Aluminium–magnesium–silicon alloys

Aluminium–magnesium–silicon alloys are aluminium alloys—alloys that are mainly made of aluminium—that contain both magnesium and silicon as the most important alloying elements in terms of quantity. Both together account for less than 2 percent by mass. The content of magnesium is greater than that of silicon, otherwise they belong to the aluminum–silicon–magnesium alloys.
AlMgSi is one of the hardenable aluminum alloys, i.e. those that can become firmer and harder through heat treatment. This curing is largely based on the excretion of magnesium silicide. The AlMgSi alloys are therefore understood in the standards as a separate group and not as a subgroup of aluminum-magnesium alloys that cannot be hardenable.
AlMgSi is one of the aluminum alloys with medium to high strength, high fracture resistance, good welding suitability, corrosion resistance and formability. They can be processed excellently by extrusion and are therefore particularly often processed into construction profiles by this process. They are usually heated to facilitate processing; as a side effect, they can be quenched immediately afterwards, which eliminates a separate subsequent heat treatment.

Alloy constitution

Phases and balances

The AlMg₂Si system forms a Eutectic at 13.9% Mg₂Si and 594 °C. The maximum solubility is 583.5 °C and 1.9% Mg₂Si, which is why the sum of both elements in the common alloys is below this value. The stoichiometric composition of magnesium to silicon of 2:1 corresponds to a mass ratio of 1.73:1. The solubility decreases very quickly with falling temperature and is only 0.08 percent by mass at 200 °C. Alloys without further alloying elements or impurities are then present in two phases with the-mixed crystal and thephase. The latter has a melting point of 1085 °C and is therefore thermally stable. Even clusters of magnesium and silicon atoms that are only metastable dissolve only slowly, due to the high binding energy of the two elements.
Many standardised alloys have a silicon surplus. It has little influence on the solubility of magnesium silicide, increases the strength of the material more than an Mg excess or an increase in the Mg₂Si content, increases the volume and the number of excretions and accelerates excretion during cold and hot curing. It also binds unwanted impurities; especially iron. A magnesium surplus, on the other hand, reduces the solubility of magnesium silicide.

Alloying elements

In addition to magnesium and silicon, other elements are contained in the standardized varieties.

Copper is used to improve strength and hot curing in quantities of 0.2-1%. It forms the Q phase. Copper leads to a denser dispersion of needle-shaped, semi-coherent excretion. In addition, there is the phase before the for the aluminium–copper alloys are typical. Alloys with higher copper content are mainly used in aviation.
Iron occurs in all aluminium alloys as an impurity in quantities of 0.05-0.5%. It forms the phases Al₈Fe₂Si, Al₅FeSi and Al₈FeMg₃Si₆, which are all thermally stable, but undesirable because they brittle the material. Silicon surpluses are also used to bind iron.
Manganese and chromium is deliberately added. If both are allocated at the same time, the sum of the two elements is less than 0.5%. After annealing, they form a dispersion of excretions at at least 400 °C and thus improve strength. Chromium is mainly effective in combination with iron.
As dispersion formers are coming zirconium and vanadium for use.
Dispersions

have little influence on strength. If magnesium or silicon excrete on them during cooling after the solution annealing and, thus, do not form magnesium silicide as desired, they even lower the strength. They increase the sensitivity to deterrent. However, if the cooling speed is insufficient, they also bind excess silicon, which would otherwise form coarser excretions and thus reduce strength. The dispersion particles activate further even when cured. Sliding planes, so that theDuctility increases and, above all, intergranular fracture can be prevented. The alloys with higher strength therefore contain manganese and chromium and are more sensitive to deterrents.
The following applies to the effect of the alloying elements with regard to dispersion formation:

The strength at room temperature hardly changes. However, the flow limit at higher temperatures rises sharply, which makes theReformability is limited and above all unfavourable in the extrusion is because it increases the minimum wall thickness.
The recrystallisation is made more difficult, which prevents coarse grain formation and has a positive effect on formability.
Dislocation movements are blocked at low temperatures, which improved fracture toughness.
Dispersions of AlMn bind oversaturated silicon during cooling after solution annealing. This improves crystallization and avoids excretion-free zones that otherwise arise at the grain boundaries. This improves the fracture behaviour from brittle to ductile and intragranular.
The sensitivity to quenching increases because precipitated silicon is required for hardening. Alloys containing Mn or Cr must therefore be cooled faster than those without these elements.
6000 series

6000 series are alloyed with magnesium and silicon. They are easy to machine, are weldable, and can be precipitation hardened, but not to the high strengths that 2000 and 7000 can reach. 6061 alloy is one of the most commonly used general-purpose aluminium alloys.

