Papers by Keyword: Secondary Aluminium

Abstract: The decarbonization of the aluminium industry requires a transition from fossil fuels to sustainable energy carriers. This study investigates the substitution of natural gas (NG) with hydrogen (H₂) in reverberatory furnaces, analyzing the impact on melt quality, furnace integrity and exhaust emissions. Experimental investigations were conducted in a specifically designed furnace setup combining electrical heating with a burner system capable of operating with variable fuel blends ranging from pure natural gas to 100 vol.-% hydrogen. The results demonstrate that the hydrogen content in the aluminium melt depends on the atmospheric conditions — water vapour content in the atmosphere — during the melting and heating phases. In contrast, the holding phase exhibited a quasi-static behavior with negligible further hydrogen uptake, due to the isothermal process control. Numerical simulations (CFD) revealed that admixture rate exceeding 80 vol.-% H₂ leads to significantly higher adiabatic flame temperatures. This results in the formation of local hotspots on the furnace walls and requiring the use of high-performance refractory linings. Furthermore, these thermal conditions correlated with a major increase in NO_x emissions, despite a successful reduction in CO₂ output. Considering the material quality, X-ray computed tomography (XCT) analysis indicated a marginal increase in volume porosity with higher hydrogen fractions. However, tensile testing confirmed that this porosity did not compromise the mechanical performance, as yield strength and ultimate tensile strength remained unaffected across all fuel mixtures. The study concludes that standard degassing procedures are sufficient to reduce the increased initial hydrogen load, showing that hydrogen combustion for secondary aluminium production is feasible.

Abstract: Structural high vacuum die casting has been growing significantly over the past decades. It is typically done with special (primary type) alloys, special melt treatment practices, high vacuum, a carefully engineered die casting process applying many best practices in our industry. Structural die castings are growing in size and complexity and die casting machines are getting bigger and bigger - and those castings are becoming a significant challenge with current technologies. It was now found that Rheocasting - a process of preparing a semi-solid slurry (with 30-45% solid fraction) that is injected slower and in a laminar way into the cavity, can take structural die casting to completely new heights, enable the casting of parts that would otherwise be impossible to cast and at the same time reduce or eliminate some of the current problems of structural die casting. With Rheocasting, lower purity (secondary) aluminum alloys can be used and excellent properties can be achieved as cast and heat treated (T5, T6/7). Rheocasting has had a breakthrough in the telecom and other industries, but it has now been optimized to become an essential tool in the toolbox of making structural castings. This paper shows the developments that lead to the successful series production of a large (about 4’ long) hinge pillar for an Electric Vehicle (EV). It explains the challenges and how they were overcome, and some of the possibilities of the process regarding alloys, heat treatments and achievable properties. It also shows how Rheocasting can help die casters produce more complex (thin and thick walled) and very large castings with the highest integrity. It can replace structural low-pressure permanent mold (LPPM) castings and reduce wall thickness, improve tolerances and make them more economical. Rheocasting can enable die casters to enter this new market of structural castings including Gigacastings, produce parts previously thought impossible to cast (and on much smaller machines than thought), and expand the growing structural die casting market even faster and further.

Abstract: Semisolid castings are usually produced using primary Al alloys to ensure significant mechanical performances. However, the need to increase the use of secondary alloys is becoming more and more urgent to reduce the carbon footprint of the manufacturing process. In fact, it is well known that the production of primary alloys is far more demanding in terms of energy and emissions than the recycling route. To extend the use of secondary alloys to semisolid processing, it is necessary to thoroughly understand their properties and how they can influence a material with peculiar properties as the semisolid one. Besides microstructural and mechanical features, the rheological behaviour also plays a major role when dealing with processing metals in the semisolid state. Therefore, in the present study, a rheological characterization of secondary AlSi7Mg commercial alloy was carried out and compared to that of the conventional primary alloy. In details, a different content of Fe, Cu and Mn was considered, as these impurities easily form primary intermetallic particles, which can remain dispersed in the liquid matrix of the semisolid metal. The aim of this work is to understand if this can affect the rheological properties of the considered semisolid alloy. Flow curves and yield stresses were obtained from the experimental results to compare the behaviour of the different alloys.