Time-resolved x-ray imaging of aluminum alloy solidification processes
- PDF / 1,830,306 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 182 Views
INTRODUCTION
DEMANDING applications in the automotive industry call for aluminum castings to be mass produced without casting defects. Predictive models for heat and fluid flow are successfully being used in the design of components and casting processes, but the ability of those models to quantitatively predict casting defects such as porosity and hot tearing is limited. One example is the calculation of interdendritic feeding, which is essential in many types of casting-defect modeling. This requires accurate values of the interdendritic permeability, which is a function of the fraction and morphology of the dendrite phase.[1] Existing models for dendritic growth do not predict morphological parameters with sufficient accuracy for reliable permeability calculations.[2] The present lack of knowledge of the morphological development of aluminum alloy microstructures during solidification is, thus, prohibitive for the development of the sophisticated casting models that are needed in the aluminum foundry industry. Several experimental methods have been used to investigate how the microstructure develops during solidification. A metallographic investigation of the solidified material shows a microstructure which has transformed and coarsened during the solidification and subsequent cooling, and it is often difficult to conclude how the growing crystals have evolved during the early stages of solidification. Quenching of the microstructure during solidification results in a substantial refinement, and this method has been used in order to “freeze” the microstructure. Subsequent metallographic investigation shows a coarse structure, which is assumed to be representative of the solid at the moment RAGNVALD H. MATHIESEN, Research Scientist, is with SINTEF Materials Technology, N-7465 Trondheim, Norway, Contact e-mail: [email protected] LARS ARNBERG, Professor, Department of Electrochemistry and Metallurgy, and KJELL RAMSØSKAR, Retired Research Scientist, Department of Physics, are with the Norwegian University of Science and Technology, N-7491 Trondheim, Norway. TIMM WEITKAMP, Ph.D Student, CHRISTOPH RAU, Postdoctor, and ANATOLY SNIGIREV, Beamline Scientist, are with the Experiments Division, ESRF, F-38043, Grenoble, France. Manuscript submitted October 3, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
of quenching, and a fine microstructure which is assumed to represent the melt. Transient phenomena in the destabilization of the growing microstructure subsequent to the quenching, however, result in a gradual transformation from the coarse to the fine microstructure, and this often leads to errors such as e.g., an over estimation of the fraction of solid.[3] Another method to obtain an impression of the microstructure during solidification is decanting or drainage of the melt during solidification and subsequent investigation of the solidified crystal network. Drainage sometimes takes place naturally in aluminum castings due to insufficient feeding, but it can also be promoted. This method, however, is limit
Data Loading...