Alloy	Al contents	Alloying elements	Uses and refs
6005	98.7	Si 0.8; Mg 0.5	Extrusions, angles
6005A	96.5	Si 0.6; Mg 0.5; Cu 0.3; Cr 0.3; Fe 0.35
6009	97.7	Si 0.8; Mg 0.6; Mn 0.5; Cu 0.35	Sheet
6010	97.3	Si 1.0; Mg 0.7; Mn 0.5; Cu 0.35	Sheet
6013	97.05	Si 0.8; Mg 1.0; Mn 0.35; Cu 0.8	Plate, aerospace, smartphone cases
6022	97.9	Si 1.1; Mg 0.6; Mn 0.05; Cu 0.05; Fe 0.3	Sheet, automotive
6060	98.9	Si 0.4; Mg 0.5; Fe 0.2	Heat-treatable
6061	97.9	Si 0.6; Mg 1.0; Cu 0.25; Cr 0.2	Universal, structural, aerospace
6063 & 646g	98.9	Si 0.4; Mg 0.7	Universal, marine, decorative
6063A	98.7	Si 0.4; Mg 0.7; Fe 0.2	Heat-treatable
6065	97.1	Si 0.6; Mg 1.0; Cu 0.25; Bi 1.0	Heat-treatable
6066	95.7	Si 1.4; Mg 1.1; Mn 0.8; Cu 1.0	Universal
6070	96.8	Si 1.4; Mg 0.8; Mn 0.7; Cu 0.28	Extrusions
6081	98.1	Si 0.9; Mg 0.8; Mn 0.2	Heat-treatable
6082	97.5	Si 1.0; Mg 0.85; Mn 0.65	Heat-treatable
6101	98.9	Si 0.5; Mg 0.6	Extrusions
6105	98.6	Si 0.8; Mg 0.65	Heat-treatable
6113	96.8	Si 0.8; Mg 1.0; Mn 0.35; Cu 0.8; O 0.2	Aerospace
6151	98.2	Si 0.9; Mg 0.6; Cr 0.25	Forgings
6162	98.6	Si 0.55; Mg 0.9	Heat-treatable
6201	98.5	Si 0.7; Mg 0.8	Rod
6205	98.4	Si 0.8; Mg 0.5;Mn 0.1; Cr 0.1; Zr 0.1	Extrusions
6262	96.8	Si 0.6; Mg 1.0; Cu 0.25; Cr 0.1; Bi 0.6; Pb 0.6	Universal
6351	97.8	Si 1.0; Mg 0.6;Mn 0.6	Extrusions
6463	98.9	Si 0.4; Mg 0.7	Extrusions
6951	97.2	Si 0.5; Fe 0.8; Cu 0.3; Mg 0.7; Mn 0.1; Zn 0.2	Heat-treatable

Grain boundaries

to the grain boundaries prefer silicon to be excreted, as it has germination problems. In addition, magnesium silicide is excreted there. The processes are probably similar to those of the AlMg alloys, but still relatively unexplored for AlMgSi until 2008. The phases excreted at the grain boundaries lead to the tendency of AlMgSi to brittle grain boundary breakage.

Compositions of standardised varieties

All information in mass percent. EN stands for European standard, AW for aluminium wrought alloy; the number has no other meaning.

Numerically	Chemical	Silicon	Iron	Copper	Manganese	Magnesium	Chrome	Zinc	titanium	other	Other	Other	Aluminum
EN AW-6005	AlSiMg	0.6–0.9	0.35	0.10	0.10	0.40–0.6	0.10	-	-	-	0.05	0.15	Rest
EN AW-6005A	AlSiMg	0.50–0.9	0.35	0.3	0.50	0.40–0.7	0.30	0.20	0.10	0.12–0.5 Mn+Cr	0.05	0.15	Rest
EN AW-6008	AlSiMgV	0.50–0.9	0.35	0.30	0.30	0.40–0.7	0.30	0.20	0.10	0.05–0.20 V	0.05	0.15	Rest
EN AW-6013		0.6-1.0	0.5	0.6-1.1	0.20 - 0.8	0.8-1.2	0.10	0.25	0.10	-	0.05	0.15	Rest
EN AW-6056		0.7-1.3	0.50	0.50-1.1	0.40 - 1.0	0.6-1.2	0.25	0.10–0.7	-	0.20 Ti+Zr	0.05	0.15	Rest
EN AW-6060	AlMgSi	0.30–0.6	0.10 - 0.30	0.10	0.10	0.35–0.6	0.05	0.15	0.10	-	0.05	0.15	Rest
EN AW-6061		0.40–0.8	0.7	0.15–0.40	0.15	0.8-1.2	0.04 - 0.35	0.25	0.15	-	0.05	0.15	Rest
EN AW-6106	AlMgSiMn	0.30–0.6	0.35	0.25	0.05–0.20	0.40 - 0.8	0.20	0.10	-	-	0.05	0.15	Rest