Fatigue Strength of Al Cast Alloy in Bio-Diesel Fuel

Abstract

In order to investigate the effect of bio-diesel fuel (BDF) on fatigue strength of a squeeze cast Al alloy, AC4CH-T6, rotating bending fatigue tests were carried out using plain specimens in BDF made by rapeseed oil. The results were compared with those in turbine oil and in ambient air. Fatigue life was longer in turbine oil and shorter in BDF than that in ambient air. Fatigue life in each environment tested was mainly occupied by the growth life of a crack smaller than 1mm, meaning that the difference in fatigue strength affected by environment was mainly yielded in the growth process of a small crack. The crack growth rates were suppressed in turbine oil and accelerated in BDF in comparison with those in air. BDF contained much water dissolved from air in the early stage of fatigue process. The suppression of crack growth was caused by wedging effect of oil and the acceleration was caused by corrosion due to dissolved water in BDF, which was larger than the suppression due to the wedging effect.