Erstarrung einer technischen Al-Si-Mg-Legierung in Silica-Aerogelformen

The Observation, detection and control of the form filling and solidification process of metal melts is of great importance for the development of optimized gating systems and perfectly designed microstructures in modern casting technology. In the casting process metal melts are usually poured into moulds which consist of sand, ceramic or metal. The experimental detection of form filling and the essential solidification parameters such as the local temperature gradient, the local solidification velocity and the local cooling rate is difficult. The analysis of real casting processes and their description by models is experimentally complicatetd since the solidification parameters are functions of time and position in the casting. But the detection of the significant solidification parameters with time and spatial resolution is essential for the experimental verification of the so called microstructure models in which the characteristic values of the microstructure are mathematically coupled with the solidification parameters and combined within models. The solidification parameters cannot be detected in-situ and can only be detected with invasive methods during conventional casting in opaque materials. In order to determine the fraction solid (fraction primary phase) which is already solidified in the liquid-solid range of an alloy as a function of temperature one quenches a partially solidified sample in order to freeze the microstructure of the dendritic zone. So far it is not clarified how much the quenching process changes the solidified parts of the microstructure which already existed at the beginning of the quenching process and thus falsifies the determined fraction primary phase. In this work a significant contribution is given to overcome the problems when detecting the form filling and the solidification parameters during conventional casting in opaque moulds by making use of a new mould material, the transparent silica-aerogel. Investigations concerning form filling, testing of the precision of the casting and the usability of silica-aerogel for the casting of light metals were carried out in this work. The significant solidification parameters are optically detected at various locations of the casting. The lower part of the mould always consisted of silica-aerogel with a wedge shaped mould, whereas at an opposite surface the cooling conditions were varied using different materials. For all experiments a technical Al-Si-Mg alloy was used. The characteristic properties of the microstructure such as the secondary dendrite arm spacing and the spacing of the irregular eutectic are correlated with the solidification parameters. Numerical simulations of the whole process (form filling and solidification) were carried out with the commercial FEM code ProCAST. The results are compared with experimental results of the form filling, the temperature field and the microstructure observed. The central point of the work is the comparison between the optically detected fraction solid and theoretical microstructure models, where the fraction solid was detected in-situ as a function of temperature with non-invasive or thermoanalytical methods for the first time.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Tscheuschner, Dirk

Contributors dc:contributor

• Ratke, Lorenz

• info:eu-repo/classification/ddc/620
• Ingenieurwissenschaften

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-119044%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:56972