Compaction of aluminium foil and its effect on oxidation and recycling yield

This is a post-peer-review, pre-copyedit version of an article published in Light Metals 2021, Part of the The Minerals, Metals & Materials Series book series (MMMS). The final authenticated version is available online at: https://doi.org/10.1007/978-3-030-65396-5_96One of the problems when recycling aluminium is its oxidation and consequent metal loss. This is especially critical for the thin sheet/foil materials used for food packaging applications. Compacting the scrap into briquettes may partly reduce such losses in addition to facilitate transport and storage. Shredded aluminium materials of different thicknesses (15-300 microns) were compacted into cylindrical briquettes of 4 cm diameter, each weighting 20 g by uniaxial pressure or moderate-pressuretorsion. A sub-set of briquettes and chips was subsequently oxidized at 650 C, while a sub-set was left untreated. Finally, all samples were re-melted under molten protective salt-flux. Compacting reduced the specific oxidation during the heat-treatment and promoted the coalescence and yield for the heat-treated materials. Both effects were most significant for the thinnest foil in the study (15 microns). The material thickness influenced the porosity and surface roughness of the resultant briquette, as well as the pressure required to reach a given bulk density.acceptedVersio

Depth profiling at a steel-aluminum interface using slow-flow direct current glow discharge mass spectrometry

Direct current glow discharge mass spectrometry (dc-GDMS), which relies on sector field mass analyzers, is not commonly used for depth profiling applications because of its slow data acquisition. Nevertheless, dc-GDMS has good reproducibility and low limits of detection, which are analytical features that are encouraging for investigating the potential of dc-GDMS for depth profiling applications. In this work, the diffusion of traces of chromium and nickel was profiled at the interface of a steel-aluminum bilayer using a new sensitive dc-GDMS instrument. The depth profile of the non-treated sample was compared with that of a heat-treated specimen at 400°C for 30 min. Scanning electron micrographs, energy dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA) were used to study the diffusion process. The results of the study show that both chromium and nickel are enriched at the steel-aluminum interface, with higher concentrations of both elements for the heat-treated specimen. Two peaks for both chromium and nickel were clearly present at the interface, with a high concentration of chromium in the aluminum layer. This observation is likely a consequence of elemental diffusion from the interface towards the aluminum layer. The presence of the third layer, steel beneath the aluminum layer, might also have contributed to this observation.acceptedVersio

Hydrides of Laves type Ti–Zr alloys with enhanced H storage capacity as advanced metal hydride battery anodes

The present work was focused on the studies of the effect of variation of stoichiometric composition of Ti–Zr based AB2±x Laves phase alloys by changing the ratio between A (Ti + Zr) and B (Mn + V + Fe + Ni) components belonging to both hypo-stoichiometric (AB1.90, AB1.95) and over-stoichiometric (AB2.08) alloys further to the stoichiometric AB2.0 composition to optimize their hydrogen storage behaviours and performances as the alloy anodes of nickel metal hydride batteries. AB2-xLa0.03 Laves type alloys (A = Ti0.15Zr0.85; B = Mn0.64–0.69V0.11–0.119Fe0.11–0.119Ni1.097–1.184; x = 0, 0.05 and 0.1) were arc melted and then homogenized by annealing. The studies involved probing of the phase-structural composition by X-Ray diffraction (XRD), together with studies of the microstructural state, hydrogen absorption–desorption and thermodynamic characteristics of gas–solid reactions and electrochemical charge-discharge performance, further to the impedance spectroscopy characterization. The alloys were probed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and XRD. These studies concluded that the alloys contained the main C15 FCC Laves type AB2 intermetallic co-existing with a secondary C14 hexagonal Laves phase and a small amount of LaNi intermetallic

Recycling of automotive aluminum

With the global warming of concern, the secondary aluminum stream is becoming an even more important component of aluminum production and is attractive because of its economic and environmental benefits. In this work, recycling of automotive aluminum is reviewed to highlight environmental benefits of aluminum recycling, use of aluminum alloys in automotive applications, automotive recycling process, and new technologies in aluminum scrap process. Literature survey shows that newly developed techniques such as laser induced breakdown spectroscopy (LIBS) and solid state recycling provide promising alternatives in aluminum scrap process. Compared with conventional remelting and subsequent refinement, solid state recycling utilizing compression and extrusion at room or moderate temperature can result in significant energy savings and higher metal yield

Application of EBSD technique to ultrafine grained and nanostructured materials processed by severe plastic deformation: Sample preparation, parameters optimization and analysis

With the help of FESEM, high resolution electron backscatter diffraction can investigate the grains/subgrains as small as a few tens of nanometers with a good angular resolution (∼0.5°). Fast development of EBSD speed (up to 1100 patterns per second) contributes that the number of published articles related to EBSD has been increasing sharply year by year. This paper reviews the sample preparation, parameters optimization and analysis of EBSD technique, emphasizing on the investigation of ultrafine grained and nanostructured materials processed by severe plastic deformation (SPD). Detailed and practical parameters of the electropolishing, silica polishing and ion milling have been summarized. It is shown that ion milling is a real universal and promising polishing method for EBSD preparation of almost all materials. There exists a maximum value of indexed points as a function of step size. The optimum step size depends on the magnification and the board resolution/electronic step size. Grains/subgrains and texture, and grain boundary structure are readily obtained by EBSD. Strain and stored energy may be analyzed by EBSD

Effects of cryogenic temperature and pre-stretching on mechanical properties and deformation characteristics of a peak-aged AA6082 extrusion

