Key Engineering Materials Vol. 1051

Abstract: Modern manufacturing increasingly demands energy-and resource-efficient solutions. Conventional metal forming often requires high temperatures to reduce flow stress, resulting in high energy consumption, especially for low-formability alloys. Electrically-Assisted Manufacturing (EAM) has emerged as a promising alternative, leveraging the electroplastic effect, i.e. electricity’s direct influence on plastic deformation. Documented benefits include reduced forming forces, improved ductility, and altered fracture modes. Indeed, integrating electroplasticity into manufacturing aligns with Industry 4.0 and decarbonization goals, enabling lower energy consumption, extended tool life, and greater compatibility with renewable energy sources. This study compares conventional tensile testing and electro-assisted tensile testing (EAM) of Ti6Al4V, evaluating both mechanical results and the energy consumption of the testing machine under different conditions. The comparison results highlight the potential of pulsed current to improve material formability while reducing energy consumption, offering a more sustainable approach to manufacturing.

Abstract: Titanium alloys combine strength, low weight, and corrosion resistance, making them vital in high-performance industries; yet machining generates substantial chips that is difficult to recycle via conventional remelting due to contamination and high energy requirements, reducing material sustainability. Solid-state recycling methods, like Shear Assisted Processing and Extrusion (ShAPE), provide a promising alternative by consolidating chips below the melting point while preserving alloy chemistry. This study assesses the environmental performance of ShAPE across a system boundary spanning degreasing through consolidation and extrusion. Impacts were quantified using Cumulative Energy Demand (CED), Global Warming Potential, Environmental Footprint, Average Dissipation Rate (ADR), and Lost Potential Value (LPV), with ADR and LPV applied for the first time to solid-state recycling of scrap from discrete manufacturing. Scenario analyses addressed variations in torque, argon consumption, and electricity mix. Energy demand and CO₂-eq for the ShAPE process were estimated at 279.51-567.75 MJ and 17.22-32.35 kg per kg of wire, respectively, with sensitivity analysis showing that variations in torque constitute the dominant determinant of these environmental outcomes. While energy demand is comparable to, or moderately lower than, that of traditional wire fabrication only under low-and baseline-torque conditions, ShAPE substantially reduces the resource dissipation and lost material values, with its overall environmental impacts further decreasing by 45.45% when powered with greener electricity. These results highlight ShAPE as a viable route for circular titanium production, preserving material value & reducing dependence on primary extraction.

Abstract: This study evaluates the processability of recycled polypropylene (rPP) in pellet-based material extrusion (MEX) to support more sustainable additive manufacturing. Virgin polypropylene (PP) and post-consumer rPP obtained from end-of-life woven builder bags were processed in neat form and as PP/rPP blends with increasing recycled content. Melt-flow behavior was characterized using a Technological Melt Flow Index (TMFI), a process-specific metric reflecting the combined effects of temperature and screw rotation. Disk-shaped specimens were printed to assess deposition behavior through the build-up rate (BUR), which integrates shear flow in the extruder and elongational deformation during deposition. TMFI results show that rPP exhibits markedly higher flowability than virgin PP below 200°C, indicating potential for lower-temperature, energy-efficient processing. In contrast, printing experiments reveal that BUR systematically decreases with increasing rPP content. This trend indicates a transition to an elongation-dominated deposition regime, where rPP displays higher resistance to extensional deformation during deposition, resulting in narrower roads and reduced spreading. Regression analysis confirms that BUR is governed primarily by flow-rate setting (F%) and nozzle speed (Sp%), whereas nozzle temperature Te (°C) has only a minor influence within the investigated window. Overall, the results demonstrate the competing rheological effects introduced by recycling and highlight the need for tailored parameter optimization to enable higher rPP incorporation in pellet-based 3D printing.

Abstract: The use of composite materials and specifically of Fiber Reinforced Polymers (FRP) is continuously increasing in structural applications due to their high strength-to-weight ratio. From an environmental perspective, composites still face relevant challenges due to impactful petroleum-based matrices and large amounts of waste generated during manufacturing processes. This study proposes the reuse of FRP machining waste as filler in Masked Stereolithography (M-SLA) 3D printing. Scraps from FRP laminates, obtained during drilling operations, were incorporated into a photocurable resin and used to print tensile and flexural specimens with increasing filler contents (0–5 wt%) and mechanical characterization tests were carried out. A cradle-to-grave Life Cycle Assessment (LCA) was performed to quantify the potential environmental benefits associated with the reduced use of virgin resin. Results show that the use of recycled FRP waste leads to a loss of tensile strength and stiffness (up to 61% and 21% respectively) but it also provides a reduction in Global Warming Potential (about 2% at 5 wt% filler). This demonstrates that the proposed strategy can improve the sustainability of 3D-printed components, especially for non-structural applications.

Abstract: Recycling aluminum chips remains a major challenge in aluminum manufacturing because it is difficult to retain the original quality alloy properties while reducing the carbon footprint and ensuring a sustainable process. This work investigates the microstructural evolution and bonding quality of compacted AA6082 chips processed through friction extrusion/consolidation. The residual material left inside the extrusion container after processing at a high extrusion ratio was analyzed using SEM, EDS, and EBSD to understand bonding mechanisms and microstructure evolution in front of the die. The SEM results show that voids are still present between the chips in the initial compacted material which already shows bonding, while these voids are reducing towards the die interface, particularly related to the present severe plastic deformation. EDS analysis confirms the presence of Al (Fe,Mn)Si intermetallic particles, which break and disperse in the matrix because of shear deformation due to die rotation. EBSD analysis reveals that grains are coarser near the base material, and subdivisions of grains near the die interface are significant because of continuous dynamic recrystallization.

