Scrap Streams Research Articles

Benchmarking wire-fed and autogenous laser beam welding to study the effect of Cu additions on weld integrity of 6060-T6 aluminium extrusion

In the automotive industry 6xxx aluminium alloys are preferred materials, yet their fabrication contributes to a considerable carbon footprint. A promising strategy to mitigate the environmental impact is the increased utilisation of recycled (secondary) aluminium, sourced from diverse scrap streams. However, as aluminium scraps come from different sources, the intrinsic variability of chemical composition, stemming from uncontrollable levels, poses a challenge, impacting material properties and weldability. Balancing manufacturability while enhancing the adoption of recycled alloys becomes a critical effort. This study aims at benchmarking wire-fed and autogenous laser beam welding to study the effect of Cu inclusions on weld integrity of 6060-T6 extrusion. The paper contributes to show the impact of Cu addition during laser welding of 6060-T6 aluminium alloys. Findings highlighted that the modification of chemical composition using filler wires is currently the most efficient approach to improve joint strength, although the Cu additions tend to reduce the weld strength.

Hydrogen-assisted recycling of Nd-Fe-B magnets from the end-of-life audio products

The transition towards green and sustainable technologies has significantly increased the demand for a subset of raw materials known as critical elements. Rare earth elements with their main use in Neodymium-Iron-Boron magnets (NdFeB) play a key role in clean energy technologies including electric vehicles and wind turbine generators. They are also a key component in electronic devices including mobile phones, hard disk drives, and loudspeakers. Here, we build on previous knowledge of the recycling of NdFeB magnets from hard disk drives, using a hydrogen process called HPMS (Hydrogen Processing of Magnet Scrap). This study investigates a new scrap stream from loudspeakers, specifically from vehicles and flat-screen TVs. The extracted magnets from loudspeakers typically had grades of N30/N33 with relatively low coercivity values. The interactions of the extracted magnets with hydrogen were monitored by gravimetric and thermal analyses. The thermodynamics and kinetics of the hydrogenation reaction appear to differ significantly based on their chemical composition, chemical homogeneity, coating state, and surface condition of the magnets. Overall, the HPMS process was demonstrated to successfully produce demagnetised hydrogen decrepitated powder at room temperature under 2 bar of hydrogen, in a commercially viable timeframe (approx. 4 h). Zinc was found to be the dominant coating material which peeled away during the HPMS process. The zinc content of the NdFeB alloy powder could be reduced after the hydrogen decrepitation by sieving. The remaining level of zinc had no noticeable impact on the magnetic properties of the recycled magnets. The particle size of the recycled alloy powder could be reduced to below 7 µm by ball milling and knife milling but with an increase in the oxygen level, limiting its sintering ability. Sintered magnet from the recycled alloy powder demonstrated similar magnetic properties (Br: 1.06 T, HcJ: 1240 kA/m, and (BH)max: 220 kJ/m3) after blending with 5 wt% of NdH3, making vehicles and flat-screen TV speakers ideal sources for a recycled magnet.

The coming wave of aluminum sheet scrap from vehicle recycling in the United States

The emergence of mass-produced aluminum sheet intensive vehicles presents an opportunity for recyclers to shift towards high value recycling into wrought alloys. We use dynamic material flow analyses (2015–2050) to estimate the timing, scale, and composition of U.S. aluminum automotive body sheet (ABS) scrap generated from the aluminum ABS intensive vehicles with the highest U.S. sales: Ford F-150, Super Duty, Expedition, and Lincoln Navigator. Lifespan distribution models are derived for each vehicle, and 5xxx and 6xxx series sheet alloys are aggregated according to their copper and magnesium content. A Markov chain model is used to estimate the fraction of deregistered vehicles scrapped domestically versus exported.It is found that the above four vehicles account for around 1,200 kt of aluminum ABS embedded within the 2020 U.S. fleet. The aluminum ABS intensive construction of these vehicles presents a unique opportunity to U.S. recyclers. If production continues at the current volumes, aluminum ABS scrap from these vehicles will increase to approximately 125 kt/year in 2035 and 246 kt/year in 2050. The majority of this scrap will be available for U.S. processing with <<10% of deregistered vehicles exported or achieving vintage status. For comparison, only 121 kt of aluminum auto shred (containing negligible aluminum ABS) was domestically consumed in the U.S. in 2017. We analyze the composition of the future potential scrap streams, revealing the need for alloy separation and tramp element removal if closed loop aluminum ABS recycling is to be achieved.

Evaluating the material resource efficiency of secondary aluminium production: A Monte Carlo-based decision-support tool

The contamination of aluminium streams during the different life cycle stages by alloy mixing and/or accumulation of foreign elements, in combination with the limited melt purification options during remelting, represents an important limiting factor in recycling. Consequently, in secondary aluminium production, primary aluminium is used to dilute the concentration of the residual elements, and alloying elements are added to adjust the composition to the target alloy specifications. However, adding elements, for which their refinement in a subsequent recycling step is problematic, results in permanent down-cycling or ‘quality losses’. Hence, it is crucial to more efficiently control the composition of the metal streams prior to remelting. This article focuses on the aluminium cascade recycling chain and presents a Monte Carlo-based decision-support tool aiming to: i) identify all feasible clustering solutions per case based on input/output analysis; ii) quantify their environmental effect, and analyze the trade-offs; iii) consider scrap composition uncertainty/variability. Results reveal that primary resource additions can be minimized by optimizing metal sorting, and thus closing the recycling loop more effectively. Case studies are presented to illustrate the different functions of the tool, including examination of the Pareto front, and evaluation of the ‘recyclability’ of a scrap stream or a sorting solution into different alloy systems.

