Search Results (89)

This study investigates the quasi-static axial crushing behaviour of carbon fibre-reinforced polymer (CFRP) tubes with variations incorporating polyurethane foam (PU) and aluminium tubes. Six different composite configurations were fabricated, including a baseline hollow CFRP tube and hybrid structures with foam and aluminium reinforcements. The mechanical response was evaluated through load–displacement behaviour and energy absorption. Visual inspection of the failure modes revealed distinct fracture mechanisms influenced by the type of reinforcement. The results indicate that incorporating aluminium significantly enhances load-bearing capacity, energy absorption, and crushing efficiency, with the sample containing four aluminium secondary tubes exhibiting the highest specific energy absorption. Meanwhile, foam-filled samples improved load-bearing capacity while mitigating brittle failure. These findings suggest that CFRP hybrid structures with aluminium and foam reinforcements offer promising solutions for lightweight Crashworthiness applications in the automotive and aerospace industries. Full article

Large functionally integrated casting and electrification are rapidly changing the high-pressure die-casting industry. The requirements for these new castings differ from those of the previous ones. Load-bearing capability, fatigue, ductility, and crashworthiness all increase, and the foundry’s readiness for this varies and is challenging. At the same time, the carbon footprint needs to be reduced, meaning that recycled, secondary aluminium usage is required, making the challenge of attaining the required component performance significantly more difficult. The current paper examined the conditions and requirements to manage and reach the required targets, both from a material standpoint as well as from a climate impact and resource-efficiency perspective. Full article

This study examines the potential for improved and more sustainable wastewater treatment by integrating coagulation and disinfection using polyaluminum chloride (PACl) and sodium hypochlorite (NaClO) for secondary effluent. The impacts of this integrated approach on phosphorus removal, microbial inactivation, and disinfection by-product (DBP) formation were evaluated through bench- and pilot-scale experiments under both sequential and simultaneous dosing. The results show that simultaneous dosing of PACl and NaClO achieved high phosphorus removal (>90% at 6–9 mg/L PACl), while microbial inactivation targets were met with moderate chlorine doses (3–6 mg/L). Pilot-scale tests further revealed that PACl enhanced microbial inactivation under high-intensity mixing. Importantly, the integrated process reduced DBP formation substantially, with trihalomethanes (THMs) and haloacetic acids (HAAs) lowered by up to ~50% compared to sequential treatment. By minimizing the need for separate treatment units, shortening hydraulic retention time, and lowering overall chemical consumption, this integrated coagulation–disinfection strategy provides a compact, cost-effective, and sustainable alternative to conventional wastewater treatment. Full article

Aviation’s sustainability discourse often centres on flight emissions, but production and end-of-life phases also carry material, energy, and pollution impacts that are large enough to merit systematic intervention. With ~13,000 aircraft projected to retire over the next two decades—roughly 44% of the global fleet—the sector must scale responsible dismantling and material recovery to avoid lost opportunities for meeting future sustainability goals and to harness economic value from secondary parts and recycled feedstocks. Embedding major sustainability and circular economy principles into aircraft design, operations, and retirement can reduce waste, conserve critical materials, and lower lifecycle emissions while contributing directly to multiple SDGs. Furthermore, when considering particular aircraft types, thousands of narrow-body aircraft such as the Airbus A320 and Boeing 737 are due to reach their end of life over the next two decades. This research evaluates the economic and environmental feasibility of aluminium recycling from these aircraft, integrating material flow analysis, cost–benefit modelling, and a lifecycle emissions assessment. An economic assessment framework is developed and applied, with the results showing that approximately 24.7 tonnes of aluminium can be recovered per aircraft, leading to emissions savings of over 338,000 kg of CO₂e, a 95% reduction compared to primary aluminium production. However, scrap value alone cannot offset dismantling costs; the break-even scrap price is over USD 4200 per tonne. When additional revenue streams such as component resale and carbon credit incentives are incorporated, the model predicts a net profit of over USD 59,000 per aircraft. The scenario analysis confirms that aluminium recycling only becomes financially viable through multi-stream revenue models, supported by Extended Producer Responsibility (EPR) and carbon pricing. While barriers remain, aluminium recovery is a strategic opportunity to align aviation with circular economy and decarbonisation goals. Full article

