Dynamic recrystallization behavior of particle reinforced Mg matrix composites fabricated by stir casting

Abstract

► The necklace-type particle distribution caused the necklace DRX. ► DRX extended from the initial intergranular areas to the initial transgranular areas. ► The necklace DRX mechanism was built for Mg matrix composites. The dynamic recrystallization (DRX) of a 10 μm10% SiCp/AZ91 composite during hot compression was studied using optical microscope and transmission electron microscope. In the as-cast composite, SiC particles were segregated along grain boundaries, which was like necklaces along the grain boundaries. Thus, particles aggregated at transgranular areas while particles were almost absent at the grain interiors. During hot compression, particle deformation zones (PDZs) were formed near particles due to the mismatch between SiC particles and Mg matrix. DRX preferentially started near particles due to “particle-stimulated nucleation (PSN)” in PDZs. Therefore, this necklace particle distribution caused initiation of DRX along the pre-existing (initial) grain boundaries. As a result, the initial grain boundaries were entirely covered by new and fine DRX grains, and necklace structure of DRX grains was formed along the grain boundaries. As DRX further proceeded, DRX extended from the intergranular areas of the initial grains to the initial grain interiors. According to the microstructure investigations and analysis, the necklace mechanism for DRX was established for Mg matrix composites with necklace particle distribution.