Technische Universität Chemnitz
Particle-reinforced aluminium matrix composites (AMC) are of high interest, due to their high performance properties combined with lightweight potential. Excellent mechanical properties, as good wear resistance, thermal stability as well as high specific strength and stiffness, can be achieved by a high volume fraction of ceramic reinforcement (> 30 vol.%) which enable the application as brake discs. Due to the increasing market share of AMCs, these composites will increasingly accumulate as scrap in the near future. Only laboratory-scaled research activities currently focus on AMC recycling. So for now, smaller undetected AMC fractions are processed together with aluminium scrap via common melt recycling routes. However, due to the high proportion of the reinforcing phase, recovering the matrix aluminium is of minor industrial interest. In addition, there is a risk that the melt is contaminated by the dissolution of the ceramic particles. With increasing particle content and an associated larger, reactive surface, the enhanced formation of reaction phases in the melt increases. These changes in the AMC composition have a significant influence on the mechanical properties. Therefore, appropriate recycling strategies must be researched to maintain the properties of the cost-intensive high-performance material for a resource efficient use. In our study, we investigate solid-state recycling and subsequent powder metallurgical manufacturing as alternative recycling approach. The field assisted sintering technique (FAST) is a robust process that consolidates powders with different particle shapes and size distributions, which is mandatory for the irregularly shaped and sized, recycled AMC powder. In addition, by the FAST process, which requires a process time of just a few minutes, microstructural changes can be avoided in order to maintain the initial material properties. The first successful recycling attempts by consolidation of milled AMC scrap are demonstrated. Differences between the initially FAST-processed and the recycled AMCs are discussed regarding microstructure and mechanical properties.
Abstract
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