Papers by Author: Claudemiro Bolfarini

Abstract: Rapid solidification processes, RSP, are powerful tools to induce microstructural modifications, which may improve mechanical properties of alloys. In this paper the influence of rapid solidification on the formation of the undesirable brittle intermetallic compounds promoted by Si and Fe in Al-6Si-3Cu (A319-type) alloy have been investigated. The alloy have been casted using both conventional method and water-cooled wedge-copper mould. The microstructures have been evaluated by using a combination of X-ray diffraction, optical, scanning and transmission electron microscopy, and by Vickers microhardness. By increasing the cooling rate the length of the intermetallic β-Al5FeSi phase decreased, accompanying the same tendency of the secondary dendritic arm spacing. These results are accompanied by an increasing in hardness. Moreover, the formation and growth of the Al2Cu phase have been suppressed. These microstructural and hardness changes with the rapid solidification might be attributed to the increased solid solution content of the elements in the Al matrix.

Abstract: Nanostructured aluminium-based alloys are light yet much stronger than conventional materials, which offer technological opportunities for applications such as in aerospace industry. One of the alloys of great interest for such applications is based on Al-Cu system and one of the main challenges for development of such alloys are associated with powder processing. However, processing such powder alloys into bulk material requires relatively low temperature and high pressure, which presents significant processing difficulties. A two-step approach is being explored in our group to reach the goal of a fully dense bulk material. Firstly, cold pressing is used to partially consolidate the powder material and secondly, hot extrusion is used to consolidate the alloy to full density. Process modelling is being used to design the extrusion process, including the extrusion ratio and extrusion length, to limit the temperature increase during extrusion as a result of adiabatic heating, and to avoid excessive heating to limit the undesirable grain growth of the material. A parametric study of extrusion parameters is presented and processing parameters are recommended. The use of process modelling has proven to be a useful tool in understanding the results from the extrusion experiments and limiting the number of interactions during extrusion.

Abstract: A nanostructured aluminium alloy powder, prepared by rapid solidification via gas atomization, was consolidated into bulk material under various processing conditions via hot extrusion. The microstructure modifications and mechanical properties of the consolidated alloys as a function of the extrusion conditions were investigated. The increase in the extrusion-load with the increase of extrusion-rate and decrease of temperature are shown and discussed in association with the modification in the microstructures. The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion parameters. Furthermore, suggestions are given for rationalising the extrusion ratio and temperature conditions for the consolidation of nanostructured aluminium alloy powders via hot extrusion.

Abstract: Deposits of the Fe-6.5wt%Si alloy produced by spray forming were annealed at temperatures between 900 and 1300oC, during 1h in vacuum and quenched in oil at temperatures between 300 and 700oC, separately. Magnetic properties, singular microstructure and random crystallographic texture were measured. After annealing at 1250°C for 1h under vacuum, the average grain size is of 500 μm, the grain orientation is random and the magnetic properties were: power loss of 1.30 W/kg, maximum permeability of 15400 and coercive force of 40 A/m, at B=1 T, f=60 Hz by using 0.60 mm thick rings for all studied samples. Higher annealing temperatures cause no decreasing of these properties. After quenched at 700°C, an improvement the magnetic properties where detected due to antiphase domain B2 growth. The magnetic properties were: power loss of 1.59 W/kg, maximum permeability of 12300 and coercive force of 76 A/m, at B=1 T, f=60 Hz.