As known, wrought aluminum alloys are divided into eight major series alloys by their main alloying elements. Therefore, each such Series will have its own characteristics of the microstructure. Another division of aluminum alloys relates to their ability to heat treatment (series 2xxx, 6xxx, 7xxx) or strain hardening - cold working (1xxx, 3xxx, 5xxx). It is also reflected in the microstructure of the alloys.
The microstructure of the technical 1xxx series aluminum
The microstructure of this series are usually phase aluminum-iron and aluminum-iron-silicon. This is due to the fact, iron and silicon that have low solubility in aluminum and are impurity elements. Therefore, in this metal by etching 0,5 %-a saline solution of hydrofluoric acid easily detected phase such as FeAl3, Fe3SiAl or Fe2Si2Al9. If the interest is the grain structure of aluminum, the anodising is used with the Barker reagent.
The microstructure of aluminum alloys 3xxx series
These alloys have a major alloying element manganese. They therefore contain such phases, как (Mn, Fe) Al6 или (Mn, Fe)3unlucky12, which are identified by etching in 10 %-SG phosphoric acid solution H3PO4. To reveal the grain structure, obtained by cold working or annealing, used anodizing.
The microstructure of aluminum alloys 4xxx series
Most of these alloys have high silicon content and are used as materials for soldering and welding, when they are melted. Casting phases are typically silicon particles Sii Fe2Si2Al9. When heat-treated silicon koalestsioniruet, whereas the iron-containing phases remain unchanged. These particles are etched 0,5 %-a saline solution of hydrofluoric acid.
The microstructure of aluminum alloys series 5xxx
Magnesium – the main element in these alloys. It has a significant solubility in aluminum;. When excess Content may be present in the form of eutectic particles of Mg2Al3. After cold rolling and annealing them can be found at the grain boundaries, and cold working, they can be allocated as a strain bands. In both cases, the structure is revealed by etching in 10 %-hydrochloric phosphoric acid H3PO4. Since this series of alloys chromium is a common additive, the compound of Cr2Mg3Al18 It may appear in the form of fine dispersoids.
The microstructure of aluminum alloys 6xxx series
This family of alloys is thermally hardened by precipitation particles Mg2Si. Etching of microstructures produced 0,5 %-a saline solution of hydrofluoric acid. Etching identifies insoluble iron type phase Fe3unlucky12 и Fe2Si2Al9, and coarse separation Mg2Si. An initial separation stage can only be seen through an electron microscope.
The microstructure of aluminum alloys, 2xxx series
The fully microstructure of these alloys can only be seen through an electron microscope. They have a very complex structure because of the large amounts of additives, which are used to increase strength, corrosion resistance or control grain size. Therefore the microstructure of these alloys multiphase, especially in the state of the cast. Etching of thin lead in 10 %-SG phosphoric acid solution. Typical phase - Al2CuMg и Al7Cu2Fe. When the content of copper 3,5-5 % they can be seen in the light microscope by etching reagent Keller.
The microstructure of the 7xxx series aluminum alloys
This series of aluminum alloys containing zinc, magnesium and copper as main alloying elements, and chromium additives, zirconium, manganese, as well as iron and silicon. Therefore, the number of components and phases in the microstructure is quite large. For identification of used reagent Keller. Etched grain structure 10 %-a saline solution of phosphoric acid.
A source: TALAT 1202