Composite coating

Aluminium metal is used extensively in our modern world. Often in the manufacture of aluminium products, the molten metal is poured into dies of the required shape. The dies are made of steel and, over time, suffer surface damage.

Asma Salman, a PhD student at the University of Waikato, has been investigating this problem.

Along with her supervisor, Dr Brian Gabbitas, she explains how plasma spray-coating the dies with a titanium-based powder composite can inhibit surface damage and extend the life of the dies.

Point of interest What is plasma spray-coating?

Transcript

ASMA SALMAN My research is focused on titanium-based composite materials for the metal die-casting industries. A die is actually a mould in which we put molten aluminium – and it’s just like similar to the process of making jellies in the mould – and when the molten metal solidifies, we bring it out from the die, and it has just the same shape as the mould. Molten aluminium is going to stick with the dies, and after a number of cycles, molten aluminium starts sticking and it ultimately results in die failure. And dies cost approximately more than 1,000 dollars, US dollars, so it’s a very valuable thing for the industry people. So we are looking for an appropriate coating which can increase the life of the dies and will ultimately become of benefit to the industry. So we are going to apply these titanium-based coatings, particularly by a thermal spraying technique.

DR BRIAN GABBITAS Well thermal spraying is where the powder is fed into a high velocity, high temperature jet, and it flows with the jet onto the material that one is trying to coat and produces a layer of composite powder onto the material.

ASMA SALMAN The biggest advantage of this kind of spraying technique is that it provides adhesion and low porosity to the material, the coating material.

DR BRIAN GABBITAS We have had success with our composite coating and the work we've doing with finding a coating resistant to attack by molten aluminium. We need to do many, many more industrial trials in different situations to ascertain whether this is fully successful, but early indications – particularly with work that we have done with Fletcher Aluminium – suggest that the coating looks promising. We may have some modifications to do, we may have to change the way that we deposit the coating and use other spraying techniques, but yes we’ve had numerous successes to date.

Acknowledgements: Kerry Loewen Pulpolux (Mexico)