“Dirty” wrought alloys: Tolerance of Al-Mg-Si extrusion alloys for high Fe contents and the role of effective Si

Description

Generally, high Fe levels are undesired in Al-Mg-Si wrought alloys because Fe forms brittle intermetallic phases with Al and Si. These AlFeSi-type intermetallics are known fracture initiation sites, hence thought to reduce ductility and formability, and can lead to inferior surface finish. Unfortunately, aluminum scrap is often contaminated with steel parts. Since Fe is difficult to remove metallurgically from Al melts, dilution with large quantities of high-purity primary Al is the standard procedure to meet the rather low maximum permissible Fe levels imposed by standards.

Recycling of Al requires only 5–10 % of the energy needed for primary production. In light of the climate crisis, improving the sustainability of Al products by increasing their recycled contents is of great importance. In particular, it is desirable to avoid down-cycling of wrought alloys into cast alloys. To achieve these goals, the development of wrought alloys with increased tolerance for tramp elements, most importantly Fe, is key.

In this study, we study Al-Mg-Si wrought alloys, based on common extrusion alloys (6060, 6005A, 6082), with high, non-standard Fe contents (i.e., 0.7 wt. %). We report the microstructure and mechanical properties of the alloys after extrusion and artificial ageing and compare them to the standard alloys. We found that 6082 is more tolerant to above-standard Fe contents than 6005A, which in turn is more tolerant than 6060: The strength of 6082+Fe content is comparable to that of standard 6082, while the artificial ageing potential of 6060+Fe is drastically reduced compared to 6060. Our data and values gathered from literature show that the effective Si content is a good overall predictor of alloy strength. Effective Si is not bound in AlFeSi-type phases and available for precipitation hardening. However, additional mechanisms are at play and further research is necessary to leverage the full potential of wrought alloys with high Fe contents.

Period	21 Jun 2023
Event title	LightMAT: 5th International Conference on Light Materials - Science and Technology
Event type	Conference
Location	Trondheim, NorwayShow on map
Degree of Recognition	International