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Aluminum based bearing materials

Dr. Dmitri Kopeliovich

Aluminum based Engine bearing materials provide a good combination of a moderate fatigue strength (load capacity) with a moderate level of anti-friction properties (compatibility, conformability, embedability).
Most aluminum based bearing materials have bi-metal structure. The manufacturing technology of aluminum based bearing materials includes continuous casting followed by bonding the alloy with a steel strip.

Aluminum base bearing materials are:

Bi-metal AlSnSiCu bearing.png  Bi-metal AlSnCu bearing.png

Composition of aluminum based bearing alloys

  • Tin (Sn). Aluminum based bearing alloys commonly contain tin (6-40%) as a soft component. Tin is distributed in aluminum matrix as a separate phase in form of a reticular (network) structure along the edges of aluminum grains.

Tin imparts to the material anti-friction properties (compatibility, conformability, embedability).

  • Silicon (Si). Some of aluminum based bearing alloys contain silicon. Silicon has very high hardness and its inclusions distributed over the aluminum matrix serve as an abrasive particles polishing the mating journal surface.

The abrasive effect of aluminum based bearing alloys containing silicon is particularly important for the crankshafts made of nodular (ductile) cast irons consisting of spheroid nodular Graphite particles within the ferrite matrix. Grinding of the shaft surface causes formation of burred caps of ferrite surrounding the graphite nodules. These sharp edges scratch the bearing surface and decrease its seizure resistance. During the engine operation microscopic silicon particles included in the aluminum matrix remove the ragged edges from the shaft surface. Silicon also hardens the aluminum alloy and increases its fatigue strength.

Most aluminum based alloys are solid solution hardened – strengthening by dissolving an alloying element. However some of the alloys may be dispersion hardened (heat treatable alloys) – strengthening by addition of second phase into metal matrix (Al2Cu, Mg2Si).
Aluminum based bearing alloys are manufactured by continuous casting technology.

In contrast to the copper based bearing alloys, anti-friction properties of which are poor aluminum based tin containing alloys may be used without soft anti-friction overlays.

Most aluminum based engine bearings have bi-metal structure consisting of two layers: a steel back and an aluminum-tin alloy of about 0.01” (0.25 mm) thick.
Load carrying capacity of bi-metal Al20Sn1Cu bearing is 5800 psi (40 MPa).
Load carrying capacity of bi-metal aluminum-tin-silicon-copper bearing is 7250-8700psi (50-60 MPa).

The bearing materials not containing tin or containing low content of tin (less than 6%) are overplated with a thin soft overlay (tri-metal structure and multi-layer structures). The overlay parameters are similar to those used for tri-metal copper based bearings.
Load carrying capacity of tri-metal (overplated) aluminum based bearings is determined by the fatigue strength of the overlays:

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Characteristics of some aluminum based engine bearing materials

Composition Structure Hardness, HV Overlay Applications
Al20Sn1Cu Bi-metal 35 no Low loaded bearings
Al40Sn1Cu Bi-metal 30 no Low loaded bearings, excellent seizure resistance
Al8Sn2Pb2.5Si0.8Cu0.2Cr Bi-metal, no bonding layer 40 no Low and medium loaded bearings, good seizure resistance
Al12Sn4Si1Cu Bi-metal 45 no Low and medium loaded bearings, good seizure resistance, lead free
Al4Si0.5Cu0.5Mg Tri-metal 70 (precipitation hardened) Pb10Sn3Cu Low and medium loaded bearings, good seizure resistance, lead free
Al6.5Sn1Cu0.5Ni Tri-metal 40 Pb18Sn2Cu with nickel barrier Highly loaded bearings
Al6.5Sn1Cu0.5Ni Tri-metal 40 MoS2 in resin Racing car engine bearings
Al6.5Sn1Cu0.5Ni Solid 40 no Thrust washers
Al11Si11Mg1Cu1Ni Solid 100 (precipitation hardened) Pb18Sn2Cu with nickel barrier Small end bushes
Al4.5Zn1Pb1Cu0.5Mg Tri-metal 55 Al20Sn (sputter) with nickel barrier Highly loaded conrod bearings

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aluminum_based_bearing_materials.txt · Last modified: 2018/02/03 by dmitri_kopeliovich
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