Aluminium casting alloys

Aluminium-tin casting alloys

Specifically for bearing

  • These tin-alloyed aluminum alloys were developed specifically for bearing applications.
  • For bearing quality, the main criteria are load-bearing capacity, fatigue strength and corrosion resistance under lubrication conditions in internal combustion engines.
  • Tin alloyed aluminum alloy bearings are unrivaled among other types of bearing materials.

Aluminum-tin phase diagram

fazovaya-diagramma-alyuminiy-olovo
Aluminum-tin phase diagram

Aluminum-tin system alloys contain about 6% tin, as well as small amounts of copper and nickel to increase strength. They are used for cast bearings. Very good sliding in these alloys is ensured by tin.

Aluminum-tin alloys

8xx.x series alloys

  • American casting aluminum-tin alloys 850.0, 850.1 and 852.0 can be cast in either sand or die casting.
  • However, alloys 850.0 (6.3Sn-1Cu-1Ni) and 852.0 (6.3Sn-2Cu-1.2Ni-0.8Mg) are usually cast into permanent molds only.
  • Sand casting is used for large rolling mill bearings, which are typically made from alloy 851.0 (6.3Sn-2.5Si-1Cu-0.5Ni).

Bearing structure

The “bearing” properties of aluminum-tin alloys are highly dependent on the casting method. A fine interdendritic distribution of tin is essential for optimal bearing properties. This requires a small interdendritic distance, and this distance can only be achieved with rapid cooling casting methods.

Long solidification interval

From a casting process point of view, the aluminum-tin alloy system is unique. Solidification of the alloy in the casting mold begins at a temperature of about 650 ºC, and tin remains liquid until about 225 ºC. Such a too large solidification temperature range poses difficulties for casting. To avoid excessive macrosegregation, high solidification rates of castings are recommended.

Casting aluminum alloy 850.0

Alloy formula:

6.2Sn-1Cu-1Ni

Chemical composition:

  • copper: 0.7-1.3%;
  • magnesium: 0.10 max;
  • silicon: 0.7% max;
  • iron: 0.7% max.
  • tin: 5.5-7.0%;
  • nickel: 0.7-1.3%;
  • titanium: 0.20% max;
  • others: 0.30% max;
  • aluminum: the rest.

Impact of impurity content:

  • high content of iron, manganese or magnesium reduces ductility and increases hardness;
  • high silicon content improves sliding characteristics.

Typical mechanical properties in T5 condition:

  • tensile strength: 160 MPa;
  • yield strength: 75 MPa;
  • relative elongation: 10%;
  • hardness: 45 HB;
  • Poisson’s ratio: 0.33;
  • modulus of elasticity: 71.0 GPa.

Physical properties:

  • density: 2.880 g/cm3;
  • liquidus temperature: 650 ºС;
  • solidus temperature: 225 ºС.

Technological properties:

  • melting point: from 650 to 730 ºС;
  • casting temperature: from 650 to 705 ºС;
  • aging temperature: 230 ºС, holding time – 8 hours.

Sources:

  1. Aluminum and Aluminum Alloys, ASM International, 1996
  2. Aluminum Alloy Castings: Properties, Processes And Applications – J. Gilbert Kaufman, Elwin L. Rooy