Iron in the foundry aluminum alloys

The main factors influencing iron

1. Iron is the main impurity, which is responsible for the low level of toughness of conventional aluminum alloys.
2. iron-containing phase, which is formed from a liquid in high-silicon aluminum alloys is β-FeSiAl₅.
3. Β-FeSiAl particles are commonly referred to as needle-shaped or needle-shaped, although in fact they are plates.
4. Additives in manganese alloy in quantity, equal to half the iron content, меняют фазу β-FeSiAl на фазу α-FeSiAl с химической формулой (Fe,Mn)₃Si₂Al₁₅. This phase is no longer needle-shaped, but something resembles a written font. She is not so harmful, like a needle, хотя еще остается охрупчивающей фазой (рисунок 2).

Figure 1 - β-FeSiAl needles

Figure 2 - Particles α-FeSiAl - less harmful, than β-FeSiAl needles. Raft A357

Cooling rate and size of β-FeSiAl needles

1. 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.
2. С увеличением содержания железа в сплаве длина игл β-FeSiAl также увеличивается (рисунок 3).

Figure 3 – Зависимость длины игл β-FeSiAl от междендритного расстояния вторичных дендридов (Источник – Biswal и др.)

Β-FeSiAl needles and mechanical properties

1. The presence of β-FeSiAl needles in the microstructure of aluminum alloys of aluminum reduces their mechanical properties.
2. Most β-FeSiAl needles reduce the viscous properties of aluminum alloys, особенно вязкость вторичных сплавов с высоким содержанием железа (рисунок 4).

Figure 4 – Сравнение механических свойств сплава А357 с высоким (0,093 %) и низким (0,055 %) содержанием железа (Источник: F. Major, Alcan)

A source: European Aluminium Association, 2002