Abstract: The most common structural material used in the construction sector is steel-reinforced concrete. However, concrete cracking and reinforcement corrosion demand constant monitoring as well as timely and costly maintenance activities. Furthermore, concrete has substantial environmental impacts, being responsible for about 7% of total CO₂ emissions worldwide. Innovative materials in construction engineering have been studied with the goal of improving the sector’s environmental performance, mostly by reducing cement content in concrete. In this context, assessing the environmental profile of such innovations is essential to avoid shifting environmental burdens elsewhere. This study evaluates the climate change impact of a novel reinforced concrete that incorporates calcined blue clay as a supplementary cementitious material and Aluminium (Al) as reinforcement. Using a cradle-to-gate Life Cycle Assessment (LCA), the climate change impact of this innovative material is compared with that of conventional steel-reinforced concrete. The result show that the climate change impact of the innovative concrete is 46% less than that of the incumbent solution. Acknowledging the early development stage of the new concrete and the limitation regarding data robustness, this work contributes to the problem-solution space and provides direction to further explore possibilities for fully unlocking the new material’s potential, so it can outperform the incumbent one in terms of greenhouse gas emissions in the future.

Abstract: The growing demand for high-performance, sustainable micro-moulded components requires integrated approaches to material and process selection. The study presents a Life Cycle Engineering (LCE) framework for the integrated selection of materials and manufacturing technologies for micro-injection molds, combining Life Cycle Assessment (LCA), Life Cycle Costing (LCC), and multi-criteria decision models. The methodology implements multicriteria cost impact maps and ternary LCA–LCC–technical performance model, allowing for result normalization and sensitivity analysis with respect to criterion weighting. The framework is applied to molds fabricated from steel, aluminium alloy, polyether-ether-ketone (PEEK), and high-temperature resin, using both subtractive and additive processes, with topological optimization. Mass reductions of up to 22% achieved through optimization translate into cost and environmental impact savings of 30–45% during production and use phases, although with potential service life reductions of up to 50% for polymeric materials. LCA and LCC analyses highlight production and use as the dominant life cycle phases, with end-of-life (EoL) impacts being comparatively minor. Sensitivity analysis shows that: (i) cost-prioritized scenarios select optimized steel molds; (ii) scenarios prioritizing lightweight design and environmental performance select advanced polymers and additive manufacturing; (iii) balanced scenarios identify PEEK as the optimal solution. The proposed framework enables the concurrent selection of material and technology aligned with design objectives and geometric optimization, providing quali-quantitative support for sustainability-oriented industrial decision-making across the life cycle.

Abstract: Aluminum components production is associated with significant greenhouse gas emissions due to both raw material extraction and energy-intensive manufacturing processes. In particular, the melting phase required high thermal energy and conventional energy sources (e.g. fossil fuels, national grids...) can result in relevant environmental impacts. This study evaluates the environmental sustainability of four different energy supply systems for aluminum die casting through a comparative Life Cycle Assessment (LCA). Four scenarios were analyzed: natural gas, national grid electricity, photovoltaic (PV) electricity with battery storage, and PV-powered hydrogen production with metal-hydride storage. A cradle-to-gate approach was adopted, including energy production, storage, raw materials extraction, tool manufacturing, casting operations and finishing. The environmental impacts were modelled using SimaPro, and Global Warming Potential (GWP) was calculated according to the Intergovernmental Panel on Climate Change (IPCC) methodology. The results show that renewable-based solutions represent the most sustainable alternatives, with impact reductions up to 62% compared with traditional approaches. PV electricity with battery storage achieves the lowest unitary impacts (0.15 kg CO₂ eq/kWh). Hydrogen produced from PV electricity also provides significant reductions relative to natural gas and grid electricity and offers high operational flexibility. The metal-hydride storage system shows slightly lower impacts than battery storage, due to its long service life and minimal hydrogen losses. These results highlight the potential of renewable energy and green hydrogen as alternative energy carriers for industrial production.

Abstract: Increasing scrap usage in steelmaking is vital for resource efficiency and CO₂ reduction, but elevated residual copper limits adoption due to hot shortness during hot forming. Conventional continuous casting promotes Cu segregation in interdendritic regions, and subsequent slab reheating accelerates oxidation-driven Cu enrichment at the steel–scale interface, where liquid Cu penetrates grain boundaries and weakens cohesion. Twin-roll casting (TRC) offers a promising alternative, as its high solidification rates suppress Cu segregation and its near-net strip production eliminates slab reheating and minimizes oxidation. In this work, the hot-shortness resistance of a 0.75 wt.% Cu construction steel processed by TRC is evaluated and directly compared with a conventionally cast and reheated counterpart. The comparison reveals that TRC effectively mitigates copper-related damage mechanisms. Cu remains primarily in the thin scale without penetrating the substrate, enabling hot rolling and downstream processing without cracking. In contrast, the conventional route forms a thick, brittle, Cu-rich scale that promotes grain-boundary penetration and severe hot shortness. Overall, TRC expands the allowable copper content in flat steel production and broadens alloy design opportunities for scrap-based steelmaking.