A Study of Lead-free Al-Zn-Si Alloy Bearing with Overlay for Recent Automotive Engines

Recently, a lead-free Al-Sn-Si alloy bearing with metallic overlay has started to be used for a portion of automotive engines. This bearing has good anti-seizure and excellent running-in properties, and is an environmentally friendly alternative to the current copper-lead alloy with lead based overlay in accordance with the ELV regulation for the removal of lead from bearings. But automotive engines have been required to exhibit higher performance in order to enhance their commercial power, which tends to require the engine bearing to perform under higher temperature due to higher specific load on the bearing and higher rotational speed of the crankshaft. It is clear that the current lead-free aluminum alloy bearing is not satisfactory with respect to fatigue strength in some cases, and requires higher strength under the higher temperature conditions. Based upon this background, a new lead-free aluminum alloy bearing with metallic overlay has been developed, which is an Al-Zn-Si alloy bearing with a plated bismuth overlay via a silver interlayer for securing a good running-in property. This paper describes performance and other details of this newly developed bearing verified through bearing rig tests and engine tests.