Microstructure and superplasticity in Al-Mg alloy composites reinforced with silicon nitride particles

The microstructure of Al-Mg alloy composite reinforced with α-Si₃N₄ particles was investigated. Matrix grain boundaries were segregated with Si, N and O, and contain no secondary phases. On the other hand, matrix/reinforcement interfaces contain Mg₂Si, MgO, and Al₂MgO₄. X-ray energy dispersive data also indicated a gradual variation of the N concentration across the reaction zone and enrichment of Mg at the interface between the matrix and the reaction zone. In situ TEM observation using a heating stage revealed incipient melting along grain boundaries and interfaces at 827 K. A liquid pocket was also observed at triple junctions. A good agreement in incipient melting temperature was obtained between TEM and DSC results. A possible role of the liquid phase in the superplasticity is discussed.