Environmental screening of novel technologies to increase material circularity: A case study on aluminium cans

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.

Environmental modelling of aluminium recycling: a Life Cycle Assessment tool for sustainable metal management

The uncontrolled mixing of metals and their alloys during the different life cycle phases, combined with the melt purification constraints during remelting, pose great challenges during their end-of-life (EoL) treatment. In practice, open-loop recycling is typical and more common for metals than closed-loop recycling; especially in the case of aluminium, the industry operates in a cascade recycling approach. Associated with open-loop recycling are various types of material losses; loss of original functional quality, dissipation of scarce resources and the final need for dilution of the resulting metal impurities with primary materials. Thus, an environmental assessment tool is presented within this paper, aiming to support decision making related to the sustainable management of metal resources during secondary aluminium production. A material blending model aims at the minimization of the above mentioned losses in order to meet the product quality requirements. The goal of the study is threefold: i) to assess the environmental impact calculation of aluminium recycling, ii) to express, quantify and integrate dilution and quality losses into Life Cycle Assessment (LCA) studies, and iii) to determine the optimum material input for the recycling process from an environmental perspective. Different recycling options or strategies can be evaluated and compared based on avoided environmental impact. Case studies focusing on major post-consumer scrap streams are used to illustrate application areas and highlight the importance of altering and optimizing the raw material input. Finally, policy issues and opportunities for environmentally conscious metal management are discussed.

Modeling of Alternative Compositions of Recycled Wrought Aluminum Alloys

Nowadays, a significant part of postconsumed wrought aluminum scrap is still used for the production of comparatively cheaper cast alloys, in that way losing an important part of the potential added value. The share of postconsumed scrap in wrought aluminum alloys could be increased either by sorting to fractions with the required chemical composition and/or by broadening the standard compositional tolerance limits of alloying elements. The first solution requires hand or automatic sorting of postconsumed scrap as alloys or groups of alloys to the degree of separation sufficient to enable the blending of standard compositions of wrought alloys; the second solution is much more radical, predicting changes in the existing standards for wrought aluminum alloys toward nonstandard alloys but yet having properties acceptable for customers. In this case, the degree of separation of incoming postconsumed scrap required is much less demanding. The model presented in this work enables the design of optimal (standard and nonstandard recycling-friendly) compositions and properties of wrought aluminum alloys with significantly increased amounts of postconsumed scrap. The following two routes were modeled in detail: (I) the blending of standard and nonstandard compositions of wrought aluminum alloys starting from postconsumed aluminum scrap sorted to various degrees simulated by the model and (II) changing the initial standard composition of wrought aluminum alloys to nonstandard “recycling-friendly” ones, with broader concentration tolerance limits of alloying elements and without influencing the selected alloy properties, specified in advance. The applied algorithms were found to be very useful in the industrial design of both procedures: (I) the computation of the required chemical composition of the scrap streams obtained by sorting (or, in other words, the postconsumed scrap sorting level), necessary for achieving the standard wrought alloy composition and (II) the transformation of standard to nonstandard (recycling-friendly) compositions with the key alloy properties (e.g., tensile strength and elongation) remaining the same.

Toward Sustainable Material Usage: Evaluating the Importance of Market Motivated Agency in Modeling Material Flows

Increasing recycling will be a key strategy for moving toward sustainable materials usage. There are many barriers to increasing recycling, including quality issues in the scrap stream. Repeated recycling can compound this problem through the accumulation of tramp elements over time. This paper explores the importance of capturing recycler decision-making in accurately modeling accumulation and the value of technologies intended to mitigate it. A method was developed combining dynamic material flow analysis with allocation of those materials into production portfolios using blending models. Using this methodology, three scrap allocation methods were explored in the context of a case study of aluminum use: scrap pooling, pseudoclosed loop, and market-based. Results from this case analysis suggest that market-driven decisions and upgrading technologies can partially mitigate the negative impact of accumulation on scrap utilization, thereby increasing scrap use and reducing greenhouse gas emissions. A market-based allocation method for modeling material flows suggests a higher value for upgrading strategies compared to a pseudoclosed loop or pooling allocation method for the scenarios explored.

Compatibilization strategies for upgrading recycled plastics performance: Use of reactive rubbery polymers

One of the inherent problems in the recycling of polymers involves the wide variety of immiscible and incompatible polymer resins. For this reason, it is important to keep scrap from different sources separate, especially if it is known beforehand that the compositions are significantly different. Approaches to upgrading the performance of the scrap streams can then be tailored to each stream. Our work has been based, in part, upon one such approach. Reactive rubbery polymers have been used to modify several recycle streams. These models represent household scrap, business machine housings, and automobile bumpers. Dramatic property improvements can be obtained if specific reactive rubbery polymers are matched to certain recycle streams. Also, it was found that variability in the source and the composition of a given stream over time can dramatically affect results. These findings underscore the inherent difficulty in developing a universal approach to the recycling of mixed plastics.