Overcoming the specific stiffness/ductility trade-off in ZX50/SiC magnesium composites through solute-segregation interface strengthening and deformation-induced recrystallization

The specific stiffness of structural metallic alloys is around 26 MJ·kg −1 and conventional strengthening strategies (alloying and thermomechanical processing) cannot overcome this limitation. It is, however, well established that superior values of specific stiffness can be achieved by reinforcing with stiff ceramic particles. Mg alloys are ideal candidates for this purpose because of their moderate mechanical properties and low density, but the introduction of large volume fractions of ceramic particles always systematically led to the composites with negligible ductility due to the weak particle/matrix interfacial bonding and poor toughness of the interface region. Here, we report a novel Mg-5Zn-0.2Ca/SiC composite with superior specific stiffness (34 MJ·kg −1 ), high strength (> 300 MPa) and ductility (> 7 %). The composite is manufactured through semi-solid stirring, followed by extrusion, a technique can be easily scaled-up for industrial applications. The co-segregation of Zn/Ca atoms along the interface enhances the atomic bonding and delays interface decohesion and microcrack initiation at the particle/matrix interface. Moreover, the activation of 〈 c + a〉 dislocations near the Mg alloy/SiC interface was confirmed, and their subsequent rearrangement into dislocation arrays was found to promote dynamic recrystallization, thus contributing to crack-tip blunting and enhanced damage tolerance. This mechanism improves the toughness and delays crack propagation, allowing the development of strain hardening and improving dramatically the tensile ductility of the composite. The present work provides an efficient approach to improve the interfacial properties and further inspires the development of high-performance metal matrix composites with exceptionally high modulus, strength and ductility.