Effect of Test Temperature on Fatigue Behaviour in AC4CH Cast Aluminium Alloy
Yoshihiko UEMATSU, Keiro TOKAJI and Norihiko HASEGAWA
Abstract:Fully reversed axial fatigue tests were conducted using plate specimens of a cast aluminium alloy, AC4CH, at three different temperatures of room temperature (R.T.), 150 (423K) and 250 (523K), and crack initiation and small crack growth were studied in detail by means of replication technique. At 150 and 250, fatigue strength was nearly the same as, or significantly lower than, at R.T., respectively. The fatigue strength characterized in terms of fatigue ratio, /B, was the same at all temperatures in high stress region, but slightly lower at 250 in low stress region. Cracks invariably initiated from a casting porosity at R.T., while crack initiation due to slip deformation became dominant at elevated temperatures. At 250, a number of cracks were initiated due to slip deformation and the coalescence of the main crack and other cracks occurred very frequently, particularly in low stress region. At a fixed maximum stress intensity factor, Kmax, small crack growth rates were faster with increasing test temperature. When characterized in terms of Kmax/E (E: Elastic modulus), crack growth rates became similar at R.T. and 150C, but still faster at 250. It was indicated that such enhanced crack growth at 250 was attributed to most frequent coalescence of the main crack and other cracks, resulting in the lowest fatigue strength at this temperature. Key Words:Fatigue, Cast aluminium alloy, Elevated temperature, Crack initiation, Small crack growth