Solid state recycling (SSR) is a new approach for making metals recycling more efficient with respect to remelting-based approaches. Friction stir consolidation (FSC) is a new solid-state process ...that is employed to recycle metallic scraps. Until now, a single-step FSC process was applied to recycled metal chips. During the single-step approach, critical processes parameters, especially processing time and rotational speed, are considered vital to control the quality and mechanical properties of the billet. However, the effectiveness of process parameters is highly restricted by challenging masses of recycling chips and machine competency. The present study first highlights the issues of the single-step FSC process, such as unconsolidated billet and poor mechanical properties at the bottom of the part, i.e., far away from the stirring action. Then, for the first time, three different two-step FSC methods were introduced as new approaches to overcome the existing challenges of the single-step method. The effectiveness of these methods was evaluated through the Vickers hardness measurements, and microstructure analysis. The results showed that two-step FSC methods successfully led to a fully consolidated billet and considerably improved mechanical properties.
The optimal conditions of applied factors to reuse Aluminium AA6061 scraps are (450, 500, and 550) ⁰C preheating temperature, (1–15) % Boron Carbide (B4C), and Zirconium (ZrO2) hybrid reinforced ...particles at 120 min forging time via Hot Forging (HF) process. The response surface methodology (RSM) and machine learning (ML) were established for the optimisations and comparisons towards materials strength structure. The Ultimate Tensile Strength (UTS) strength and Microhardness (MH) were significantly increased by increasing the processed temperature and reinforced particles because of the material dispersion strengthening. The high melting point of particles caused impedance movements of aluminium ceramics dislocations which need higher plastic deformation force and hence increased the material's mechanical and physical properties. But, beyond Al/10 % B4C + 10 % ZrO2 the strength and hardness were decreased due to more particle agglomeration distribution. The optimisation tools of both RSM and ML show high agreement between the reported results of applied parameters towards the materials' strength characterisation. The microstructure analysis of Field Emission Scanning Electron Microscopy (FE-SEM) and Atomic Force Microscope (AFM) provides insights mapping behavioural characterisation supports related to strength and hardness properties. The distribution of different volumes of ceramic particle proportion was highlighted. The environmental impacts were also analysed by employing a life cycle assessment (LCA) to identify energy savings because of its fewer processing steps and produce excellent hybrid materials properties.
4Cr5MoSiV (H11) steel machining chips were crushed to a powder and then consolidated into discs by hot pressing under various consolidation parameters. The discs were subjected to modified ...spheroidizing annealing treatment, and their evolved microstructure, tensile mechanical properties and fracture behavior were studied. The microstructure consisted of α−Fe as a matrix, together with heterogeneously distributed non metallic inclusions from the chip-crushing step and precipitated secondary phases. The yield strength, fracture strength and elongation to fracture of the consolidated discs were determined to be in the range of 215∼264 MPa, 344∼415 MPa and 1.2∼2.6%, respectively. The strength of the recycled H11 steel was comparable with that of the ingot metallurgy (IM) H11 steel, but the tensile ductility of the former was significantly lower than that of the latter, being mainly caused by the fracture of the non-metallic inclusions along with the hard secondary phase particles in the IM H11 steel which leads to premature fracture of the samples. The Vickers hardness of the samples were in the range of 144∼194 HV being comparable to that of the IM counterpart. Factographs of the fracture surface demonstrated that the tensile test specimens fractured in a brittle fracture mode.
•The strength of recycled H11 is comparable to that of metallurgy (IM) H11 steel.•The ductility of the recycled H11 is significantly lower than that of the (IM) H11.•Premature fracture is originated by non-metallic inclusions in the IM H11 steel.•The hardness is in the range of 144∼194 HV, comparable to that of IM.
•Environmental assessment of novel technologies to increase material circularity.•Technologies primarily maintain material quality to avoid downcycling.•Technology scenarios have little impact on ...Global Warming Potential.•Recycled content and recycling rate are the key to improved environmental performance.•Energy consumption in beverage can production expected to be the future hotspot.
