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:

• Less expensive than Copper based bearing materials;
• Contain no (or low) hazardous lead;
• Possess good corrosion resistance, low wear rate;
• Do not require (in most cases) overlays.

• 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.

• Strengthening elements. Aluminum matrix of engine bearing alloys may be strengthened by addition of copper, nickel, chromium, manganese, magnesium, zinc.

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:

• Lead based overlays: 7250-10150psi (50-70 MPa)
• Sputter overlays: 14500-17400 psi (100-120 MPa)

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• Bearings in internal combustion engines
• Engine parameters determining bearing loading
• Lubrication regimes
• Hydrodynamic journal bearing
• Hydrodynamic lubrication theory
• Geometrical parameters of engine bearings
• Mechanisms of wear
• Requirements to engine bearing materials
• Engine bearing fatigue test
• Engine bearing materials
• Copper based bearing materials
• Manufacturing bi-metal strips for copper bearings
• Continuous casting of aluminum based bearing alloys
• Manufacturing bi-metal strips for aluminum bearings
• Lead based engine bearing overlays
• Tin based engine bearing overlays
• Sputter bearing overlays
• Polymer based engine bearing overlays
• Engine bearing failure
• Selection of engine bearing materials
• Effect of low viscosity oils on engine bearings
• pMax Black™ - Strengthened Tri-metal Bearing Materials for High Performance Bearings
• U-Groove™ Modified Design of Oil Groove for High Performance Bearings
• ElliptiX™ Oil Hole of New Design for High Performance Bearings
• EccentriX™ Optimal Eccentricity for High Performance Bearings
• RadiaLock™ - Design of Crush Height for Reliable Press Fit of High Performance Bearings
• Modern Trends In Materials For High Performance Engine Bearings
• Optimization of Clearance Design for High Performance Engine Bearings
• Camshaft Bearings
• Ecological Aspects Of Engine Bearings
• Consistency in Bearing Wall Thickness
• Soft Strength of Racing Bearings
• Effect of oil viscosity on hydrodynamic friction of engine bearings
• Bearing Materials For Race Engines
• Oil Clearance and Engine Bearings
• Polymer Coated Bearings
• Development of Performance Bearings for Race Engines of Modern Design
• Failures of Engine Bearings and their Prevention
• Engine Bearing Housing and How it Affects Engine Bearings
• Polymer Coatings for Race Engine Bearings
• Heavy Duty Engine Bearings - Materials, Geometry, Failures
• Hydrodynamic Bearing – Calculations and Design
• Geometry of Engine Bearings
• Crush Height of Engine Bearings
• Materials for Engine Bearings
• Cast aluminum alloy 852.0

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