The rising demand for aluminium and environmental concerns highlight the need for a circular economy using recycled alloys. This study examines the effect of shot peening on the high-cycle fatigue life of secondary AlZn10Si8Mg alloys with different iron contents: Alloy A (0.14 wt.% Fe) and Alloy B (0.56 wt.% Fe). Although both alloys showed similar tensile properties, Alloy B had higher porosity and finer β-Al₅FeSi intermetallics. Shot peening was applied at 100% and 1000% coverage to evaluate changes in surface roughness, porosity, residual stresses, and fatigue performance. The treatment significantly reduced surface-connected porosity via plastic deformation, enhancing fatigue life despite increased roughness. Fatigue tests showed a 21% increase in fatigue limit for Alloy A and a 6% gain for Alloy B at higher coverage. Fractographic analysis revealed that 95% of fatigue cracks initiated at surface pores. Residual stress measurements confirmed compressive stresses were limited to the near-surface layer, with minimal influence on subsurface crack propagation. Overall, shot peening proves to be an effective method for improving fatigue resistance in recycled aluminium alloys, even in alloys with elevated iron content, reinforcing their potential for structural applications under cyclic loading. Full article

Geopolymer composite materials are a viable alternative to conventional construction materials. The research problem of geopolymer composites revolves around the imperative to comprehensively address their synthesis, structural performance, and environmental impact. The derived mathematical model facilitates precisely determining the optimal proportions of two crucial constituents in the geopolymer matrix: silica sand and secondary aluminum by-product. A mathematical model for optimizing the composition of geopolymer composites has been developed based on the integrated use of Markov chains, criterion methods, and an orthogonally compositional plan. The optimal composition of the geopolymer matrix is determined and predicted using a mathematical model. Specifically, the recommended content mixing ratio is as follows: metakaolin at 1000 g, activator at 900 g, silica fume at 1052.826 g, carbon fibre at 10 g, and secondary aluminum by-product at 62.493 g. This study analyzes the influence of different secondary aluminum industry by-products on the geopolymerization process and assesses the mechanical, thermal, and environmental properties of the resulting composites to establish a comprehensive understanding of their structural viability. Full article

Epidemiological analysis has revealed key insights into the frequency, severity, and circumstances surrounding subway-to-pedestrian incidents; however, there remains a lack of available impact test data specific to this impact type that can be used in modelling and countermeasure design studies. To address this gap, nine controlled impact tests were conducted using a cylindrical headform to derive force–penetration relationships for foam, as well as foam encased in 1 mm aluminium or 3 mm ABS shells. These relationships were validated in MADYMO multibody simulations. Building on a previous multibody computational study of subway-to-pedestrian collisions this research evaluates three passive countermeasure designs using a reduced simulation test matrix: three impact velocities (8, 10, and 12 m/s) and a trough depth of 0.75 m. In subway collisions, due to the essential rigidity of a subway front relative to a pedestrian, it is the pedestrian stiffness characteristics that primarily dictate the contact dynamics, as opposed to a combined effective stiffness. However, the introduction of energy-absorbing countermeasures alters this interaction. Results indicate that modular energy-absorbing panels attached to the train front significantly reduced the Head Injury Criterion (HIC) (by 90%) in the primary impact and pedestrian-to-wheel contact risk (by 58%), with greater effectiveness when a larger frontal area was covered. However, reducing primary impact severity alone did not substantially lower total fatal injury risk. A rail-guard design, used in combination with frontal panels, reduced secondary impact severity and led to the largest overall reduction in fatal injuries. This improvement came with an expected increase in hospitalisation-level outcomes, such as limb trauma, reflecting a shift from fatal to survivable injuries. These findings demonstrate that meaningful reductions in fatalities are achievable, even with just 0.5 m of available space on the train front. While further development is needed, this study supports the conclusion that subway-to-pedestrian fatalities are preventable. Full article

