Modeling creep damage of an aluminum-silicon eutectic alloy

Aluminum-silicon casting alloys are widely used in the automotive industry. The aim of this article is to analyze creep and creep damage of the eutectic AlSi12CuNiMg cast piston alloy and to present a constitutive model that reflect basic features of deformation, aging and damage behavior. Creep tests and force-controlled low cycle fatigue tests are carried out at several levels of temperature. Creep curves exhibit classical three stages. The tertiary creep stage is controlled by damage processes, mainly due to failure of the brittle inclusions and aging processes of the aluminum matrix. Ruptured specimens are analyzed with the help of optical and scanning electron microscopy to establish the fracture mode. A constitutive model is developed to describe the high temperature creep and ratcheting behavior. The proposed model involves three state variables including a back stress, an aging parameter and a damage variable. The model is calibrated against the creep and tensile curves and verified by numerical simulations of cyclic creep tests.