Volume 80, Issue 3

Heat treatments are generally used to adjust the required material properties at certain positions in the component, particularly at geometric notches where high stress concentrations are present due to the geometric form factor. During the hardening of steel components in evaporating liquid media, the quenching process can lead to significant variations in local material properties due to inhomogeneous cooling behavior. The geometry of the component – size, shape (e. g., geometrical notches), and surface roughness – directly impacts the cooling behavior. Geometric notches, in particular, change the surface area to volume ratio, which affects local cooling rates and must be assessed for design considerations. It is crucial to compare local stress at the notch base to relevant material standards to ensure component safety under specified loads. Following the definition of the geometric form factors, a thermal form factor model is developed in the present work, which describes the cooling in the notch base. The thermal form factor relates the t 8/5 -times in the notch base to the t 8/5 -times at the unnotched surface, giving insight into locally expected material properties. Experimental investigations on austenitic steel, unnotched and notched cylindrical samples are presented which show the influence of the notch during quenching in oil.

This publication investigates the influence of quenching velocity on the supersaturation of the solid solution state of the alloy AlSi9Cu3. The basic subject of these investigations are samples from a four-cylinder crankcase, cast in the laminar die-casting process. With regard to the examination methodology, two different implementations of solution annealing are used on specimens in the format of an M8 tensile specimen: Short-term solution annealing by means of diode lasers, which minimizes the influence on the casting structure and allows different cooling variations, as well as the conventional method of furnace solution annealing for very slow cooling rates of 0.1 °C/s. The samples are then cooled to room temperature after solution annealing and then subjected to artificial aging in the furnace (180 °C | 4 h). The subsequently determined R p0.2 yield strengths are correlated with the cooling rates, which allows the different precipitation behavior to be represented. Finally, the R p0.2 yield strength is set as a function of the cooling rate based on a mechanical material model.

The vacuum brazing process has significant advantages compared to atmospheric brazing processes. Especially the fluxfree joining is a big benefit because removing flux after the brazing process is almost impossible. To reach the highest quality standards of the final product, the cleaning process prior to the brazing process is essential. Using a modified alcohol as a cleaning agent in a cleaning machine running under vacuum allows the solvent to reach cleaning temperatures much higher than its flash point. This causes perfect cleaning results with high surface tension as well as best drying results before the parts leave the cleaning machine after the cleaning process. This paper will explain the solvent cleaning process under vacuum, the cleaning effect, testing options, healthy, safety and environmental issues and case studies showing good and bad cleaning results.