Microstructure and tensile properties of composites with high strength aluminium alloys matrix reinforced with SAFFIL fibers
Jerzy Morgiel, Krzysztof Naplocha, Małgorzata Pomorska, Jacek Kaczmar
Quarterly No. 2, 2011 pages 136-141
DOI:
keywords: MMC, AA2024/ Saffil AA6061/ Saffil AA7075/ Saffil nano-composites
abstract Metal matrix composites (MMC) were produced by the force infiltration of Saffil fiber preforms with high strength AA2024, AA6061 and AA7075. The preforms with ~10 vol.% of fibers were bonded by dipping in liquid glass and heat treated at 800oC/2 hours. Next, the preforms were placed in a mould and the liquid alloy was forced into it. The composites microstructure was investigated using scanning xL30 and transmission Tecnai FEG (200 kV) electron microscopes. The tensile strength was tested with an Instron machine. The microstructure observations confirmed that after heat treatment, the Na2SiO3(H2O) binding phase turns to amorphous silica. The liquid AA2024 reacts with the silica, substituting part of the binder with a fine-crystalline mixture of MgO, Cu2Al and silicon crystallites. The AA6061also reacts with the SiO2 binder, but replaces it with a porous amorphous aluminium oxide. However, the infiltration with AA7075 left the binder mostly intact with discontinuous precipitates of MgO at the silica/matrix interface. The mechanical tests of the AA6061/Saffil were inconsistent due to a large scatter of results, but for the other composites they showed that the Saffil fibers helped to increase the tensile strength of the castings from 230 to 330 MPa and from 420 to 590 MPa for the AA2024/ Saffil and AA7075/ Saffil composites (T6 conditions) respectively.