which are observed in conventional alloys, do not appear. Kinetic silicon growth has been adjusted to the Oswald’s ripening equation.

Abstract: Thixocasting or semi-solid casting is an alternative to the traditional casting processes. A numerical simulation of these methods is useful to define the real process. A new test concept will be presented to determine parameters, such as temperature and rates, as well as the die filling and solidification processes. The simulation tools permit us to understand better the processes, to predict and to eliminate potential defects before they take place. The studied component is a steering knuckle made of an A357 aluminium alloy. The microstructure is characterized by optical microscopy. It has been preceded to the development of a model based on the experimental data, it has been defined to the semi-solid as an homogeneous material with thixotropic properties, and the microstructure is a structural parameter. The results are compared with real tests.