Sustainable Aluminium Alloys

Innovative solutions to shrink a material’s carbon footprint

One aspect key to the sustainable use of recycled aluminium is the development of new, more tolerant alloy concepts. These new concepts make it possible to substantially increase the use of secondary aluminium without significantly compromising functional or safety-related material properties.AlSi7 and AlSi10Mg alloys have become established as the industrial benchmark for cast components in the automotive sector. They are typically used in wheels and load-bearing structural elements (Figure 1). Their excellent castability, mechanical performance and high corrosion resistance satisfy crucial requirements for lightweight construction. The technological challenge (Figure 1) lies in reliably ensuring these properties, even when using heavily mixed recycled aluminium. Based on systematic materials analysis and targeted process development, AMAG has created recycling-optimized variants of AlSi7 and AlSi10Mg. Permitted concentration ranges for tramp elements such as iron (Fe), copper (Cu) and zinc (Zn) have been carefully extended – subject to compliance with requirements regarding strength, elongation, fatigue strength, corrosion resistance and casting behavior. This makes it possible to achieve a significant CO₂ reduction throughout the value chain.Controlling intermetallic phases is at the core of alloy design. Targeted adjustment of the Fe:Mn ratio effectively suppresses the formation of the brittle β-AlFeSi phase. The combination of titanium (Ti) and strontium (Sr) allows both grain refinement and eutectic modification, which makes it possible to maintain high levels of ductility required for safety-critical applications. Depending on the specific application, targeted adjustment of silicon content may be needed to ensure optimal suitability for mechanical joining techniques, such as punch riveting. Reducing the Si content promotes ductility in the joining area and minimizes the risk of failure mechanisms associated with brittle fractures. We also carefully examine the alloy’s electrochemical stability. In copper-bearing Al-Si cast alloys, the ϴ-Al₂Cu phase represents a weakness for corrosion processes. The controlled addition of zinc tends to shift copper into the more thermodynamically stable τ phase, which has a lower electrochemical potential that significantly reduces cathodic attack on the aluminium matrix. In addition, the tolerance thresholds for trace elements have been defined in such a way that potentially critical precipitates are integrated into non-critical phases.The result is an aluminium structural cast alloy based on AlSi10 that is capable of meeting all material engineering requirements set by leading OEMs. It has demonstrated its performance in comprehensive testing, ranging from dynamic stress tests to corrosion load testing to component testing in real-world conditions. Consequently, the new alloy represents a technologically validated and sustainable solution to replace primary aluminium in automotive structural cast components, making it possible to use high levels of recycled aluminium.