Complexly shaped components, for example used in aircraft, automobiles or in aerospace technology are often manufactured in a metal powder injection molding process. In the sintering process, plastic is added to powder with a steel or titanium content, pressed into the desired form and then baked together at high temperatures.
Up until now, this method has been unsuitable for aluminum, due to the fact that the oxide layer arising around the aluminum particles could only be removed in extreme heat. At the same time, the melting point of the light metal is relatively low, which limited the maximum sintering temperature. The oxide layer could not be removed before the metal melted. In addition, the carrier substance could only first be removed at higher temperatures.
Researchers at the Institute for Chemical Technologies and Analytics at the Vienna University of Technology now circumvented these problems by creating an oxygen-rich atmosphere in the sintering furnace. “The aluminum oxide layer in the particles is so dense that they protect the particles against complete oxidation. At the same time, the oxygen helps in the burning the carbon contents of the binding materials”, said the chemist Christian Gierl-Mayer.
Following this first step, they replace the oxygen with nitrogen and further increase the temperature. With the help of magnesium, the aluminum oxide layer is ultimately broken down, the material liquefies and the metal piece is sintered. The researchers have already submitted a patent application for the process.