Plastic deformation studies of a peak-aged AA6082 alloy by means of tensile tests at 77 K and 295 K, and related microstructure characteristics obtained by Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), Transmission Electron Microscopy (TEM) and Atom Force Microscopy (AFM), revealed new results. A simultaneous improvement in ductility and strength occurred at 77 K, but not at 295 K. A higher work hardening accompanied by a more homogeneous slip mode explained the improved properties at 77 K. Pre-stretching at these two temperatures and subsequent tensile testing at room temperature revealed a marked yield point. However, pre-stretching at 77 K exhibited a slightly higher room temperature yield strength and ductility than the condition pre-stretched at 295 K. Annealing after pre-stretching improved ductility and reduced the magnitude of the yield point. Pre-stretching at 77 K and subsequent annealing introduced somewhat higher strength and ductility as compared to the counterpart pre-stretched at 295 K. The observed mechanical behaviour and associated phenomena were directly linked to microstructure characteristics such as deformation substructure history, slip localization, dislocation density and the precipitate β' /β'' ratio

Comparative study of eutectic Al-Si alloys manufactured by WAAM and casting

Wire and arc additive manufacturing (WAAM) of metallic materials is expected to become part of the new industrial revolution. The possibilities for complex designs and superior mechanical properties can in many cases replace traditional manufacturing processes such as casting. In order to benchmark the properties of aluminium WAAM components, a comparative study was performed with two different casting techniques: permanent casting with steel mould and sand mould casting. Aluminium-silicon alloys with near eutectic composition were used for the comparison. Porosity levels, secondary dendrite arm spacing, grain size distribution, tensile strength and microhardness were considered for the comparison. The WAAM material exhibited superior mechanical properties originating from a finer dendritic and eutectic microstructure compared with the castings. A slight anisotropy in tensile ductility was observed in the WAAM material, probably due to a coarse microstructural zone between individual beads. All investigated materials had low levels of porosity, < 1% by area fraction. The comparative study has shown that WAAM of aluminium-silicon alloys is well suited for high-integrity applications.publishedVersio

Wire and Arc Additive Manufacturing with TiC-Nanoparticle Reinforced AA5183 Alloy

Wire and arc additive manufacturing of aluminium-ceramic composites shows great potential to produce high strength materials. By incorporation of nanoparticles in the feedstock wire, fine-grained material with low susceptibility for solidification cracking and enhanced strength can be obtained. In fact, this study utilised the novel screw extrusion method to prepare an aluminium alloy containing TiC nanoparticles. The commercial aluminium alloy AA5183 was selected for WAAM to assess and benchmark the effects of screw extrusion and TiC. The materials have been assessed in terms of microstructure, porosity content and mechanical properties. The presence of TiC reduced the average grain diameter by 70%, while Vickers hardness increased with 13%. However, number of pores per unit volume increased by one order of magnitude. The porosity is believed to stem from hydrogen introduced in the AA5183-material through screw extrusion processing, in addition to hydrogen trapping and pore nucleation on TiC nanoparticles.publishedVersio

Optimization of EBSD parameters for ultra-fast characterization

Ultra-fast pattern acquisition of electron backscatter diffraction and offline indexing could become a dominant technique over online electron backscatter diffraction to investigate the microstructures of a wide range of materials, especially for in situ experiments or very large scans. However, less attention has been paid to optimize the parameters related to ultra-fast electron backscatter diffraction. The present results show that contamination on a clean and unmounted specimen is not a problem even at step sizes as small as 1 nm at a vacuum degree of 6.1 × 10−5 Pa. There exists an optimum step size at about 50 data acquisition board units. A new and easy method to calculate the effective spatial resolution is proposed. Effective spatial resolution tends to increase slightly as the probe current increases from 10 to 100 nA. The fraction of indexed points decreases slightly as the frame rate increases from 128 patterns per second (pps) to 835 pps by compensating the probe current at the same ratio. The value 96 × 96 is found to be the optimum pattern resolution to obtain optimum speed and image quality. For a fixed position of electron backscatter diffraction detector, the fraction of indexed points as a function of working distance has a maximum value and drops sharply by shortening the working distance and it decreases slowly with increasing the working distance

Effect of cryorolling on microstructure and mechanical properties of a peak-aged AA6082 extrusion

Peak-aged AA6082 flat extrusions were cryorolled at liquid nitrogen temperature to three different thickness reductions, the reductions were 21%, 42% and 85%, respectively. Microstructure and plastic deformation behaviors of the initial as well as the rolled materials were studied by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests at room temperature. The initial material showed fibrous grain structure. After cryorolling to 21% thickness reduction, grains in the alloy were obviously elongated and importantly, microband traces were detected in selected grains. More detailed information was obtained in the alloy after 42% thickness reduction. Here, numerous microbands aligned along slip planes with the highest resolved shear stress, producing fragmentation of grains, while rests of elongated grains were microband-free. A cryorolling strain of 85% has been found to be desirable for producing a hierarchical microstructure in the materials volume, featuring nano- and ultrafine grains with size <100 nm coexisted with micro-sized grains. The development of hierarchical microstructure could be considered as a consequence of the intersection between families of microbands. As a result, both the strength and uniform elongation of the severely cryorolled alloy, i.e. 85% thickness reduction, were more superior to other rolled alloys. Therefore, this study revealed that the single processing procedure, i.e., cryorolling, can be utilized to tailor for desired properties in favor of both strength and ductility for peak-aged AA6082 extrusions