Aluminium metallography

Unalloyed aluminum: light microscopy


Iron and silicon are constant and unavoidable impurities in virtually all aluminum alloys. Since the solubility of iron in solid aluminum is very low, the phase types of aluminum-iron and aluminum-iron-silicon are present in the microstructure of all brands technical aluminum, except for the special treated ultrapure aluminum.

Iron phase in aluminum

The cast aluminum these phases - equilibrium – can be phase FeAl3, Fe3unlucky12 or Fe2Si2Al9. Moreover, during rapid cooling can form some metastable nonequilibrium phase, for example, FeAl6.

Impurities and additives, such as copper and magnesium, if they are in the amount of, insufficient to form eigenphases, promote the formation of unstable phases types. To find them use a high resolution microscope and sophisticated techniques. Subsequent thermal treatment usually facilitate the transition from the unstable to the stable phases of type.

Aluminum microstructure 1100

The figure 1 shows a typical aluminum casting structure 1100.

Figure 2 shows the influence of aluminum homogenizing annealing 1100 before deformation processing.

The figure 3 shows the typical deformed microstructure.

Grain structure of annealed aluminum sheet (Figure 4) demonstrates a slight deviation from the equiaxed structure due to elongated iron-containing particles. The apparent volume distribution of second phases particles is a direct function of the iron content.

figure-1Figure 1 - Aluminum Ingot 1100 as-cast shows the typical microstructure of components, preferably Fe3unlucky12, which are located in the interdendritic interstices. (0.5% 0-solution of hydrofluoric acid, 455x) [1]

figure-2Figure 2 - The homogenized ingot of aluminum 1100. Under the influence of heating of the particles vyskotemperaturnogo Fe3unlucky12 (light) turned into FeAl particles3 (dark). (20% sulfuric acid solution, 455x) [1]

figure-3Figure 3 - Fragmentation and redistribution structure as a result of the deformation processing. (0.5% hydrofluoric acid solution, 455x) [1]

figure-4Figure 4 - aluminum sheet 1100: slightly elongated grain structure. (Electrolytic etching, 90x) [1]


1. Aluminum: Properties and Physical Metallurgy – ed. John E. Hatch – ASM International – 1984