The energy demand and CO2 emissions of the steel processing industry are a global challenge. During conventional steel processing, the treatment of iron ore and steel in a molten state heavily ...contributes to this problem. This paper provides an in-depth investigation of the benefits and technical requirements of an alternative processing pathway with minimal energy and CO2 burdens. Our proposed method, scrap metal consolidation (SMC) by rolling, is adapted from roll bonding, a scalable metal bonding technique, commonly used for niche composite applications to achieve material properties unattainable by monolithic alloy design. SMC transforms steel scrap into hot rolled steel in solid state without melting. Based on pre-published high-fidelity industrial data, we determined that processing hot rolled steel from scrap in the solid state would consume 94% less energy compared to the primary steel processing route with 94% less CO2 burden. Compared to conventional recycling methods, the energy savings of SMC would be 86%, with an 84% decrease in CO2 emissions. The proposed method is described in detail, and the process windows for AISI 1008 mild steel and SS304 stainless steel were determined in terms of rolling temperature and reduction using a lab-scale rolling mill at a temperature range of 700–1100 °C. The formability of the consolidated mild steel is also evaluated via the hemisphere punch test, a standard industrial test for assessing the formability of sheet metals. While the fracture height of consolidated specimens is in the 9.27–10.62 mm range, the monolithic sample has a fracture height of 10.34 mm. The test results show that the consolidated sheets have comparable formability to monolithic specimens. These investigations altogether demonstrate that SMC-by-rolling is a feasible and environmentally sustainable alternative for conventional steelmaking or recycling processes.
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•Solid-state consolidation of steel scrap uses 94% less energy than primary processing.•Compared to recycling, scrap metal consolidation saves 84% of process CO2 emissions.•Process boundaries for mild and stainless steel follow a reverse S-curve trend.•Test results exhibit comparable formability for roll-bonded and monolithic samples.•Most sheet metal forming operations don't cause opening stress, reducing failure risk.
ABSTRACTThe microstructure and mechanical properties of recycled AA6063 aluminum alloy rods fabricated by hot extrusion of forging compacts formed by upsetting compacts of small AA6063 aluminum alloy ...pieces with different Fe contents before and after T6 heat treatment were studied. In the as-extruded state and with the higher extrusion ratio of 25:1, the microstructure consists of fully recrystallized grains, but the high iron content regions exhibit clearly finer equiaxed grains due to the stronger grain boundary pinning and nucleation effects of a higher number density of Fe-rich phase particles. Increasing the extrusion ratio increases both the strength and ductility of the as-extruded material. The reason is that increasing extrusion ratio enhances the bonding strength of the prior boundaries between the strips formed by deformation of the small pieces. In the T6 heat-treated state, increasing the extrusion ratio from 9:1 to 25:1 clearly increases the fraction of fine and equiaxed grains. The enhancement of the bonding strength and the refinement of the microstructure with the increase of extrusion ratio cause the yield strength and ultimate tensile strength to increase from 174 and 221 MPa to 213 and 237 MPa, respectively, and the elongation to fracture to decrease from 22.1 to 15.4%. Solid-state recycled samples all exhibit a ductile fracture behavior despite formation of microcracks at the prior boundaries.
•The solid state recycling methods based on severe plastic deformation are reviewed.•The solid state recycling methods based on powder metallurgy are summarized.•The mechanism of bonding of Al chips ...and relevant theoretical modes are mentioned.•Factors effecting the density and microstructure of recycled product are analyzed.•Future prospects for the solid state recycling of Al chips are presented.
In contrast with the conventional remelting recycling of aluminum and its alloy chips, the solid state recycling techniques, which can convert the chips directly into dense bulk materials, have attracted significant attention primarily because it possesses many advantages including lower energy consumption, lower metal loss as well as almost no emissions of harmful gases and solid wasters. In this keynote paper, with a view to the current researches of the solid state recycling techniques based on the severe plastic deformation (SPD) and powder metallurgy (P/M), the characteristics and applications of several typical methods, such as hot extrusion, equal channel angular pressing (ECAP), cyclic extrusion compression (CEC), friction stir extrusion (FSE), high pressure torsion (HPT), screw extrusion and spark plasma sintering (SPS), are introduced. A growing number of researches and literatures suggest that the mechanical properties of solid state recycled specimens are primarily dependent on the chip bonding quality and microstructure of the corresponding bulk materials. Then, the mechanism analysis of consolidation of chips is carried out, and three relevant theoretical modes, characterizing the bonding quality, are also mentioned. Moreover, the factors influencing the density and microstructure of chip-consolidated product are discussed comprehensively. Eventually, recommendations in the improvement of solid state recycling techniques and the future prospects are put forward.