Semi-solid processes of aluminium alloys, characterised by the coexistence of solid and liquid phases, offer advantages in terms of mechanical properties and fatigue resistance, thanks to the more globular microstructure. Thermodynamic models can be used to analyse the solidification behaviour and to predict the solidification window, ΔT. The CALPHAD method enables the calculation of the phases formed during solidification and the optimisation of alloy composition to meet specific industrial requirements. This study aims to assess how thermodynamic properties in both liquid and solid phases affect the ΔT. Initially, the influence of thermodynamic properties of pure components and interaction parameters was analysed in simplified regular binary systems. To compare these findings with real industrial systems, Al-based alloys were examined. Using available databases, the ΔT was estimated via the CALPHAD method adding alloying elements commonly found in secondary Al-alloys. Finally, the same minority alloying elements were added to Al-Si 8 and 11 wt.% alloys, and the corresponding ΔT were calculated. Cr, Fe, Mg, Mn, and Ti increase the ΔT, while Cu, Ni, and Zn decrease it. The obtained results may serve as a valuable tool for interpreting phenomenological observations and understanding the role of minority elements in the semi-solid processing of secondary Al-Si casting alloys. Full article

The amount of secondary aluminium dross in China exceeds one million tons annually, posing environmental and disposal challenges. This study explores acid leaching as an alternative to conventional alkali methods for recovering Al from secondary aluminium dross to produce Al₂O₃. Research has focused on optimizing leaching conditions. Under optimized H₂SO₄ leaching conditions, an Al³⁺ leaching ratio of 86.5% is achieved. By maintaining a pH below 9 during hydrolytic precipitation and multiple washes, the leaching efficiency of Al from Al(OH)₃ reached 95.97%. The original dross, which is primarily composed of Al, Al₂O₃, and AlN, undergoes a transformation where AlN becomes Al(OH)₃ during washing. Thermal decomposition then yields Al₂O₃. The overall recovery of Al reaches 83.11%. Full article

The characterisation of aluminium casting alloys with iron concentrations exceeding current standards is essential, as upcycling has recently become a significant concern in achieving a more circular economy. Secondary aluminium casting alloys often exhibit insufficient mechanical properties for load-bearing automotive applications due to contamination with iron, mainly due to alloy mixing or remnants from end-of-life products during downcycling. This trend is anticipated to soon lead to a surplus of scrap. This study aims to fully understand the microstructural changes, intermetallic phase morphologies, and defect formation in AlSiMg alloy highly contaminated with Fe that exists in Al scraps and is detrimental for upcycling purposes. The investigation examined the AlSi7Mg0.3 alloy with Fe concentrations ranging from 0.1 to 3.8 wt.% Fe, employing thermodynamic simulations, hardness testing, quantitative image analysis, and corrosion tests. Among these alloys, the AlSi7Mg0.3-3.8Fe, containing the highest level of contamination, exhibited the most complex microstructure. This microstructure is characterised by the presence of two distinct Fe-rich intermetallic phases with diverse shapes and sizes: petal-like α′-Al₈Fe₂Si, long and thick β-Al_4.5FeSi plaques, and very thin β-Al_4.5FeSi needles. The significant growth in these phases with higher Fe concentration resulted in increases in hardness (15 HBW), porosity (1.39%), and corrosion rate (approximately 12 times). Full article

In this work, we intended to study the effect of heat treatments (T5 and flash T6) on blistering, mechanical properties and microstructure for different parts produced by vacuum-assisted HPDC. These parts were produced with primary and secondary aluminium alloys (AlSi10MnMg alloy and AlSi10Mg(Fe) alloy, respectively). The parts presented blisters for all combinations of temperature (between 360 °C and 520 °C) and stage times (15 and 30 min) of solution heat treatments. However, when subjected to the T5 heat treatment, blisters were no longer visible. With this heat treatment, there was an increase in yield strength of 64% for both aluminium alloys and an increase in UTS of 31% in AlSi10Mg(Fe) alloy and of 24% in AlSi10MnMg alloy, when compared to the mechanical properties in the as-cast state. However, there was a decrease in ductility. The AlSi10Mg(Fe) alloy presented a lot of contaminations (especially iron), which impaired the mechanical properties compared to the primary aluminium alloy, AlSi10MnMg. Full article

