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:
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:
|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|
|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|