MECHANICAL PROPERTY AND FRACTURE-BEHAVIOR OF SQUEEZE-CAST MG MATRIX COMPOSITES

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-cast ing technique, with variations in the reinforcement material and appli ed pressure. Microstructural and fractographic observations, along wit h in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process; Two of them are rein forced with two different short fibers and the other is a whisker-rein forced composite. From the in situ fracture observation of Kaowool-rei nforced composites, the effect of the applied pressure on mechanical p roperties is explained using a competing mechanism: the detrimental ef fects of fiber breakage act to Impair the beneficial effects of the gr ain refinement and improved densification as the applied pressure incr eases. On the other hand, for the composites reinforced with Saffil sh ort fibers, microcracks were initiated mainly at the fiber/matrix inte rfaces at considerably higher stress intensity factor levels, while th e degradation of fibers was not observed even in the case of the highe st applied pressure. This finding indicates that the higher applied pr essure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropria te applied pressure in the short fiber-reinforced composites, their me chanical properties were far below those of conventional Al matrix com posites. In this regard, the Alborex aluminum berate whisker is sugges ted as a replacement for the short fibers used in the present investig ation, to achieve better mechanical properties and fracture toughness.