Solid-state Recycling Research Articles

Feasibility Study of Solid-State Recycling through Direct Hot Rolling of AA5754 Aluminum Chips for Automotive Applications

Recently, researchers have done a lot of efforts to develop new solid-state recycling processes, both experimentally and developing numerical models. This kind of process is energy-saving and environmentally friendly compared to the conventional aluminum recycling process because avoided the melting step. The purpose of this work is to evaluate the feasibility of an innovative solid-state recycling process through direct hot rolling in a non heat-treatable aluminum alloy for automotive applications. AA5754 chips have been produced by turning a bar without the usage of lubricants and compacted with a 150 kN load; the compacted billets were treated at 400 °C and directly hot rolled in several successive passes. Rolled samples are then analyzed in terms of Vickers microhardness and microstructure in both as-rolled and heat treatment conditions, this last was performed at 185°C simulating the process of paint-bake. The produced samples show an excellent bonding between chips.

Study on hot deformation behavior and dynamic recrystallization mechanism of recycled Al–Zn–Mg–Cu alloy

This study utilized Al–Zn–Mg–Cu alloy chips as raw materials to prepare recycled billets through a solid-state recycling process. Isothermal hot compression tests were conducted using a thermal simulation machine to establish an Arrhenius-type constitutive equation and the hot processing map based on the dynamic materials model. The microstructure of the recycled Al–Zn–Mg–Cu alloy after hot compression was characterized and analyzed using SEM, EBSD, and TEM, exploring the microstructural evolution mechanisms of the recycled alloy at different temperatures and strain rates. The results indicate that the optimal hot deformation parameters for the recycled Al–Zn–Mg–Cu alloy are 300–360 °C at a strain rate of 0.01–0.05 s⁻1 and 400–450 °C at a strain rate of 0.05–0.3 s⁻1. At the same strain rate, as the deformation temperature increases, low-angle grain boundaries gradually disappear, and the grain structure becomes more stable. Dynamic recrystallization replaces dynamic recovery as the dominant mechanism. At the same deformation temperature, low strain rates allow more time for the migration of low-angle grain boundaries, thereby promoting the growth of dynamically recrystallized grains and ultimately forming new, undistorted grains.

Tensile and shear behavior of recycled AA 6060 aluminium chips by direct hot extrusion

Solid state recycling of aluminium chips is a promising technique to reduce environmental impacts of secondary production. As the recycling process induces a highly oriented microstructure, this study aims to quantify the mechanical properties of extrudates and identify the role of chip boundaries in the fracture behavior. Tensile and shear tests are performed on heat treated AA 6060 alloy and analyzed using digital image correlation. The tensile behavior of the chip-based material is similar to its cast-based counterpart, reaching a yield strength of 230 MPa. Shear properties are close for small deformations, although the chip-based material have lower ductility due to the early onset of damage at the chip boundary. These results confirm the industrial relevance of this process for large scale recycling of aluminium.

Effect of process parameters on the mechanical properties of wires produced from A356 aluminum alloy chips by Continuous Friction Stir Extrusion: Experiments and numerical simulation

Recycling of metals is becoming crucial from an economic and environmental point of view. The solid-state recycling process Continuous Friction Stir Extrusion was used to produce wires out of A356-T6 chips. The mechanical properties of the produced wires were explored by varying the main process parameters. Characterization involved Vickers hardness tests, tensile tests, grain size measurements, and fracture surface analysis. It has been found that it is possible to achieve 77 % of the Ultimate Tensile Strength (UTS) and 92 % of Vickers hardness with respect to the as-fabricated A356 alloy. The average grain size increases with the tool rotational with values ranging from about 9 µm to about 11 µm. A 3D dedicated numerical model was used to predict the distributions and histories of primary field variables, and to calculate the Piwnik-Plata parameter, fostering a more in-depth understanding of the process mechanics. This allows for the precise prediction of unacceptable product quality of the bonding when the Plata and Piwnik parameters are low. Predicted temperature close to the rotating tool should reach 400 °C while the cochlea temperature should be below 100 °C for sound wires production thus avoiding early chip bonding and process failure.

