The main factors influencing iron
- Iron is the main impurity, which is responsible for the low level of toughness of conventional aluminum alloys.
- iron-containing phase, which is formed from a liquid in high-silicon aluminum alloys is β-FeSiAl5.
- Β-FeSiAl particles are commonly referred to as needle-shaped or needle-shaped, although in fact they are plates.
- Additives in manganese alloy in quantity, equal to half the iron content, change the β-FeSiAl phase to the α-FeSiAl phase with the chemical formula (Fe, Mn)3Si2Al15. This phase is no longer needle-shaped, but something resembles a written font. She is not so harmful, like a needle, although it still remains an embrittling phase (Figure 2).
Cooling rate and size of β-FeSiAl needles
- Β-FeSiAl needle length is a function of cooling rate. A measure of the cooling rate is the interdendritic distance in the alloy structure.. Higher cooling rate, the smaller the interdendritic distance.
- With an increase in the iron content in the alloy, the length of the β-FeSiAl needles also increases (Fig. 3).
Β-FeSiAl needles and mechanical properties
- The presence of β-FeSiAl needles in the microstructure of aluminum alloys of aluminum reduces their mechanical properties.
- Most β-FeSiAl needles reduce the viscous properties of aluminum alloys, especially the toughness of secondary alloys with a high iron content (figure 4).
A source: European Aluminium Association, 2002