In recent years, the demand for natural and synthetic zeolites has surged due to their distinctive properties and myriad industrial applications. This research aims to synthesise crystalline zeolites by co-recycling two industrial wastes: salt slag (SS) and rice husk ash (RHA). Salt slag, a problematic by-product of secondary aluminium smelting, is classified as hazardous waste due to its reactive and leachable nature, though it is rich in aluminium. Conversely, RHA, an abundant and cost-effective by-product of the agro-food sector, boasts a high silicon content. These wastes were utilised as aluminium and silicon sources for synthesising various zeolites. This study examined the effects of temperature, ageing time, and sodium concentration on the formation of different zeolite phases and their crystallinity. Results indicated that increased Na⁺ concentration favoured sodalite (SOD) zeolite formation, whereas Linde type–A (LTA) zeolite formation was promoted at higher temperatures and extended ageing times. The formation range of the different zeolites was defined and supported by crystallographic, microstructural, and morphological analyses. Additionally, the thermal behaviour of the zeolites was investigated. This work underscores the potential to transform industrial waste, including hazardous materials like salt slag, into sustainable, high-value materials, fostering efficient waste co-recycling and promoting clean, sustainable industrial production through cross-sectoral industrial symbiosis. Full article

Diatomite, a natural adsorbent rich in active silica, serves as a valuable precursor for geopolymer synthesis. The safe disposal of diatomite as a failed lead (Pb(II)) adsorbent is critical to prevent secondary contamination. This study investigated the immobilisation efficiency of geopolymerisation for Pb(II)-rich diatomite sludge. Low-grade diatomite with high ignition loss was utilised in the synthesis of alkali-activated geopolymers. It was demonstrated that the geopolymers achieved a compressive strength of 28.3 MPa with a 50% replacement rate of metakaolin by diatomite sludge, which was not a compromise in strength compared to that of the geopolymer with no Pb(II) (26.2 MPa). The leaching behaviour of Pb(II) was evaluated using water and acetic acid, yielding concentrations below 3 mg/L and immobilisation efficiencies of 95% in both scenarios. Analytical techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) elucidated the mineral composition and chemical environment of the geopolymers. These analyses revealed that Pb(II) migrated from diatomite pores, potentially forming soluble hydroxides under sufficient hydroxide, which then participated in condensation with silicon and aluminium monomers, effectively immobilising Pb(II) within amorphous aluminosilicate gels. Furthermore, the formation of the amorphous gels within diatomite pores hindered Pb(II) leaching, encapsulating Pb(II) effectively. This study presents a novel approach to immobilising heavy metals within building materials, enhancing mineral resource utilisation efficiency while addressing environmental contamination concerns. Full article

Aluminium alloys have a wide range of applications, mainly due to their advantageous strength-to-weight ratio, denoted as specific strength and corrosion resistance. In recent decades, there has been a notable surge in the usage of recycled alloys, attributed to their reduced production costs and emissions. One of the conditions for secondary production is the optimal sorting of used scrap. Once the aluminium scrap has been melted, it is tough to reduce the content of the various additives. Copper is the primary alloying element in some aluminium alloys, which leads to an increased amount of copper in the aluminium scrap. Therefore, it is important to investigate its effect on the properties of aluminium alloys in which it is not commonly present. For this reason, this paper is concerned with the influence of copper on the microstructure and properties of the secondary aluminium alloy AlZn10Si8Mg. Specifically, it compares two melts of self-hardening AlZn10Si8Mg alloys differing in copper content (0.019% and 1.72%). A complex quantitative and metallographic analysis by optical and electron microscopy has been performed. Mechanical properties were investigated by tensile test, Brinell hardness, and Vickers microhardness measurements. The corrosion resistance of the individual melts was verified by the Audi test. Full article

Additive friction stir deposition (AFSD), in which molten metal materials are formed into free-form stacked structural parts according to the path design, may have a wide range of applications in high-efficiency mass production. In this study, experiments were conducted for the rotational speed in the AFSD parameters of 6061 aluminium alloy bars to investigate the effects of different rotational shear conditions and heat inputs on the properties of the deposited layer for diameter bars based on the analysis of the micro-morphology, micro-tissue composition, and mechanical properties. The width and thickness of each layer were constant, approximately 40 mm wide and 2.5 mm thick. The particle undulations on the surface of the deposited layer were positively correlated with the AFSD rotational speed. Continuous dynamic recrystallisation in the AFSD process can achieve more than 90% grain refinement. When the rotational speed increases, it causes localised significant orientation and secondary deformation within the recrystallised grains. The ultimate tensile strength of the deposited layer was positively correlated with the rotational speed, reaching a maximum of 211 MPa, and the elongation was negatively correlated with the rotational speed, with a maximum material elongation of 37%. The cross-section hardness of the deposited layer was negatively correlated with the number of thermal cycles, with the lowest hardness being about 45% of the base material and the highest hardness being about 80% of the base material. Full article