The Fraunhofer Institute for Nondestructive Testing IZFP in Saarbrücken has developed »AloX«, a measurement system that enables the rapid, durable and precise determination of the degree of non-metallic inclusions in aluminium melts. The system has been awarded the Joseph von Fraunhofer Prize and addresses a central problem in aluminium casting: non-metallic inclusions have a decisive influence on the quality of the resulting components, an issue further intensified by the increasing use of secondary aluminium.
In times of scarce resources and strict climate targets, aluminium is becoming increasingly important as a material. It can be recycled with low energy input and offers a combination of properties – low weight combined with good strength – that makes it indispensable for many fields of application, including lightweight construction.
A sufficiently high material quality is decisive for the safe and sustainable use of aluminium. The aluminium melt should be as pure as possible, since foreign substances in the form of particles later have a negative effect on component properties. These mostly non-metallic inclusions reduce the mechanical properties, as they act like notches or incipient cracks in the component. Particularly in the automotive industry and in aerospace, the resulting material damage can have serious consequences. Early identification of inclusions in the melt prevents them from entering the finished component. Previous approaches for detecting particles in melts were either too time-consuming, too expensive, inaccurate, not reproducible, or could only be carried out by experts.
Ultrasonic Backscattering as a Methodological Approach
The AloX measurement system is based on an ultrasound-based approach and detects impurities already during production in the aluminium melt. It relies on the principle of ultrasonic backscattering: ultrasound is coupled into the aluminium melt and the reflected ultrasonic components are detected. In this way, the number, size and distribution of the inclusions can be qualified.
AloX is flexible in use and can perform measurements both in the launder and in the crucible. The system can also be used in difficult measuring positions, enabling continuous monitoring of melt quality. Operation does not require expert knowledge, allowing measurements to be carried out by the staff in the foundry.
Perspectives for Further Melts
As a next step, the researchers are planning to expand the technology of the measurement system. »What works in aluminium melts could also work in other melts. For the time being, we are primarily focusing on low-melting alloys, above all magnesium, tin and zinc, which all lie in the range below 600°C. In the long term, however, steel could also be considered as a target melt«, explain Dr. Thomas Waschkies and Andrea Mroß.
