Einfluss der Mikrostruktur auf das Kurzzeitfestigkeitsverhalten von AlSi-Gusslegierungen

Translated title of the contribution: Microstructural impact on the low cycle fatigue behaviour of AlSi cast alloys

Michael Pegritz

Research output: ThesisMaster's Thesis


Modern automotive industrial designs are often utilized as cast AlSi components in hybrid, or electrical, powertrain applications. They enforce a complex geometry to satisfy the technical, and economical, demands. The task of service strength based design of such cast aluminium alloys has been well researched recently, focussing on threshold based approaches to assess the endurance strength. But the finite life strength, depend on the manufactured local microstructure, is still an interesting field of research. The main contribution of this thesis is the investigation of the microstructural impact on the low cycle fatigue behaviour of Sr refined, peak-aged AlSi8Cu3 at room temperature. To achieve this, four different sample series have been manufactured from serial components. Samples with coarse and fine dendrite-arm-spacing as well as varying micro-porosity were studied. Moreover, for both microstructures, pore-free hot isostatic pressed (HIP) sample series are evaluated as material reference condition. A significant increase in ductility as well as low cycle fatigue strength is feasible by additional HIP-treatment for coarse microstructure specimen, whereat the finer grained microstructure showed only marginal improvement. Fracture of persistent slip bands along the {111}〈110〉-slip system turned out to be the major failure mechanism for the microstructural fine materials, with dimensions up to 5.26mm², which is equivalent to 12% of the test cross section. This complementary cyclic damage mechanism is quite unexpected, as usually the fatigue crack initiates from microstructural inhomogeneity’s, such as shrinkage pores, within the cristallographic grain. As the size of the fractured persistent slip bands varies more pronounced within fine grained microstructure, the deduced fatigue strength exhibits an increased scatter index in case of hot isostatic pressing. For combined fatigue design in the low- and high-cycle fatigue regime the stress based Kohout-Vechet model proved to be an engineering-feasible design tool with a limited number of input parameters. For each sample serie, the dendrite-arm-spacing has been automatically measured by a refined digital image processing tool. Furthermore, a probabilistic Manson-Coffin lifetime-model as well as the Ramberg-Osgood strain-hardening-concept was derived to facilitate a comprehensive characterization in the finite life region. The significantly improved damage mechanism knowledge of cyclic finite-life applications as well as the build-up material database feature now an improved design tool for AlSi casting alloy applications.
Translated title of the contributionMicrostructural impact on the low cycle fatigue behaviour of AlSi cast alloys
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Leitner, Martin, Co-Supervisor (internal)
  • Stoschka, Michael, Supervisor (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until 27-05-2025


  • cast aluminium
  • fatigue strength
  • low cycle fatigue
  • persistent slip band

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