It is undisputed that the recycling of aluminium is desirable as long as the environmental and economic implications of its reintegration do not exceed the burdens of its primary production. The efficiency of any aluminium recycling system can be expressed by the total material losses throughout the entire process chain, ideally reaching 0%, thus equivalent to 100% metal recovery. However, in most cases metals are recycled in open/cascade recycling loop where dilution and quality losses occur. Innovations in aluminium beverage can (ABC) design as well as in sorting and recycling technologies have the potential to increase recyclability and avoid downcycling issues due to mixed alloy scrap streams. By means of Life Cycle Assessment (LCA) seven scenarios, comprising specific systemic changes, are compared to the current recycling practice of the used beverage can in the UK. The End-of-Life modelling of recycling is performed in accordance with the equal share method to account for impacts both on the recyclability and the recycled content. The results confirm the primary aluminium production and energy consumption in the ABC production as the hotspots in the life cycle of the ABC. The toxicity and energy-related impact categories show the highest susceptibility to increasing recycled content and recycling rate, while the technological novelties show little effect. In terms of abiotic resource depletion the introduction of novel technologies could have the potential to retain quality of the aluminium alloys by either establishing dedicated waste streams or upgrading the aluminium scrap by dedicated sorting strategies.
Solid state recycling refers to a group of processes allowing direct recycling of metals scraps into semi-finished product. Their main advantage lies in avoiding the molten state of the material ...which badly affects the environmental performance of the conventional (remelting based) recycling routes. It is expected that such process category would lower the environmental performance of metals recycling. In this paper, the friction stir extrusion process for aluminum alloy AA 2050 wire production is analyzed under the primary energy demand perspective. The process electrical energy demand is quantified with varying process parameters. An empirical modelling approach was applied and an analytical model able to expresses the specific energy consumption as a function of the extrusion rate was carried out. Finally, the primary energy demand of the whole recycling route was quantified and compared with both conventional and Equal Channel Angular Pressing (ECAP) based routes. Results revealed that Friction Stir Extrusion approach allows substantial primary energy savings for the case of wire production. To be more specific, FSE allows a reduction in energy demand up to 74% and 63% with respect the conventional and the ECAP routes, respectively. This is mainly due to avoided permanent material losses as well as to the absence of intermediated process steps (wire drawing).
•The consolidation recycled Mg-Gd-Y-Zn-Zr billets were recycled from the metal chips through spark plasma sintering process.•The consolidated recycled billets demonstrated the rival compression ...properties compared with the initial billets.•The bond interface between metal chips in the recycled billets presented superior bonding properties and deformation consistency performance with α-Mg matrix.
The consolidation Mg–Gd–Y–Zn–Zr billets containing long period-stacking ordered (LPSO) phase were recycled from the metal chips through the spark plasma sintering (SPS) process, which achieves the effective metallurgical bonding between metal chips. The effects of the sintering parameters on the microstructure characteristic and mechanical properties of the recycled billets were studied. The metal chips were effectively bonded in the recycled billets sintered at 500 °C, however, the metal chips partly melted into semi-solid state as sintering temperature increased to 550 °C. The oxidation films of rare earth (RE) element formed at the bond interface between metal chips during SPS recycling process. The consolidation recycled billets through SPS demonstrated the rival compression failure strain and superior compression stress compared with the referenced cast alloy. The lamellar 14H-LPSO phases hardly precipitate in the vicinity of the bond interface between metal chips after heat treatment with air cooling. However, the furnace cooling facilitates the precipitation of 14H-LPSO phases within the α-Mg grains, even the α-Mg matrix adjacent to the bond interface. The oxide films at the bond interface between the metal chips were zigzagged and fragmented during the isothermal compression. The cracks or holes were hardly observed adjacent to the bond interface during isothermal compression, which reveals superior bond properties and deformation consistency performance between metal chips.
Significant amount of Ti-5553 alloy (a near-beta titanium alloy) swarf is produced during the daily operation of manufacturing high strength titanium alloy components used in industry. However, the ...direct use of the produced swarf is seldom investigated and reported. In this paper, hot pressing was used to recycle Ti-5553 machining swarf to turn the waste into useful material. The hot-pressed Ti-5553 alloy has an ultimate tensile strength (UTS) of 675 ± 12 MPa, strain to fracture of 0.98 ± 0.04%, and bending strength of 1181±28 MPa. After double-aging at 600 ºC for 4 h followed by 700 ºC for 0.5 h, both strength and ductility of hot-pressed Ti-5553 alloy have a significantly improved, with a yield strength (YS) of 1390 ± 20 MPa, UTS of 1425 ± 12 MPa, a strain to fracture of 2.47 ± 0.07%, and a bending strength 2565±35 MPa. These results demonstrate the hot pressing is a viable processing route to recycle Ti-5553 swarf to cost-effectively produce a qualified solid material for post-processing and engineering applications.
