These materials were developed as an improvement on the white metal and copper based alloys and to provide bearings that carry high loads. Special features include good resistance to corrosion, high thermal conductivity,and high fatigue strength. The disadvantages are only moderate embedding properties, poor compatibility ,and high coefficients of thermal expansion. If used as solid unbacked bearings this type of alloy is usually too weak to maintain an interference fit and too hard to run satisfactorily against an unhardened shaft. As a bearing material unalloyed aluminum has a tendency to seize to a steel mating surface. It was found that 20% of tin added to the aluminum improved seizure resistance and that cold working and annealing helped to prevent brittleness. The difference in coefficients between aluminum and steel necessitates work hardening the bearing before use to prevent loosening in service.