Solid-state recycling of magnesium and its alloys via plastic deformation: An overview of processing and properties

The increasing demand for primary magnesium production poses significant environmental challenges, aggravated by the limited availability of raw materials, which can hinder supply. Consequently, the recycling of magnesium chips and waste is gaining importance. While conventional remelting techniques are prevalent as they suffer from drawbacks including high energy consumption, material loss, low purity, and inferior mechanical properties. Solid-state recycling (SSR) via plastic deformation processes has been introduced as a promising alternative for producing ultrafine-grained (UFG) magnesium materials with outstanding properties. Despite the absence of any reviews on SSR using plastic deformation methods for magnesium, this paper offers a detailed examination of SSR techniques. The mechanisms of bonding and grain refinement, crucial for determining the final properties of recycled magnesium, are explored. Furthermore, the discussion delves into corrosion, an essential aspect concerning magnesium and its alloys. Ultimately, the impact of various parameters such as process temperature, level of shear strain, chips size, and hydrostatic pressure on the quality of the final sample, to be used as guidance for the production of better-qualified specimens was examined.

Mechanical behavior of hot extruded aluminum 6082 chip.

In a bid to address the energy-intensive nature of primary aluminum production, this study explores the solid-state recycling of aluminum alloy 6082 chips through direct hot extrusion. Compacted at room temperature, chips were extruded at temperatures (350, 425, and 500°C) and reduction ratios (6, 8.5, and 11) to optimize mechanical properties. Extensive analyses, including ANOVA and linear regressions, of strength, density, and microstructure revealed significant influences of those extrusion parameters. Optimizing these parameters within the study's aforementioned working ranges can impact the recycled material's strength; with a 36% reduction ratio increase and 20% temperature increase modestly reducing ultimate strength (2%), while a 20% temperature increase alone lowers yield strength more noticeably (9%). These findings highlight the potential for enhanced recycling and sustainable manufacturing.

Tensile Strength Enhancement Via Heat Treatment In Directly Recycled Aluminium Alloy (AA6065)

Products made through solid-state recycling of aluminum chips in a hot extrusion process were regulated by temperature-related factors by utilizing a preheating temperature of 350 °C, 400 °C, and 450 °C for one hour, two hours, and three hours of preheating time, respectively. Design of Experiments (DOE) was used, and the findings showed that the preheating temperature is more significant to manage than the preheating duration, and that increasing the temperature led to a high tensile strength. This conclusion was reached as a result of the experiments. The profile that was extruded for three hours at 550 degrees Celsius had reached the ideal condition for achieving the highest possible tensile strength. The heat treatment was carried out with the solution temperature set at 450 degrees Celsius for two hours, and the ageing procedure was carried out at 195 degrees Celsius for three hours. The extruded specimen underwent heat treatment, which resulted in a considerable increase in its tensile strength.

Effect of compaction pressure on cold compaction of AA2024 swarf generated during milling operation

The solid-state recycling of aluminium swarf is a promising alternative to the conventional practice of remelting, which can lead to the loss of aluminium. The compaction process is an important step in the solid-state recycling of aluminium swarf. This study investigated the effect of cold compaction pressure on the material behaviour, density, and microstructure of compacted AA2024 machining swarf. The milling swarf was initially cleaned and chemical composition analysis was carried out. Morphology of swarf particle exhibited a wavy and straight regions attributable to milling conditions. The swarf then compacted at room temperature for 3 different pressure level viz. 1000, 1500, and 2000 kgf/cm2. The results showed that the density of the compacts increased with the increase in compaction pressure, reaching a value of 85% of the density of AA2024 at a pressure of 2000 kgf/cm2. Microstructure was analysed using scanning electron microscope to understand the bonding at the the swarf-swarf particle boundary. Vickers hardness results indicated that the hardness values of the compacted specimens also increased slightly with increasing compaction pressure. The overall combination of factors viz. plastic deformation, reorientation, rupturing of oxide layers, and mechanical interlocking contributes to the strength and compaction of swarf particles when subjected to higher compaction pressure used in this study. Further studies are in progress to improve the densification of the compacted specimens and to evaluate their suitability for extrusion applications.

Solid state recycling of aluminium chips: Multi-technique characterization and analysis of oxidation

Solid-state recycling of metallic alloys is a promising alternative method which avoids remelting and reduces significantly the CO2-emission compared to remelting. Contamination being critical for solid-state recycling, the objective of this study is to quantify and localize oxygen contamination at each step of the process. Pre-compacted AA6060 aluminium alloy machining chips were hot-extruded. The oxygen intake and the formation of oxides were quantified and localized through a multi-technique characterization, including X-ray photoelectron spectroscopy and transmission electron microscopy. The overall oxygen content is found to increase at every step of the recycling process. Analyses reveal that the initial thin Al2O3 layer on the chips gets covered by a MgO layer during pre-annealing and hot extrusion. Thus, alloying elements, as Mg, are involved in oxidation. It results in a tenfold increase of the oxygen content in the extrudate accompanied by a complex network of oxides with an average thickness of 290 nm and a low density. Thus, tuning processing parameters is a promising leverage to limit oxidation and improve chip welding, which will probably depend on the alloying elements.

