Despite their widespread technical applications, brass alloys remain a niche topic in materials science compared to typical construction materials like steel or aluminium. The influences of their partially complex, multiphase material structure are hardly documented in technical literature. This thesis contributes to a deeper understanding of the microstructural influence on the material behavior of CuZn alloys by characterizing their microstructure and correlating it with fundamental mechanical properties. The focus lies on an unidentified brass casting alloy used in a component for heavy machinery construction.
Metallographic sections were prepared, etched and the constituents of the microstructure were identified using light microscopy images aided by chemical analysis methods (optical emission spectrometry and EDX). Subsequently, the microstructural elements were quantified in terms of geometry (size, morphology) and their distribution across the components cross-section using (semi-) automated image processing and evaluation algorithms. In addition, quasi-static tensile tests were conducted, and the determined characteristic values were used to describe the materials behavior.
The present coarse-grained multiphase microstructure exhibits micro blowholes, gas pores, and iron precipitates of different morphology (dendritic and plate-like), which are unevenly distributed over the cross-section due to segregation. No preferred orientation is observed, and the microstructure is isotropic.
Due to locally increased cooling rates and gravitational segregation of the nucleation-promoting iron precipitates, the sections in the lower cross-sectional area exhibit grain refinement with globular precipitates of the α-phase, whereas needle- and plate-shaped α-particles are present in the coarse-grained area. A strong correlation exists between the mechanical properties determined in the tensile test and the microstructural changes. In the fine-grained region, with dispersed precipitates, both strength and fracture strain increase. The investigated alloy consistently exhibits ductile fracture behavior with shear fractures oriented towards the maximum shear stress, as well as localization of failure in the presence of large defects. However, a separate analysis of the influences of individual microstructure constituents is not feasible based on the present results and the evaluation is limited to trend-based statements.
The established methodology, however, with its comprehensive description of the microstructure elements and their distribution, lays the foundation for further investigations to describe the material behavior and thus, it facilitates the understanding of the interplay between manufacturing conditions, microstructure, and material properties in the present material, and can be applied to other CuZn alloys.