In-situ quasicrystal-reinforced magnesium matrix composite processed by equal channel angular extrusion (ECAE)

Abstract

Magnesium alloys have a strong potential for applications in structural components because of their low density. Considerable effort is currently being devoted to the development of high performance magnesiumbased materials for aerospace and outer space applications. Apart from conventional alloying practice, there has been a rapid development of particle or fiber reinforced magnesium matrix composites [1, 2]. The use of ceramics as reinforcement in magnesium alloys resulted in significant improvement of strength and stiffness. However, such strength and stiffness benefit is at the expense of a rather poor ductility [1, 2]. Quasicrystals are isotropic and possess quasiperiodic lattice structure [3]. Due to the difficulty of the movement of dislocations in the quasicrystals at room and elevated temperatures, quasicrystals exhibit high hardness and high strength [4]. Therefore, quasicrystals have been successfully used as reinforcements in metal-matrix composites [5–7]. For example, quasicrystal-reinforced aluminum matrix composites with high strength combined with good ductility have been developed by powder-metallurgical method [5, 6] and casting process [7]. Recently, it was reported that a thermal stable icosahedral quaiscrystalline phase (I-phase) with chemical composition of Mg3YZn6 was formed as a coarse eutectic structure in the α-Mg matrix during conventional solidification in Mg-Zn-Y alloy system [8]. The existence of the two-phase (I-phase + α-Mg) region in the Mg-Zn-Y alloy system provides an opportunity to develop quasicrystal-reinforced magnesium matrix composites by thermal processing. Conventional thermomechanical processes, such as hot rolling [9, 10] and extrusion [11], have been employed for the alloy system to separate and distribute the I-phase in the α-Mg matrix, thus in-situ I-phase/magnesium matrix composites with high strength and ductility have been achieved [9–11]. Equal channel angular extrusion (ECAE) is a novel metal forming process to produce severe plastic strains in bulk material without changing the cross-section of the material [12]. This procedure has been recognized as one of the most effective methods in producing bulk ultra-fine grained (UFG) materials with