M.M. Peres

Hot Extrusion of Nanostructured Al Alloy Powder: Extrusion Ratio and Temperature Effect on the Microstructure and Mechanical Properties

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.

2Mg-Fe Alloy Processed by Hot Extrusion: Influence of Particle Size and Extrusion Reduction Ratio on Hydrogenation Properties

Samples of a 2Mg-Fe (at.%) mixture were produced by high energy ball-milling (HEBM) with ball to powder ratio = 20:1, in an argon gas atmosphere, in 190 ml vials (sample-1) to produce powders and in 300 ml vials (sample-2) to produce plates. Both samples were cold-pressed into preforms. The preforms were then extruded at 300°C at a ram speed of 1mm/min., with the following extrusion ratios: sample-1 at 3/1 to ensure porosity and sample-2 at 5/1 to increase the adhesion of the plates. The resulting bulks from samples 1 and 2 were hydrogenated for 24h in a reactor under 15 bar of H2 to produce the Mg2FeH6 complex hydride, and at 11 bar of H2 to produce both the complex hydride and MgH2 hydride. In addition, sample-1 was severely temperature-hydrogen cycled to verify its microstructural stability and the influence of grain size on the sorption properties. XRD patterns showed Mg(hc), Fe(ccc) and Mg2FeH6 in both samples, and sample-2 also contained MgH2 and MgO (attributed to processing contamination). DSC results demonstrated that the initial desorption temperature of sample-1 was lower than that of sample-2. However, sample-2 showed faster desorption kinetics, presenting a desorption peak about 73°C below that of sample-1. This could be attributed to the activation/catalyst effect of the MgH2 hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.

Processing and Simulation for Consolidation of Nanostructured Al-Cu Powder Alloys

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.

Processing and Characterization of Amorphous/Nanocrystalline Al87.5Ni4Sm8.5 Particles Reinforced Crystalline Al Matrix Composites

Metal matrix composites, in which crystalline Al was reinforced by particulates of the Al87.5Ni4Sm8.5 amorphous alloy, were produced using cold pressing and hot extrusion processing. Controlled nanoprecipitation was used to improve the mechanical properties of the amorphous alloy. Amorphous melt-spun ribbons were produced by melt-spinning technique and then fragmented in fine powder by high-energy ball milling. Amorphous and pure aluminum powders were mixed in two different proportions: 85:15 and 70:30 (wt%) and homogenized by ball milling. Bulk samples were produced via cold pressing and hot extrusion. Controlled nanoprecipitation within the amorphous alloy was obtained by the correct choice of processing temperature. The composites were analyzed for reinforcement distribution, porosity content, microhardness and compression tests. The results showed that it was possible to control the precipitation by producing almost the same volume fraction of nanocrystals in each condition. Compression tests showed an improvement on the mechanical properties, which were correlated with the presence of the amorphous/nanocrystals reinforcement in the Al-matrix. The compression yield-strengths of the as-extruded composites were 192 and 310 MPa for 15% and 30% in volume of Al87.5Ni4Sm8.5, respectively. These values are significantly higher than the typically found for the AA1100 wrought pure aluminum (180 MPa).

Consolidation of the Cu46Zr42Al7Y5 amorphous ribbons and powder alloy by hot extrusion

The amorphous Cu46Zr42Al7Y5 alloy presents large supercooled liquid region (ΔTX = 100 K), with a viscosity of about 106 N.s/m2 where the material can flow as a liquid, making it possible an easy deformation in this temperature region. The aim of this work was to analyze processing routes to produce bulks of metallic glasses. Two kinds of materials were used: amorphous powders and ribbons, both were consolidated by hot extrusion in temperatures inside the range between Tg and Tx, with a ram speed of 1 mm/min and extrusion ratio of 3 : 1. Analysis of X-Ray Diffratometry (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM), revealed that the proposed consolidation routes were effective to produce large bulks of amorphous materials, even with the strong decreasing of ΔTX observed after deformation by milling and during extrusion.