Towards Closed-Loop Recycling of Ceramic Particle-Reinforced Aluminium Alloys: Comparative Study of Resistance-Heating Sintered Primary and Solid-State Recycled Secondary SiCp/AlSi7Mg Composites

Abstract

Particle-reinforced aluminium matrix composites (AMC) with a high-volume fraction of ceramic reinforcement (>30 vol.%) combine high specific strength and stiffness with good wear resistance and thermal stability, resulting in their increasing popularity in high-load applications, such as brake discs and bearings. It is hence assumed that AMC will accumulate as scrap in the near future. Appropriate recycling strategies must therefore be developed to maintain AMC’s inherent properties. Melt-metallurgical recycling routes bear the danger of dissolving the ceramic reinforcement in the liquid metallic matrix and contaminating primary melts or forming intermetallic phases in secondary melts. Here, a solid-state AMC recycling route with crushing and sintering is investigated, wherein all steps are carried out below the solidification temperature of the aluminium matrix. A sintered primary AMC is mechanically converted into a particulate/powdery secondary raw AMC in coarse, medium, and milled quality (i.e., with d ≈ 7–12 mm, d ≈ 3–7 mm, and d < 300 µm) and subsequently resistance heating sintered to a secondary AMC under a variation of the sintering pressure. The two AMC generations are analysed and discussed regarding their microstructure and mechanical properties. Since the secondary AMC show reduced the mechanical strength, the fracture surfaces are analysed, revealing iron contaminations from the mechanical processing.