Effects of artificial aging on precipitation behavior, mechanical properties and corrosion resistance of Si3N4/6061Al composite fabricated by sintering and hot extrusion processes

Abstract

Artificial aging plays important roles on the final performances of the manufactured components of Al matrix composites, and it is of great importance to find the appropriate aging parameters to obtain a good combination of mechanical properties and corrosion resistance. In this study, the Si3N4 particle reinforced 6061Al (Si3N4/6061Al) composite was produced by sintering and hot extrusion, and both single and two-step aging were carried out to examine the precipitation behavior. It was found that the grain structure of Si3N4/6061Al and 6061Al did not show a notable change after solution treatment, while Mg element inclined to concentrate at the Si3N4/6061Al interface. The compounds containing Mg and Cu formed at Si3N4/6061Al interface during aging process, and β″ and β′ phases precipitated after peak and two-step aging, respectively. β″ phase contributed to improving the hardness, strength and wear resistance, while β′ phase caused an opposite trend. The Si3N4 particles could also enhance the mechanical properties due to the load transfer and dislocation strengthening. The samples treated by solution exhibited the best corrosion resistance, while the peak-aged ones were sensitive to intergranular corrosion owing to the continuously distributed precipitates and the precipitate free zones at grain boundaries, and two-step aging could alleviate the intergranular corrosion susceptibility. Due to the preferential dissolutions of Mg element in Mg-containing layers and Mg/Cu-containing phases, the Al matrix around Si3N4 particles was seriously corroded.