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
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.
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