Development of Bearing with Multilayer Bi-Sb Overlay for Automotive Engines 2023-01-0872

In recent years, the removal of lead (Pb), which is an environmentally hazardous material often used in bearings for automotive engines, has been continuously promoted. Bismuth (Bi) is attracting attention as a substitute for lead, and it is currently being used mainly for passenger cars and trucks as a lead replacement. However, lead has not been replaced for motorcycles where the bearings are exposed to high temperatures at high rotation speeds, and trucks and generators where high loading capacity, long lifetime and good corrosion resistance are required. It has been difficult to achieve both high load and corrosion resistant for a bearing overlay material. The purpose of this development is to improve the corrosion resistance and fatigue resistance of bismuth overlay by developing a bismuth- antimony alloy overlay in which antimony (Sb) is added to the bismuth matrix. However, concern arises that antimony may form a compound with copper (Cu) in the bearing alloy underneath the overlay therefore adversely affects the corrosion resistance and fatigue resistance of the overlay. The target of this study is therefore to optimize the bismuth - antimony overlay so that excellent corrosion resistance and fatigue resistance can be achieved while the formation of copper and antimony compounds is suppressed. To reach the development target, various experiments were carried out focusing on antimony concentration and structure of the bismuth - antimony overlay. In the developed material, the formation of copper-antimony compounds was suppressed, and the oxidation resistance and fatigue resistance were superior to other materials. After excellent rig test results, more practical evaluations such as actual engine test will be conducted.