DescriptionAfter casting and solidification, Al-cast cylinder heads undergo a sequence of heat treatments to achieve creep resistance for the service condition. This sequence comprises solution heat treatment, quenching and artificial aging. During quenching to room temperature internal stresses form within the complex geometrical structure of the cylinder heads due to temperature gradients. These internal stresses affect negatively the performance of the product, and can be total/partially reduced during the aging treatment. This work focuses in the description and modelling of the relaxation of the stresses occurring simultaneously with the precipitation of stable and metastable θ, β and Q-phases in the temperature range between 180-230°C. The model couples the relaxation of the stresses due to the increment of the temperature with the strengthening/softening produced by the precipitation/coarsening of the precipitates. The relaxation is modelled phenomenologically as an exponential decreasing function based on the work of Rahimi et al., also taking the interaction of dislocations, vacancies and interface friction into account. The microstructural changes due to precipitation are modelled using MatCalc® software toolkit to obtain information about type of precipitate, their sizes, fractions and number densities. The MatCalc® simulations are compared and evaluated with results of Microhardness Testing, Differential Scanning Calorimetry (DSC), Scanning and Transmission Electron Microscopy (SEM & TEM) investigations. The model is validated with several relaxation tests performed on the Gleeble ® 3800 thermomechanical testing machine and on a dynamic mechanical analysis (DMA) device using samples in T4, T6 and several intermediate precipitation states.
|Period||26 Oct 2020 → 29 Oct 2020|
|Event title||17th International Conference on Aluminium Alloys|
|Location||Virtuell, Grenoble, France|
Fields of Expertise
- Advanced Materials Science