M.T. Baile

Effect of Heat Treatments in the Silicon Eutectic Crystal Evolution in Al-Si Alloys

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.

Thixoextrusion of A357 aluminium alloy

The aim of this work is to attempt the application of A357 Al-Si-Mg cast alloy in the thixoextrusion process, evaluating the different forming parameters effect. Thixoextrusion offers several advantages compared with traditional hot-extrusion such as lower pressure, minor friction forces, higher material fluidity and longer tool life. This type of semi-solid process requires high solid fraction (0.7 0.85) is less sensitive to temperature drops and allows more stable material flow at higher speeds. To know the forming parameters that improve the mechanical properties of thixoextruded parts, some extrusion tests were carried out. The results were used as the main criteria for assessing the thixoforming viability of the A357 alloy.

Anodic Oxide Layer Formation on A357 Aluminium Alloy Produced by Thixocasting

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.

Anodizing of A356 T6 Alloys Obtained by Sub-Liquidus Casting

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.

EN AC-46500 Injected by Semi-Solid Rheocasting

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.

Heat Treatments Effect on A357 Components Produced by SSM

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.

Effect of Ultrasounds during the Solidification Process of the A357 Aluminium Alloy

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.