Optipor - Investigation of the nucleation mechanisms of gas pores for reproducible adjustment and optimization of the porosity profile in Al-Si cast alloys to increase the resistance to fatigue damage in the range of very high load cycles

  Fatigue crack in an Al-Si-casting alloy Copyright: © IEHK Fatigue crack in an Al-Si-casting alloy

Lightweight components made of cast aluminum materials have long been the order of the day, especially in the automotive industry. During the casting process, pores or blowholes form in the structure. Due to their stress-increasing, crack-like character, these can have a negative effect on fatigue properties. The elimination of porosity by hot isostatic pressing is uneconomical and would significantly increase the unit costs. In contrast, the setting of a defined porosity profile with homogeneously and finely distributed round gas pores is promising. Currently, however, the pore formation mechanisms are insufficiently understood to set reproducible porosity profiles. Therefore, higher safety factors are currently used to exclude the failure of the component. With the help of special nucleation patterns, the shrinkage deficit is distributed homogeneously and a strong expression of shrinkage porosity is prevented. This increases the fatigue strength and at the same time reduces the scatter of properties. The usual crack initiation sites are shrinkage deficits in the form of pores. As soon as the pores are no longer the crack initiation location as a result of fatigue, the microstructural influence on crack initiation and crack propagation can be investigated. By using special laboratory equipment, the locations where fatigue cracks (cf. Fig. 1) occur can be localized even before micro- and macroscopic crack initiation.

The overall research goal of the Optipor project is on the one hand to understand the nucleation mechanisms of gas pores and their formation. On the other hand, a damage mechanism based material model is created by determining fatigue properties in dependence of the set porosity and microstructure. On the production side, the research goals reduce reject rates and costs, save resources and thus ensure sustainable production. On the user side, the potential for lightweight construction and thus efficiency can be increased by reducing safety factors.