Sustainability Study of a New Solid-State Aluminum Chips Recycling Process: A Life Cycle Assessment Approach

Nowadays, reducing greenhouse gas emissions in all human activities has become crucial. This article presents a life cycle assessment (LCA) investigation conducted to evaluate the environmental benefits of a newly developed solid-state recycling process for aluminum chips, involving two steps: direct rolling and accumulative roll bonding. A comparison was made between this process and two current industrial methods of recycling aluminum scraps to obtain wrought products, which involve melting, casting, and subsequent rolling. The LCA analysis considered a scenario where 50% of the total electric requirement was met by photovoltaic energy. The results of the study indicate that in all examined impact categories, direct rolling has a lower environmental footprint compared to both traditional recycling and twin-roll cast technology. These results suggest that this new solid-state recycling procedure has significant potential to replace environmentally harmful melting processes.

Numerical Modeling of a Sustainable Solid-State Recycling of Aluminum Scraps by Means of Friction Stir Extrusion Process.

One of the most important purposes of the modern industry is a sustainable production, considering the minimization of the energy and of the raw materials used, together with the reduction of polluting emissions. In this context, Friction Stir Extrusion stands out, since it allows to obtain extrusions starting from metal scraps deriving from traditional mechanical machining processes (e.g., chips deriving from cutting operations), heated only by the friction generated between the scraps and the tool, so avoiding the material melting phase. Given the complexity of this new kind of process, the objective of this research is the study of the bonding conditions considering both the heat and the stresses generated during the process under different working parameters, namely tool rotational and descent speeds. As a result, the combined approach involving the Finite Element Analysis and the Piwnik and Plata criterion proves to be a valid tool for forecasting if bonding phenomenon occurs and how it is influenced by the process parameters. The results have also demonstrated that it is possible to achieve completely massive pieces between 500 rpm and 1200 rpm, but at different tool descent speeds. Specifically, up to 1.2 mm/s for 500 rpm and just over 2 mm/s for 1200 rpm.

Comparison between spark plasma sintering and hot extrusion for solid-state recycling of Al-Si-Cu-Fe alloy chips

Comparison between spark plasma sintering and hot extrusion for solid-state recycling of Al-Si-Cu-Fe alloy chips

Green recycling of short-circuited garnet-type electrolyte for high-performance solid-state lithium batteries

Solid-state lithium batteries (SSLBs) solve safety issues and are potentially energy-dense alternatives to next-generation energy storage systems. Battery green recycling routes are responsible for the widespread use of SSLBs due to minimizing environmental contamination, reducing production costs, and providing a sustainable solution for resources, e.g., saving rare earth elements (La, Ta, etc.). Herein, a solid-state recycling strategy is proposed to achieve green recycling of the crucial component solid-state electrolytes (SSEs) in spent SSLBs. The short-circuited garnet Li6.5La3Zr1.5Ta0.5O12 (LLZTO) is broken into fine particles and mixed with fresh particles to improve sintering activity and achieve high packing density. The continuous Li absorption process promotes sufficient grain fusion and guarantees the transformation from tetragonal phase to pure cubic phase for high-performance recycled LLZTO. The Li-ion conductivity reaches 5.80 × 10-4 S cm−1 with a relative density of 95.9%. Symmetric Li cell with as-recycled LLZTO shows long-term cycling stability for 700 h at 0.3 mA cm−2 without any voltage hysteresis. Full cell exhibits an excellent cycling performance with a discharge capacity of 141.5 mA h g−1 and a capacity retention of 92.1% after 400 cycles (0.2C). This work develops an environmentally friendly and economically controllable strategy to recycle SSE from spent SSLBs, guiding future directions of SSLBs large-scale industrial application and green recycling study.

