An AA6061 aluminum alloy tube was fabricated by compacting machining chips via thermomechanical consolidation, including hot pressing and hot extrusion. The microstructure evolution and formation of ...oxide particles were investigated in correlation to tensile mechanical properties. It was found that fine Al/Mg oxide particles were formed due to the fracture of oxide layers on the chips and the reaction between Mg and Al
O
during hot extrusion. The oxide particles inhibited the growth of recrystallized α-Al grains, leading to the formation of a microstructure consisting of coarse elongated grains with sizes of 420 μm and fine equiaxed grains with sizes of 10 μm. After T6 heat treatment, a microstructure with finer grains (grain sizes: 34 μm) formed due to further recrystallization induced by residual strain. The tensile mechanical properties testing results indicated that a good combination of strength (296 MPa) and ductility (7.6%) was achieved in the T6 heat treated samples, which were likely attributed to the high-quality inter-chip bonding, as well as the fine oxide particles which were small enough that further crack nucleation and growth around them were inhibited during tensile deformation. For the purpose of comparison, the microstructure and mechanical properties of the as-extruded and T6 heat treated samples produced by hot extrusion of the cast ingot of AA6061 aluminum alloy were also investigated. The lower tensile strength of solid-state recycled tube sample might be associated with the consumption of Mg atoms by the oxidation reaction, leading to the lower density of β″ precipitates in precipitation strengthening.
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.
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. Precompacted 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 Xray 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.
Al–7Si–0.3Mg (wt%) alloy rods were produced by extrusion of granule compacts at temperatures of 400, 450 and 500°C, respectively. The granules were produced by grinding recycled Al–7Si–0.3Mg ...machining chips. Fracture and redistribution of Si and Al3FeSi particles along the extrusion direction occurred during extrusion, leading to excellent ductility of the consolidated samples with an elongation to fracture ranging from 16.6 to 20.5%, being much higher than that of the Al–7Si–0.3Mg casting alloy. The Al–7Si–0.3Mg alloy rods showed a bimodal size distribution of α-Al grains as a result of recrystallization and growth of new grains. With increasing extrusion temperature from 400 to 500°C, the mean grain size of the α-Al matrix increased from 5.6 to 7.8μm. Meanwhile, rapid establishment of good intergranule bonding was achieved in the Al–7Si–0.3Mg alloy rods during extrusion due to effective breaking of oxide layers on the granules and fast atomic diffusion bonding between the atomically fresh surfaces of the granules.
Recycling of automotive aluminum CUI, Jirang; ROVEN, Hans J.
Transactions of Nonferrous Metals Society of China,
11/2010, Letnik:
20, Številka:
11
Journal Article
Recenzirano
Odprti dostop
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.
A new and promising MMC approach to the reduction of pollution, greenhouse effects, and emissions is to develop a technology related to materials composite forming. Hot extrusion followed by hot ECAP ...is a combination of solid-state recycling method (direct recycling) that consists of chip preparations, cold compaction, and hot extrusion, followed by the ECAP process. The developed process is used to consolidate the chips for direct chip recycling purposes without the remelting phase. In this study, finished or semi-finished products from B4C-reinforced particles and AA6061 aluminium chips were produced. The samples made by hot extrusion were compared with samples obtained from hot extrusion followed by the hot ECAP process in terms of mechanical properties. Additional plastic deformation by hot ECAP after hot extrusion significantly increased the mechanical properties of the MMC compared with the samples obtained from the hot extrusion only. The density and microstructure of the samples were also determined.
The possibility of producing profiles directly by hot extrusion of aluminum chips, normally considered as scrap, is a promising alternative to the energy-intensive remelting process. It has to be ...taken into account that the mechanical properties depend on the quality of the weld seams between the chips, which arise during the extrusion process. To estimate the influence of the weld seams, quasistatic and cyclic investigations were performed on chip-based profiles and finally compared with cast-based extruded profiles. In order to gain comprehensive information about the fatigue progress, different measurement techniques like alternating current potential drop (ACPD)-technique, hysteresis measurements, and temperature measurements were used during the fatigue tests. The weld seams and voids were investigated using computed tomography and metallographic techniques. Results show that quasistatic properties of chip-based specimens are only reduced by about 5%, whereas the lifetime is reduced by about a decade. The development of the fatigue cracks, which propagate between the chip boundaries, was characterized by an intermittent testing strategy, where an initiation of two separate cracks was observed.
