Aluminum Alloys and Their Properties

Main Aluminum Alloys: they are divided into two main groups according to how they are manufactured.

Wrought aluminum alloys
Cast aluminum alloys.

The alloying elements added to aluminum increase its strength properties; strength in particular increases. The main alloying elements consist of magnesium, manganese, silicon, copper, zinc, and sometimes lead, nickel, and titanium.

Wrought Aluminum Alloys and Their Properties

These alloys are examined in two groups: naturally hard alloys and heat-treatment hardenable alloys.

Heat-Treatment Hardenable Aluminum Alloys and Their Properties

Mg-Si-Al: Contains 0.3–1.5% Mg, 0.2–1.5% Si, and 1.5% manganese in its composition. It also contains 0.1% copper, 0.5% iron, and 0.05% zinc. Its specific gravity is 2.7 kg/dm³; it has good formability and polishing capability, medium strength, and is resistant to corrosion.

Cu-Mn-Al: Contains 2.5%–5% Cu, 0.2%–2.5% Mg, 0.3%–1.5% Mn, and
0.2%–1.5% Si. It also contains 0.5% iron and 0.1% zinc; its specific gravity is 2.3. It hardens at room temperature as a result of heat treatment. It has a high tensile strength. In the hardened state, its strength reaches that of St. 52 steel.

Cu-Ni-Al: Contains 3.5–4.5% Cu, 1.8–2.2% nickel, 1–1.8% magnesium, and also 0.5% Si, 0.5% iron, and 0.1% zinc. It hardens at room temperature as a result of heat treatment. It does not lose its strength when hot.

Cu-Al: Contains 4.5–6% Cu, 0.4–0.6% manganese, and 0.2–0.5% Si in its composition; its specific gravity is 2.8. Since it has good strength, it’s used for producing highly stressed parts. This alloy is also called Lautal Qualitaet 55 Allautal.

Properties of aluminum-copper alloys:

• High strength (2119: σTS 505 MPa).
• Good creep resistance at high temperature.
• High toughness at cryogenic temperature.
• Good machinability.

Zn-Mg-Al: Has a higher strength than all other aluminum alloys. Specific gravity: 2.8.

Basis of Heat Treatment:

If a cold-deformed material is annealed, it regains its own normal hardness and strength. It loses the hardness and strength gained from cold deformation. The grains return to their normal shape again. (This is the recrystallization phenomenon.)

There is the following difference between aluminum and aluminum alloys that harden as a result of heat treatment: after aluminum is annealed, it loses some of its strength and hardens only as a result of cold deformation.

Hardenable aluminum alloys, on the other hand, can have their strength and hardness increased by annealing up to a certain temperature, quenching, and then holding at a certain temperature for a certain time. This holding period is called aging, and the phenomenon is called precipitation hardening.

Material that hardens this way is called precipitation-hardening alloys. Aging is sometimes also carried out at room temperature; the first case is called artificial aging, and the second natural aging. In some books, the first form is called hot aging and the second is called cold aging.

Naturally Hard Aluminum Alloys and Their Properties

Mg-Al: Contains 2.5–1.2% magnesium and 0.0% manganese in its composition. Its specific gravity is 2.6–2.7. It’s resistant to seawater and has very high strength. It is resistant to corrosion.

Mg-Mn-Al Contains 2–2.5% Mg, 1–2% Mn, 0–0.2% Sb, and also 0.8% Fe+Si, 0.05% Cu, and 0.05% Zn. Its specific gravity is 2.7. It’s resistant to seawater. This alloy is also sold on the market under the trade names Ks-Seewasser, Peraluman, Duralumin Mg 25.

Si-Al: Contains 12%–13.5% silicon. Its specific gravity is 2.7. Its strength is higher than pure aluminum and it’s resistant to corrosion. This alloy is also called SILUMIN.

Formability of Wrought Alloys

Wrought aluminum alloys can be easily formed through processes like rolling and extrusion.

Complex Shapes of Cast Alloys

Cast aluminum alloys, poured into a mold in liquid form, make it possible to produce parts with complex geometries.

Series Number Classification

Aluminum alloys are classified with a standard 4-digit series number according to their main alloying element.

