Production of ultrafine microstructures in Al-Sn, Al-Sn-Cu and Al-Sn-Cu-Si alloys for use in tribological applications

AI-Sn, Al-Sn-Cu and AI-Sn-Cu-Si alloys are employed in the production of shell bearings for use in automotive engines. These bearings are normally produced by casting and roll bonding on to a steel backing. An alternative direct form of manufacture has been developed using high velocity oxy-fuel sprayed (HVOF) coatings of these alloys on to the steel. Examination of as-sprayed deposits has revealed that they have nanoscale tin particles evenly distributed throughout the Al matrix. The addition of Cu changes the size and distribution of the Sn particles. Alloys were then subjected to heat treatment at 208 degrees C, 300 degrees C and 450 degrees C to study the process of Sn particle coarsening. On heat-treatment at 450 degrees C sub-micron Si precipitates were also found in the Si containing alloys. Heat treated microstructures were compared with those of roll bonded materials and were found to have a much finer grains and Sn particle size after heat treatment. Tests which impose fatigue damage on the shell coating have indicated some promise for this new form of bearing manufacture.