Recovering waste metal without the need for remelting in solid-state recycling of metal chips can create green production. The overall process of solid-state recycling should be run at the lowest ...possible cost to remain competitive. High temperature and prolonged preheating time for billet’s homogenization in hot extrusion to consolidate the chips conflicts with the aim of minimizing energy usage. Therefore, optimizing the effect of preheating temperature and time prior to hot extrusion is important. This study investigates the effects of preheating temperature and preheating time on the extrudates’ quality. Milling chips of AA6061 were cold compacted and hot extruded through a flat-face die using preheating temperatures of 400, 500, and 550 °C for 1–6 h of preheating time. The mechanical and physical properties and microstructure of the extruded profiles were compared. The results revealed that higher acceptable strength and ductility were obtained at 500 °C with 2 h of preheating time. On top of that, temperature increase was the main criterion that results in the highest tensile strength; nevertheless, it was subjected to trade-off in ductility. The profile extruded at 500 and 550 °C had gained a close tensile strength. The study includes the prediction of the chip’s welding quality through the damage evolution on the extrudate’s structure. It was implemented with the help of DEFORMTM 3D finite element method (FEM) software, and the normalized Cockcroft and Latham (C & L) fracture criterion was chosen. The results of the simulations were compared and validated by the experimental results.
In this research, a solid-state recycling process of aluminum was performed. It consisted of aluminum EN AW 6082 alloy machining chip cold precompaction and hot extrusion followed by a combination of ...equal channel angular pressing (ECAP) and heat treatment. The main aim of this paper is to determine the fatigue and corrosion behavior of the recycled specimens. In order to determine the recycled specimen fracture mode after fatigue testing, fractography analysis was performed. The corrosion behavior of all specimens was investigated in 0.5 M NaCl solution using open circuit potential measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. It was found that the corrosion resistance of the tested specimens is similar for reference and as-extruded recycled specimens, while it is increased for those which were additionally processed with equal channel angular pressing and heat treatment. Namely, the corrosion current decreased in the same order, while the polarization resistance increased. Impedance measurements have shown that the subsequent plastic deformation and heat treatment of recycled specimens facilitated passivation of tested materials and improved surface film properties, which is confirmed with scanning electron microscopy and energy-dispersive x-ray spectroscopy. Fatigue life was similar for recycled and reference specimens for the selected stress levels. However, fractography showed that multiple cracks appeared inside the recycled specimens which caused different crack propagation mechanisms compared with reference specimens.
Solid-state recycling is a direct conversion method for producing metal chips, whereas the materials are plastically deformed into the final product without melting, offering lower energy consumption ...and metal waste. This technique was reported for fabricating aluminium-zirconium oxide (Al-ZrO2) composite and it was widely used to avoid metal chips bounding at high temperatures during the extrusion process. Aluminium alloy (AA7075) is known for its high yield strength of more than 500 MPa under optimum ageing conditions. However, AA7075 can be further reinforced by zirconium oxide nanoparticles when needed for high-performance applications. Hot extrusion is used to obtain better mechanical properties of composite materials. The equal channel angular pressing (ECAP), a severe plastic deformation technique, was recently used to produce bulk and light recycled metal chips, such as porosity-free and ultra-fine-grained aluminium nanocomposites (ANCs). Heat treatments (HT) and ECAP post hot extrusion are mostly incorporated to improve tribological and mechanical properties and aluminium nanocomposite bonding efficiency. In this review, ANCs’ fabrication by the hot extrusion technique and the effects of ZrO2 nanoparticle are duly summarised and discussed. Furthermore, this review emphasises the importance of using HT and ECAP techniques to acquire better metal alloy incorporation, such as AA7075-ZrO2. Interestingly, owing to the lightweight properties and superior performance of AA7075-ZrO2, it was reported to be suitable for fabricating many drones’ parts, military equipment, and some other promising applications.
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