Cast Aluminum Alloys and Their Properties

Cu-Al: Contains 7–9% copper in its composition. It’s shaped by sand casting and permanent-mold (chill) casting. Specific gravity: 2.85–2.9. It has good castability. A strength of 12–18 kg/mm² is obtained in sand casting and 12–20 kg/mm² in permanent-mold casting.

Zn-Cu-Al: Contains 8–12% zinc and 2–5% copper in its composition, and has good castability. Specific gravity: 2.9–2.95. Its strength is higher than pure aluminum. A strength of 12–18 kg/mm² is obtained in sand casting and 12–20 kg/mm² in permanent-mold casting.

Cu-Ni-Al: Contains 3.8–4.2% copper, 1.7–2% nickel, and 1.2–1.7% magnesium in its composition. It hardens as a result of heat treatment. Its strength is 18–20 kg/mm² in sand casting and 19–21 kg/mm² in permanent-mold casting. After heat treatment, the achieved strength rises to 24–27 kg/mm² in sand-cast parts and 27–34 kg/mm² in permanent-mold cast parts. Its specific gravity is 2.75.

Si-Al: This alloy contains 11–13.5% silicon. Its specific gravity is 2.65. It has excellent casting properties. This alloy is also called silumin. Among aluminum alloys, this one has the lowest melting temperature (575°C). It has a strength of 17–22 kg/mm² in sand-cast parts and 18–26 kg/mm² in permanent-mold cast parts.

Si-Cu-Al: This alloy contains 11–13.5% silicon, 0.7–0.9% copper, and 0.2–0.4% manganese in its composition. Its specific gravity is 2.65. It has quite good casting properties. This alloy is also called copper-silicon alloy; its strength is 17–22 kg/mm² in sand casting and 18–22 kg/mm² in permanent-mold casting.

Si-Mn-Al: This alloy contains 11–13.5% silicon, 0.4–0.6% magnesium, and 0.3–0.5% manganese. Its specific gravity, suitable for casting conditions, is 2.65. It can be hardened as a result of heat treatment. The strength of hardened alloys is 25–29 kg/mm² in sand-cast parts and 26–32 kg/mm² in permanent-mold cast parts. This alloy is also called “Silumin gamma.”

Mg-Al: Contains 4–12% magnesium, 0.1% manganese, 0.1–1.5% silicon, and 0–1% lead in its composition. Its specific gravity is 2.6–2.7. It’s resistant to seawater. A strength of 22–26 kg/mm² is obtained in permanent-mold cast parts and 10–16 kg/mm² in sand-cast parts. The most widely used of these alloys are Al Mg 3, Al Mg 5, and Al Mg 7. Al Mg alloys are also sold under the names Ks-Seewasser, Gusspantal, Hydronalium, Bs-Seewasser, Duronolgess, and Gussperaluman.

aluminum alloys al-mg aluminum magnesium

AlMg3 Alloy: Contains 1.8–3.5% magnesium, 0.3–1.3% manganese, and 0–1.3% silicon in its composition. Its specific gravity is 2.7. It’s more resistant to seawater, chemicals, and mild alkaline solutions than aluminum and other alloys. It has good polishing capability. Depending on the amount of silicon it contains, it can be heat-treatment hardened to varying degrees.

Al Mg 5 Alloy: Contains 4.5–5.5% magnesium, 0.1–0.5% manganese, and 0.6–1.5% silicon in its composition. Its specific gravity is 2.6. This alloy’s properties are the same as the Al Mg 3 alloy’s. It has quite good casting properties.

AlMg 7 Alloy: Contains 6%–7.5% magnesium, 0.1–0.5% manganese, and 0.6–1.5% silicon in its composition. Its specific gravity is 2.6. This is also an alloy with quite good casting properties. It has a high resistance limit against chemicals and seawater.

Mg-Mn-Al: Its composition consists of 2%–4% magnesium, 1.2%–1.5% manganese, and 0%–0.2% lead. Its specific gravity is 2.7. It’s 14–18 kg/mm² in sand-cast parts and 15–19 kg/mm² in permanent-mold cast parts. It’s resistant to seawater.

Mg-Si-Al: This is an alloy containing 2.5%–5% silicon, 0.3%–2% magnesium, and 0%–1% manganese. Its specific gravity is 2.7, and it’s a heat-treatment hardenable structure. It has good castability; after being hardened by heat treatment, strength rises to 17–28 kg/mm² in sand-cast parts and to 20–30 kg/mm² in permanent-mold cast parts.