Influence of Microstructure on the Quasistatic and Low Cycle Fatigue Behaviour of an AA2618 Aluminium Alloy.

Abstract: The high-strength aluminium alloy AA2618 is a typical material to manufacture centrifugal compressor wheels of exhaust turbochargers. In general these components are manufactured from heat treated forged slugs. Depending on the size of the slugs during the heat treatment different microstructure may arise. Especially for large slugs the emerging microstructure will not be uniform within the manufactured component. For this reason, the mechanical properties of the material will depend on the location within the component. To investigate this effect a T6 heat treated forged slug measuring 530mm in diameter and 200mm in high was investigated. From the metallographic investigations and from measurements of the hardness three different regions could be defined. Specimens were taken from different locations and their behaviour in tensile tests and low cycle fatigue tests were determined. It turns out that the yield strength depends on the grain size. This behaviour can be described using a Hall-Petch relation. The low cycle fatigue behaviour, the lifetime and the development of fatigue damage are influenced by the local microstructure. The reduction in the lifetime correlates with the number of subgrains. [Copyright &y& Elsevier]