Einfluss von Eisenverunreinigungen auf das Versagensverhalten von Al-Guss-Legierungen
Förderung durch das Land Hessen im Rahmen von LOEWE – LandesOffensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz
Introduction
The use of the recycled Al-Si-Cu alloys for the production of structural parts has received a considerable amount of interest in recent years since secondary alloys can significantly reduce production costs as well as the CO2 emissions associated with the production of primary aluminum. However, the recycling process of the aluminum alloy leads to the accumulation of iron, which causes the formation of brittle Fe-rich intermetallic inclusions. The aim of this work is to study the influence of the Fe-content of the damage behavior of an Al-Si-Cu alloy by X-ray tomography. Fatigue tests were conducted and the fracture surfaces were analyzed by scanning electron microscopy as well as X-ray tomography in order to analyze the crack initiation and propagation processes.
Material experiments
Fatigue specimens were cast by gravity die casting at a melt temperature of 760°C in a steel mold pre-heated at 350°C. A high resolution lab X-ray tomograph [ZEISS Xradia Versa 520] was used for the three-dimensional measurements of the casting defects and fracture surfaces. Fatigue tests were performed and the fracture surfaces were subsequently analyzed by scanning electron microscopy and micro-computed-tomography with the aim of classifying the different fracture damage scenarios and characterizing the fatigue behavior.
Results
The fracture surfaces show different characteristic damage mechanisms at different ranges in the probability distribution of the lifetime from the alloy with 2.28% Fe content (see Fig. 1).
Fig. 1: Classification of the damage mechanisms in the statistical distribution of the fatigue cycles from 2.28% Fe content specimens.
Fig. 2 shows high volume fraction and size of shrinkage pores that interacted with the surface crack that caused the failure. It can be observed that the shrinkage pores are surrounded by large ß-Al5FeSi particles between the dendritic arms in zone near the fracture surface.
Fig. 2: 3D reconstruction of the ß-Al5FeSi inclusions located between the dendritic arms of the shrinkage pores located under the fracture surface.