Making sustainable aluminum by recycling scrap: The science of “dirty” alloys

Aluminum recycling currently occurs in a cascading fashion, where some alloys, used in a limited number of applications, absorb most of the end-of-life scrap. An expected increase in scrap supply in coming decades necessitates restructuring of the aluminum cycle to open up new recycling paths for alloys and avoid a potential scrap surplus. This paper explores various interventions in end-of-life management and recycling of automotive aluminum, using a dynamic substance flow analysis model of aluminum and its alloying elements with resolution on component and alloy level (vehicle-component-alloy-element model). It was found that increased component dismantling before vehicle shredding can be an effective, so far underestimated, intervention in the medium term, especially if combined with development of safety-relevant components such as wheels from secondary material. In the long term, automatic alloy sorting technologies are most likely required, but could at the same time reduce the need for magnesium re...

Long-Term Strategies for Increased Recycling of Automotive Aluminum and Its Alloying Elements

The cooling rate-dependent modification effect of Mn on the formation of Fe-containing intermetallic phases during solidification of Al-Si-Mg secondary cast aluminum alloys [containing 0.5 to 1 pct Fe (All compositions are in wt pct unless otherwise stated.)] was investigated by CALculation of PHAse Diagrams (CALPHAD) modeling and solidification experiments. The critical Mn concentration required to prevent the formation of detrimental β-Al5FeSi was found to be dependent on both the alloy composition (particularly the Fe/Mn ratio) and the cooling rate. A map of Fe/Mn ratio vs cooling rate was created, to summarize the metallurgical conditions of Fe-rich intermetallic phase formation. By understanding such formation conditions, the microstructure of aluminum castings can be controlled to create low-cost secondary alloys with high Fe content.

A Formation Map of Iron-Containing Intermetallic Phases in Recycled Cast Aluminum Alloys

Study of the evolution mechanisms of Fe-rich phases in Al-Si-Fe alloys with Mn modification using synchrotron X-ray imaging

While research on lightweight materials has been carried out for decades, it has become intensified with recent climate action initiatives leading pathways to net zero. Aluminum alloys are at the pinnacle of the light metal world, especially in the automotive and aerospace industries. This review intends to highlight recent developments in the processing, structure, and mechanical properties of structural Al-Si alloys to solve various pressing environmental issues via lightweighting strategies. With the excellent castability of Al-Si alloys, advancements in emerging casting methods and additive manufacturing processes have been summarized in relation to varying chemical compositions. Improvements in thermal stability and electrical conductivity, along with superior mechanical strength and fatigue resistance, are analyzed for advanced Al-Si alloys with the addition of other alloying elements. The role of Si morphology modification, along with particle distribution, size, and precipitation sequencing, is discussed in connection with the improvement of static and dynamic mechanical properties of the alloys. The physics-based damage mechanisms of fatigue failure under high-cycle and low-cycle fatigue loading are further elaborated for Al-Si alloys. The defect, porosity, and surface topography related to manufacturing processes and chemical compositions are also reviewed. Based on the gaps identified here, future research directions are suggested, including the usage of computational modeling of microstructures and the integration of artificial intelligence to produce mass-efficient and cost-effective solutions for the manufacturing of Al-Si alloys.

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A Review on Processing–Microstructure–Property Relationships of Al-Si Alloys: Recent Advances in Deformation Behavior

Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy’s ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed α-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure–property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the α-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

After studying CO2 emissions caused by vehicles itself, automotive manufacturers now also consider CO2 emission during the production of vehicles and attempt to reduce them according to a holistic approach. This is where AUDI AG as first OEM together with AMAG Casting applies this approach at the production of structural components, which have been produced by primary alloys up to now. This component segment, which is significantly growing by now, requests mainly high ductility values, in order to absorb as much energy as possible in the case of a crash. In addition to the Fe-content, recycling alloys also have further tramp elements, which occur inevitably at scrap treatment. Besides Cu and Zn there are also elements like Bi, Cr, Ni, Sb, Sn etc. which have to be considered, since they influence the requested alloy properties in a negative way. The results of the existing work show that skilled scrap input at the alloy production can reduce this negative effect close to zero.

Using Scrap in Recycling Alloys for Structural Applications in The Automotive Industry

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Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

Using Scrap in Recycling Alloys for Structural Applications in The Automotive Industry