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In this study, Mg-9Al-1Si-1SiC (wt%) composites were processed by multi-pass equal-channel angular pressing (ECAP) at various temperatures, and their microstructure evolution and strengthening mechanism were explored. Results showed that the as-cast microstructure was composed of an α-Mg matrix, discontinuous Mg17Al12 phase, and Chinese script-shaped Mg2Si phase. After solution treatment, almost all of the Mg17Al12 phases were dissolved into the matrix, whereas the Mg2Si phases were not. The subsequent multi-pass ECAP at different temperatures promoted the dynamic recrystallization and uniform distribution of the Mg17Al12 precipitates when compared with the multipass ECAP at a constant temperature. A large number of precipitates can effectively improve the nucleation ratio of recrystallization through a particle-stimulated nucleation mechanism. In addition, the SiC nanoparticles were mainly distributed at grain boundaries, which effectively prevented dislocation movement. The excellent comprehensive mechanical properties can be attributed to grain boundary strengthening and Orowan strengthening. [ABSTRACT FROM AUTHOR]

Ideal biodegradable materials exhibit suitable degradation rates and sufficient mechanical properties for their specific application. With these parameters in mind, Zn–Mg/Mg–Zn–hydroxyapatite (HAp) laminated composites were designed and fabricated by spark plasma sintering. This paper describes the structure, mechanical properties, in vitro corrosion resistance, and cytotoxicity of the Zn–Mg/Mg–Zn–HAp laminated composites. The compressive strength and elastic moduli of the laminated composites matched that of cortical bone and could effectively reduce the stress shielding effect as an implant with good biomechanical compatibility. Analysis of the fracture path and morphology after fracture toughness tests indicated that the Zn–Mg/Mg–Zn–HAp laminated composites exhibited significant capacity to prevent crack propagation, improving the fracture toughness. In vitro degradation experiments showed that the design of the laminated structure can provide a gradient degradation rate for the material. Furthermore, the laminated composites exhibited excellent biocompatibility and are promising candidates for orthopedic implants. [ABSTRACT FROM AUTHOR]

An icosahedral quasicrystal phase (I-phase)-containing Mg-8Sn-6Zn-2(wt.%)Al (TZA862) alloy was subjected to ECAP and subsequent double aging. Thereafter, the age-hardening microstructure and tensile properties of the as-ECAPed TZA862 alloy were investigated. The results indicated that the grain size, fraction and orientation of the precipitates as well as the texture were affected by the double-aging treatment, which contributed to the enhanced hardness and tensile strength. The hardening of the aged alloy was mainly ascribed to the nucleation of the precipitates on grain boundaries and the strengthening was mainly related to the Orowan mechanism. [ABSTRACT FROM AUTHOR]

A “RE-free” and I-phase-containing Mg–8Sn-based alloy system was developed and successfully fabricated through the equal channel angular pressing (ECAP) process. The influence of the Zn/Al mass ratio on the microstructures and mechanical properties of the as-ECAPed Mg–8Sn–(5,6,7)Zn–2(wt%)Al alloys was investigated using an optical microscope, an X-ray diffractometer, a scanning electron microscope, a transmission electron microscope, and a universal testing machine. Grain size, dynamic recrystallization behavior, and texture were found to be greatly affected by the Zn/Al mass ratio. Furthermore, the ultimate tensile strength (250 MPa) and elongation (14.5%) of the alloy with a Zn/Al mass ratio of 3 were considerably increased compared to those of the as-ECAPed alloys with Zn/Al ratios of 2.5 and 3.5 (ultimate tensile strength and elongation of 215 MPa and 13% and 184 MPa and 10%, respectively). This significant enhancement was attributed to extensive grain boundary strengthening, precipitation strengthening, and higher work hardening capacity as well as texture randomization. The strength and ductility of the as-ECAPed alloys are also discussed in terms of the I-phase and Mg2Sn formation. [ABSTRACT FROM AUTHOR]

Mg-8Sn-1Al-1Zn- xNi ( x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction) alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope, energy dispersive X-ray spectroscope, X-ray diffraction and a standard universal testing machine. The results show that the microstructure of Ni-containing alloys consist of α-Mg, MgSn, β-Mg-Ni-Al and γ-AlNi phases. No β-Mg-Ni-Al phase was observed in TAZ811-2.0Ni alloy due to its 1:1 atomic ratio of Ni/Al. The addition of Ni refines the α-Mg dendrites and suppresses the formation of coarse MgSn phase. The tensile properties results show that the TAZ811-0.5Ni alloy presented the best mechanical properties, which is due to the rod-like β-Mg-Ni-Al phase, refined α-Mg dendrites and MgSn phase, as well as γ-AlNi phase. The tensile fracture mechanism transits from cleavage to quasi-cleavage fracture with the increasing Ni addition. [ABSTRACT FROM AUTHOR]

The microstructural evolution and mechanical properties of high speed indirect-extruded Mg-5%Sn-(1, 2, 4) Zn (mass fraction, %) alloys were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and a static tension tester. All the studied alloys can be extruded successfully at a high speed of 10 m/min. The grain size, area fraction of particles and tensile properties are found to be greatly affected by the extrusion speed and Zn content, resulting in tensile properties showing lower strength and ductility as the extrusion speed increases and Zn content decreases. The dependence of grain size and tensile properties on the second phase particles is also discussed. [ABSTRACT FROM AUTHOR]

Indirect extrusion of Mg-10%Sn (mass fraction) alloys was performed at three different working temperatures. The effect of working temperature on the microstructure, texture and tensile properties of the extruded alloys was investigated by optical microscope (OM), scanning electronic microscope (SEM), X-ray diffraction (XRD) and a standard universal testing machine. Grain size, area fraction of second phase particles and texture of the alloys are found to be significantly influenced by working temperature. The grain size refinement is greatly dependent on processing conditions with the low working temperature being the most effective. While the high working temperature results in a coarser grain size and a stronger fiber texture and the reason for this phenomenon was examined in terms of second phase particle, grain type and dynamic recrystallization mechanism. Tested in the different conditions, the tensile strengths of the Mg-10Sn alloys extruded at the high working temperature are remarkably better than those of the other studied alloys. This significant improvement in tensile properties is mainly due to the particle strengthening and texture strengthening resulted from the more and finer primary dispersed particles and stronger texture, respectively. [ABSTRACT FROM AUTHOR]

The medium and warm deformation behaviors of an indirect-extruded Mg-8Sn-1Al-1Zn alloy were investigated by compression tests at temperatures between 298 and 523 K and strain rates of 0.001-10 s. It was found that the twinning-slip transition temperature was strain rate dependent, and all the true stress-true strain curves could be divided into two groups: concave and convex curves. Associated microstructural investigations indicated that the dynamic recrystallization (DRX) behavior of the alloy varied with deformation conditions. At high strain rate and low temperature, dynamically recrystallized grains preferentially nucleated and developed in the twinned regions, indicating that twinning-induced DRX was dominant. While, at low strain rate, DRX developed extensively at grain boundaries and twins, and the process of twinning contributed to both oriented nucleation and selective growth. For the studied alloy, cracks mainly initiated from the shear band and twinning lamellar over the ranges of temperature and strain rate currently applied. [ABSTRACT FROM AUTHOR]