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.
AbstractIntroduction: : The purpose of this research is solid state recycling of 3000 and 5000 series aluminum alloy scrap to produce aluminum nano-crystalline powder by mechanical milling without ...using process controlling agent. In this regard, aluminum used beverage cans (UBCs) which consist of lid (alloy 5182) and the monolith part (alloy 3004) of the body (thin) and bottom (thicker).Methods: To achieve disintegration mechanism, lid part, body and bottom of monolith part are separated each other because of diverse constituent of Al series and different thickness. The three parts individually were decoated then cut into the small chips (app. 8 mm). The chips were mechanically ball milled at different times up to 104 hours under argon atmosphere. The ratio of ball to powder was 10 to 1. Findings: The lid part chips are crushed faster than the monolith part chips, and, resulting in a finer powder. According to the PSA results, the D90 of the lid powder is less than 150 micrometers; while D90 of the body and bottom powders are more than 150 micrometers. This result can be used on an industrial scale to separate the constituent elements of crushed UBCs from each other. The smallest D90 values of lid, body and bottom powders, which obtained after 72, 80 and 80 h as optimum milling time, are 109, 258 and 391, respectively. Also, their flowability were 57.8, 59.3 and 61.1 s/50 g, as well as the apparent density were 1.38, 1.43 and 1.46 g/cm3, respectively.
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.
This work investigates the applicability of spark plasma sintering (SPS) as a solid state recycling technique for magnesium alloy scrap. In this respect, machining chips from pure Mg and AZ31 Mg ...alloy ingots are chemically cleaned, cold compacted and SPSed directly into bulk specimens. It is found that SPS can successfully establish full densification and effective metallurgical bonding between chips without altering compositional constituents. This is attributed to the dynamic compaction during sintering as well as to the disruption of the chips' surface oxide film due to SPS electric current based joule heating. Apart from the successful consolidation, microstructural analysis of the initial Mg ingots, chips and SPS recycled material reveals that the SPS microstructure was finer than that of the original ingots due to significant deformation induced grain refinement during machining. As a result, the recycled materials had a higher compression and shear strength than that of the starting ingot material. The findings indicate that SPS is an effective alternative method for solid state recycling of magnesium alloy scrap.
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•Spark plasma sintering is found to be a successful solid state recycling technique for the consolidation of Mg alloy chips.•Fast and full densification/consolidation of Mg alloy machining chips directly into bulk semi-finished products was acheived.•The total recycling route resulted in a finer microstructure than that of the parent material.•The strong bonding and the finer microstructure of the recycled samples improved the mechanical properties.
The possibility to directly extrude semi-finished products using a solid-state-recycling process is a promising alternative to the remelting process, which is highly energy-intensive. Therefore, ...aluminium chips, normally considered as scrap, are used as the basis for the recycling. The recycling process consists of a cold compaction process, a field-assisted sintering (FAST) process to consolidate the chips, and finally a forward rod extrusion process. Compared to approaches which break the oxide layers by applying high shear stresses and deformations, necessary for an adequate welding of the chips, quasistatic and cyclic properties and capabilities are significantly increased. The defect structure of specimens, which was determined by means of computed tomography and which significantly influences the lifetime, could be correlated well with pre-test electrical resistance measurements. Finally, these findings were used to establish a lifetime calculation model based on unique electrical resistance measurements prior to mechanical testing.
•Field-assisted sintering is a well-suited process to recycle chips.•The quasistatic properties of chip-based specimens exceed the reference.•Fatigue properties in this study exceed conventional recycling approches.•The defect volume determined by CT fits well to electrical resistance measurements.•A lifetime calculation model based on the resistance shows excellent results.
