Adding Value to Secondary Aluminum Casting Alloys: A Review on Trends and Achievements

Abstract

Aluminum is a critical element of the circular economy as it can be recycled several times. Moreover, Al recycling is a more economically and environmentally efficient procedure than the primary Al production from ores. Secondary aluminum alloys are mostly used in casting applications since it is possible to accommodate their chemical composition through secondary manufacturing processes. However, the quality of the alloys may be considerably altered during the different steps of the recycling process. Inadequate waste sorting might result in excessive contamination. Iron is the most dangerous contaminant because it causes brittle and fragile intermetallic phases, which significantly impacts the mechanical characteristics of alloys. In addition, the microstructure of the alloy changes significantly after multiple cycles of remelting. These issues lead to the downcycling of aluminum, i.e., in other words, the reduction in the overall quality of the alloys. Thus, it has been shown that a number of procedures, including ultrasonic melt treatment and microalloying with rare earths, can somewhat alter the shape of the Fe-rich phases in order to reduce the shortcomings of downcycling. However, a solid mechanical characterization is still missing in order to improve the Fe-rich phase alteration.

Energy and Environmental Savings by and for Steel Lightweight

“…One of the biggest obstacles is the irregular fluctuations in trace elements in dealing with complex scraped aluminium alloys that are often impossible or extremely challenging to eliminate during the relatively low temperature of remelting. Therefore, secondary aluminium ingots recycled from scrap are mainly low-grade materials [66][67][68] and cannot be used to produce high-purity and high-grade wrought materials 50), and from an economic view, the value of alloy-specific aluminium is 60 % of the primary aluminium 66) .…”

The Influence of Mn Addition on Corrosion Resistance in Secondary Aluminium Alloy AlSi7Mg0.3 after the Heat Treatment

“…The heat-treatable nature of AlSi7Mg0.3 also enables further improvement of its mechanical properties through solution heat treatment and ageing. Despite its advantages, the presence of Fe and other impurities in the recycled aluminium scrap can negatively impact the microstructure and properties of AlSi7Mg0.3 alloys, thus, requiring careful selection of raw materials and precise control of casting conditions [5][6][7][8].…”

Effect of Gating System Design on the Quality of Aluminum Alloy Castings

“…The oxide layer can deteriorate the final quality of the casting if it is entrained into the melt by the turbulence of the melt surface and solidifies in the casting [1][2][3][4][5]. Several studies in recent years indicate that entrained double oxide layers in the casting act as porosity initiators and that hydrogen contributes to pore formation by diffusing between the layers, thereby enlarging the pores [6][7][8].…”