Controlling porosity in shaped castings
An industrial and scientific challenge
L. Arnberg‡, R. Helenius‡, M. M’Hamdi*, Ø. Nielsen*, T. Magnusson#, A. I. Voll‡
‡ #
Norwegian University of Science and Technology *SINTEF Materials Technology Icelandic Alloys, Iceland
Why porosity?
• Porosity is a critical defect affecting the mechanical
performance of shaped castings (Figure 1).
• Shaped castings are commonly x-rayed after
production. Percentage of porosity-rejects is one of
the most important figures of merit in a foundry. (a) (b) (c)
• An improved control of porosity will: Figure 1. (a) Macroporosity, (b) and (c) microporosity (insufficient
feeding and gas pore precipitation, respectively).
− Increase the profitability in foundries.
− Increase the market potential of shaped castings
by improving their mechanical performance.
Challenges
• Mathematical models capable of predicting porosity
distribution are needed in the design and process
choice for new components.
• Knowledge and quantification of key mechanisms
responsible for the nucleation and growth of
porosity are needed in order to:
− Develop alloys less susceptible to porosity.
− Optimise grain refiners/modifers (trace elements).
− Choose the optimum melt treatment/mould filling.
• Objective criteria for automatic rejection of castings Figure 2. Comparison of measured and calculated porosity
based on x-ray images are needed in order to fraction in a directional solidification experiment.
minimise loss due to too large safety margins.
What did we achieve so far?
• Cutting-edge simulation software for prediction of
porosity acquired (calcosoft by Calcom and Ecole
Polytech. Federale de Lausanne, EPFL).
• Effects of hydrogen, inclusions, and feeding
conditions on porosity studied with calcosoft, and
compared with experimental results (Figure 2).
Figure 3. Gravity die casting experiment used to study porosity
• Gravity die casting experiment (Figure 3) for and mechanical properties in shaped castings.
studies of porosity and mechanical properties
developed and thoroughly tested.
How do we proceed?
• Calcosoft predictions of porosity in mass produced
cast automotive components (Figure 4).
• Extensive study of the effect of trace elements
(H, Ca, Sr, Na, P, etc.) and melt treatment on
porosity distribution and mechanical properties.
• Measurements of feedability and permeability. Figure 4. Calosoft simulation of the porosity distribution in an
• Optimisation of alloys and process praxis. aluminium wheel produced by high pressure die casting
• Improved productivity and competitiveness. (courtesy of C. Pequet, EPFL).
Contact info:
Oyvind.Nielsen@sintef.no
NorLight Shaped Castings of Light Metals