The Effect of Process Control Agent and Milling Time on the Solid-State Recycling by Mechanical Milling of Ti-6al-4v Alloy Scraps

The Effect of Process Control Agent and Milling Time on the Solid-State Recycling by Mechanical Milling of Ti-6al-4v Alloy Scraps

Solid State Recycling of Vanadis®8 Steel Scraps Using Powder Metallurgy

Solid State Recycling of Vanadis®8 Steel Scraps Using Powder Metallurgy

Solid state recycling of used aluminum alloy beverage cans by thermomechanical consolidation

ABSTRACT Solid-state recycling of used aluminum alloy beverage cans was accomplished by thermomechanical consolidation of the sheet fragments produced by shredding the cans. Different samples were obtained using two thermomechanical consolidation routes, one involving direct hot extrusion of a sheet fragment compact and the other involving upset hot-forging of a sheet fragment compact followed by hot extrusion of the forged ingot. The microstructures and mechanical properties of the samples were investigated. It was found that the samples contained less pores and exhibited better mechanical properties with a higher extrusion temperature and involving upset forging than with only hot extrusion, the highest tensile strength is 209.5 MPa and the largest elongation to fracture is 29.1%. The surface layers of the samples exhibited a clearly higher strength and tensile ductility than the interior. They also showed significantly different fracture behaviors, with the former being like fully ductile fracture and the latter involving delamination of the sheet fragments, suggesting that the bonding between the fragments is significantly stronger in the surface layer, possibly due to a higher amount of plastic deformation in it. Overall, the best quality solid state recycled material has tensile properties comparable with those of wrought aluminum alloy with the same composition.

Forgeability characterization of multi-material based functionally graded materials manufactured through friction stir consolidation

Solid state recycling allows direct recycling of metal chips into semi-finished products. This process category proved to lower the environmental impact of metals recycling. Friction stir consolidation (FSC) is a new solid-state technique taking advantage of friction heat generation and severe plastic deformation to consolidate chips into billets. The new frontier of FSC process could be its evolution from recycling techniques towards the concept of upcycling technique: reuse (discarded objects or material) in such a way as to create a product of higher quality or value than the original. The authors have recently successfully applied FSC for producing multi-material based functionally graded materials (FGM). In this paper, the forgeability of the billet consolidated out of two dissimilar aluminium alloys AA 7075 and AA 2011-T3 chips, was analyzed. A proper forging test was designed, and mechanical and metallurgical properties of the forged parts were assessed through Vickers hardness measurements.

Solid state recycling of Mg–Gd–Y–Zn–Zr alloy chips by isothermal sintering and equal channel angular pressing

The Mg-7Gd-4Y-2Zn-0.5Zr alloy chips were successfully recycled through isothermal sintering and equal channel angular pressing (ECAP). The mechanical properties and microstructure evolution of samples during the recycling process were studied in detail. The eutectic phases in the as-cast alloy transform into long period-stacking ordered (LPSO) phases after homogenization, which can improve the plasticity of the material. After isothermal sintering, the density of the sample is lower than that of the homogenized sample, and oxide films are formed adjacent to the bonding interface of the metal chips. Hence, the plasticity of the sintered sample is poor. Dense samples are fabricated after ECAP. Although the grains are not refined compared to the sintered sample, the microstructure becomes more uniform due to recrystallization. Fiber interdendritic LPSO phase and kinked 14H-LPSO phase are formed in the alloy due to the shear deformation during the ECAP process, which improves the strength and plasticity of the sample significantly. Furthermore, the basal texture is weakened due to the Bc route of the ECAP process, which can increase the Schmid factor of the basal slip system and improve the elongation of the sample. After 2 ECAP passes, the fully densified recycled billet shows superior mechanical properties with an ultimate tensile strength of 307.1 MPa and elongation of 11.1%.

Fabrication of Billet from Aluminum Alloys AA 2011-T3/7075 Chips through Friction Stir Consolidation

Recently evolving Solid-State Recycling (SSR) techniques have shown promising features to recycle metals scraps more efficiently compared to remelting-based approaches. Among these SSR methods, Friction Stir Consolidation (FSC) has been successfully tested to transform metals chips directly into semi or final solid products. Therefore, researchers explored FSC critical process parameters and their subsequent effects on quality in terms of the mechanical and metallurgical properties of the billet. All the previous studies of FSC were limited to developing billet of mono materials. Therefore, in this research, an attempt was made to go beyond the idea of recycling; in fact, a billet of two dissimilar aluminum alloys AA 7075 and AA 2011-T3 out of chips was obtained. The mechanical and metallurgical properties were assessed through the Vickers hardness measurements and microstructure analysis. The experimental results of this research illustrate that the FSC process is a feasible approach to develop a billet of dissimilar materials with achieving quality closer to the corresponding billet of mono-material.

Correction to: Analysis of Densification and Consolidation during the Solid-State Recycling of High Purity Titanium Chips

Correction to: Analysis of Densification and Consolidation during the Solid-State Recycling of High Purity Titanium Chips