Microstructure and compressive property of in situ Mg 2Si reinforced Mg-microballoon composites

The in situ Mg 2Si particles reinforced AZ91-microballoon composites were fabricated by preforming pressure-infiltrated process using hollow flyash cenospheres (FAC, 180-250 μm) as the preform. The microstructure and chemical components of the composites were observed and analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The compressive properties were investigated by compression test. The fracture mechanisms of the composites were concluded by fractography observation. The experiment results show that the FAC distributed homogeneously in the composites. Many FAC were hollow, and some FAC were filled with Mg alloy matrix. The shapes of most of the Mg 2Si compounds in situ formed were polygons, and their sizes were 10-25 μm. The AZ91-microballoon composites display a typical behavior of brittle foam material in the compression test. There are three main failure modes according to the fractography study: microballoon cracking, debonding of the interface between FAC microballoon and matrix and debonding of the interface between inner matrix and FAC shell. Among these modes, the microballoon cracking is the primary fracture mechanism. © 2012 Elsevier B.V. All rights reserved.