Influence of the Casting Process in High Temperature Fatigue of A319 Aluminium Alloy Investigated by In-Situ X- Ray Tomography and Digital Volume Correlation

In order to satisfy the economic constraints together with environmental requirements, the automotive industry has been forced to adopt a strategy of down-sizing, which has led into process modification of some engine parts like cylinder heads. Nowadays, the Lost Foam Casting process (LFC) replaces the conventional Die Casting (DC) process due to cost reduction and geometry optimization goals. However, aluminum alloy automotive parts produced by the LFC process have a coarser microstructure and more porosity defects than parts produced with conventional casting processes at faster cooling rates. In the cylinder heads produced by the LFC process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence of this complex 3D microstructure on fatigue crack initiation and propagation, an experimental protocol using laboratory, synchrotron tomography, SEM images and 3D Digital Volume Correlation (DVC) has been used. Fatigue tests performed at temperatures characteristics of in-service conditions (250°C) revealed the initiation of 3D cracks at large pores and a propagation along the hard inclusions around the main pore that drove to failure but also in other areas of the specimen gauge length.