Aluminum alloys for profiles

Sredneprochnye aluminum alloys

6xxx series alloys They are so-called "sredneprochnymi" alloys, which can harden through heat treatment due to excessive precipitates dispersed phase. The main alloying elements are silicon and magnesium, primarily, in an amount of 0,3 to 1,5 %.

These alloys are generally less durable, than alloys of the series 2xxx and 7xxx, but have good formability (for example, at pressing, forging, flexible), good weldability and high corrosion resistance.

This combination of relatively high strength, formability, corrosion resistance of weldability provides these alloys with wide application in the form of profiles in transport engineering (cars, passenger cars), construction (aluminum windows, doors, stairs), in on the sea shore structures and on the high seas, as well as in many other areas.

5 popular aluminum alloys

Although in the world there are more than 70 6xxx series alloys, main types of alloys, included in the European Standard EN 573-3, of which there are only about 30. The remaining alloys are, primarily, variants of base alloys (for such alloys, the second digit in the designation is always zero). Of these thirty alloys most widely used only 6005, 6060, 6063, 6061 and 6082.

Of these five alloys in the world is made more 90 % all pressed aluminum profiles. The share alloys 6005, 6061 and 6082 It constitutes only a fraction of this total. Near 75 % of total profiles made of alloys 6063 or 6060.

GOST 4784-97 and international standards EN and b

The chemical composition of popular alloys 6060, 6063, 6005A, 6061 and 6082, as well as their counterparts according to GOST 4784-97, is shown in Table. The figure shows the contents of magnesium and silicon in the most common alloys. It demonstrates the significant "overlaps" between alloys, especially between 6106 and 6063, differences alloys 6060 and 6063, as well as full match “American” alloy 6063 and "our" alloy AD31.

Alloy 6061 completely coincides with "our" alloy AD33, a raft 6082 – co alloy AD35.

Figure – The content of magnesium and silicon in aluminum alloys 6xxx

Doping of aluminum alloys 6xxx

Properties of the 6xxx series alloys are controlled by their chemical composition as a whole, but the dominant effect of magnesium and silicon. other elements, such as iron, copper, manganese and chromium, also affect the properties of these alloys, but to a lesser extent.

Magnesium and chromium have the greatest impact on the compressibility of the alloy, whereas silicon, iron and manganese have less of an impact on it.

Copper, in quantities, characteristic 6xxx alloys, It has a negligible effect on the compression properties, however, it promotes microfine and homogeneous precipitation of magnesium silicide, Mg₂Si, which has a positive effect on the strength characteristics of the profiles and the reflective properties of anodic oxide coatings.

Solution heat treatment

All alloying elements (except copper) increase the quenching sensitivity of 6xxx alloys, wherein the magnesium has the greatest impact. Manganese and chromium also increases the quench sensitivity, because they are at a temperature homogenization together with aluminum, silicon and iron are involved in the formation of small iron-containing dispersoids. These dispersoids Al-Fe-Mn / Cr-Si act as heterogeneous nucleation centers for isolating magnesium silicide particles in subsequent thermal treatments, which enhances the strength properties of alloys 6xxx.

Effect of alloying on the strength and ductility

All alloying elements improve strength 6xxx alloys, but magnesium, silicon and copper have a maximum effect.

Increased magnesium and silicon adversely affects the plastic and viscous properties of the alloys.

Manganese and chromium have beneficial effects on the viscous properties, whereas copper has hardly any influence on it. The presence of the dispersoid in the alloys, containing manganese / chromium, It promotes the release of magnesium silicide inside the grains and prevents their separation at the grain boundaries and formation of border zones, in which no phase separation of excess. This prevents weakening of the grain boundaries and improves the viscous properties of alloys 6xxx.

Manganese and chromium, Moreover, are used to control recrystallization processes in profiles at the exit from the press: their dispersoids "pierce" the grain boundaries and help in preserving non-crystallized, layered structure, which favorably affects the properties of extruded sections.

Links:
1. aluMATTER
2. COMALCO – TECHNICAL REPORT, 2001