Alloy design for sustainable aluminum high pressure die castings: A review

The use of recycled or scrap or secondary aluminum to manufacture high pressure die castings (HPDC) for structural applications is an opportunity to reduce cost, energy expenditure and emission of greenhouse gases. Technical challenges that must be overcome to achieve this on a large scale include scrap sorting and availability of alloys that can take such feedstock while maintaining desirable performance. This review focuses on structural alloy design with scrap aluminum as feedstock. An overview of HPDC processing and relevant processing-microstructure-property relationships is provided. Common HPDC structural alloy systems in commercial use that accept primary aluminum as feedstock are reviewed. Scrap streams that are relevant for producing HPDC aluminum alloys are discussed. An overview of state-of-the-art tools that can be applied to develop sustainable HPDC alloy compositions is provided. Current sustainable alloy design practices associated with HPDC are summarized and salient metallurgical challenges and opportunities associated with sustainable HPDC alloy design are identified based on our review. It is concluded that design of sustainable compositions of HPDC aluminum alloys for structural applications is now possible, in particular for well-defined scrap such as that coming from automotive wheels. Many opportunities exist to develop new alloy compositions that can effectively utilize current and emerging scrap streams. A grand challenge is the development of new alloys that can incorporate post-consumer mixed scrap as feedstock.