Ultrafine grained (UFG) and coarse grained (CG) Al-7Si-0.3Mg (wt%) alloy rods were fabricated by hot extrusion of compacts of a nanocrystalline Al-7Si-0.3Mg alloy powder and coarse grained ...Al-7Si-0.3Mg alloy granules respectively. Both the nanocrystalline powder and the granules were prepared by processing Al-7Si-0.3Mg alloy (widely known as A356 cast alloy) machining chips produced in machining cast components of this alloy such as car wheels. Samples from the rods were also T6 heat treated with a condition of 535 °C/1 h-water quenching-165 °C/8 h. The as-extruded UFG rod exhibited a yield strength (YS) of 298 MPa, ultimate tensile strength (UTS) of 345 MPa and elongation to fracture (δf) of 5.9%, which changed to 223 MPa, 342 MPa and 10.2% respectively after the T6 heat treatment. In contrast, the as-extruded CG rod exhibited a YS of 101 MPa, UTS of 187 MPa and δf of 16.6%, which changed to 203 MPa, 275 MPa and 10.8% after the heat treatment. The UFG Al-7Si-0.3Mg alloy sample exhibits a dramatically different precipitation behavior from the CG Al-7Si-0.3Mg alloy sample during the T6 heat treatment, with the formation of fine platelet-shaped pre-β″ precipitates on Al {001} planes in the former sample in contrast of the formation of needle-shaped β″ precipitates along Al directions in the latter sample. The change of precipitation behavior leads to a weaker precipitation hardening effect. This work demonstrated that a significantly higher tensile strength can be achieved with heat treated UFG Al-7Si-0.3Mg alloy than CG Al-7Si-0.3Mg without sacrificing tensile ductility.
•Time- and cost-efficient estimation of fatigue strength of aluminum profiles.•Application of continuous cyclic load increase procedure.•Qualification of solid-state recycled aluminum chip ...profiles.•Mechanism-related differences in cyclic deformation and creep behavior.•Fractographic correlation of results of load increase tests and creep behavior.
Because of the great potential to reduce the amount of energy, the direct recycling of scrap like aluminum chips by hot extrusion is a hopeful alternative to the usual remelting process. Previous investigations showed that the chips, which are encased by oxide layers, are elongated due to the extrusion process. Therefore, the aim of this study is to test to what extend anisotropic properties, in analogy to fiber-reinforced materials, can be determined. The mechanical properties of cast-based and chip-based specimens with orientations of 0°, 30° and 90° to extrusion direction were characterized by means of mechanical quasistatic and cyclic experiments. It could be shown that quasistatic properties of the 0° orientation are highest for chip-based specimens, whereby the differences to the other orientations are slight. On the other hand, large differences in cyclic creep behavior between the orientations as well as in damage behavior could be determined.
In this study, the possibility of solid-state recycling of aluminium alloy machining swarf using cold extrusion and a subsequent cold rolling process is investigated. Cast Al–Si alloy swarf was cold ...compacted into billets and successfully profile-extruded into square bars with a rectangular cross-sectional aspect ratio of 1:1.8 under an extrusion ratio of 4 or more. After annealing, the extruded bars underwent multi-pass cold rolling into 1-mm thick strips with a total rolling reduction of 85%. Optical microscopy demonstrated that in material recycled using only an extrusion process, coarse residual voids existed in regions where insufficient plastic strain was introduced, causing a visible expansion of the material during heat treatment. However, uniaxial tensile tests showed that extrusion-recycled material had a higher mechanical strength than the original aluminium alloy, implying sufficient bonding among the individual pieces of machining swarf. It was also found that the strength and density of material recycled through extrusion and an additional rolling process were superior to material recycled using extrusion only. Moreover, it was observed that the ductility of the recycled materials was inferior to that of the original aluminium alloy.
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