Application of a √area-approach for fatigue assessment of cast aluminum alloys at elevated temperature

Abstract

�This paper contributes to the effect of elevated temperature on the fatigue strength of common aluminum cast alloys EN AC-46200 and EN AC-45500. The examination covers both static as well as cyclic fatigue investigations to study the damage mechanism of the as-cast and post-heat-treated alloys. The investigated fracture surfaces suggest a change in crack origin at elevated temperature of 150°C. At room temperature, most fatigue tests reveal shrinkage-based micro pores as theircrack initiation, whereas large slipping areas occur at elevated temperature. Finally, a modified √area-based fatigue strength model for elevated temperatures is proposed. The original √area model was developed by Murakami and uses the square root of the projected area of fatigue fracture-initiating defects to correlate with the fatigue strength at room temperature. The adopted concept reveals a proper fit for the fatigue assessment of cast Al-Si materials at elevated temperatures; in detail, the slope of the original model according to Murakami should be decreased at higher temperatures as the spatial extent of casting imperfections becomes less dominant at elevated temperatures. This goes along with the increased long crack threshold at higher operating temperature conditions.