An innovative secondary aluminium AlSi10MnMg(Fe) for structural components with high ductility requirements

AlSi10MnMg primary aluminum alloy is widely used to manufacture structural components in the automotive market, such as front crash towers, door frames and rear side members. Aluminum structural components manufactured by vacuum high pressure casting (V-HPDC) are produced from this alloy. The main differences between components manufactured using conventional high pressure casting (HPDC) technology and vacuum technology are ductility or energy absorption capacity. Taking as reference the UNE-EN-1706:2020 standard, the minimum elongation required for the AlSi9Cu3(Fe)(Zn) alloy (the secondary alloy most used in the conventional HPDC process) is 1% in state F (as-cast ), while for a V-HPDC component cast in AlSi10MnMg a minimum elongation of 12% is required after T7 heat treatment. This enormous difference is associated with the different compositions and microstructures of both alloys, with greater cleanliness of the casting and lower porosity and defects.

The primary alloy AlSi10MnMg has a low iron content (less than 0.25 wt.%), shows a globular modified Si eutectic along with primary aluminum dendrites. Al12Mn3Si3 intermetallic phases are also observed in the eutectic area with polygonal-globular shapes. Under conditions F (molten state), Mg2Si intermetallic phases are present in the microstructure. These Mg2Si phases are finely dissolved and precipitated in the aluminum matrix after applying T6 or T7 heat treatments consisting of solution treatment, rapid cooling and artificial aging treatment.

Innovative secondary aluminum alloys have achieved mechanical properties comparable to those of the corresponding primary alloys, with lower costs, energy savings and lower CO2 emissions compared to the production of primary aluminum alloys. The carbon footprint of secondary aluminum is significantly lower than that of primary aluminum alloys, which is why the automotive industry is very interested in using them to reduce their environmental impact.

The objective of this work is to demonstrate that if an appropriate metallurgical treatment is applied, it is possible to obtain a recycled aluminum alloy AlSi10MnMg(Fe) with equal metal cleanliness and mechanical properties comparable to those of the primary alloy AlSi10MnMg. For this study, the new secondary AlSi10MnMg(Fe) developed in a previous study was selected, with 0.6 wt% Fe and 0.4 wt% Mn, which demonstrated mechanical properties similar to those of a primary AlSi10MnMg alloy.