Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

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Precipitation and Hardening in Magnesium Alloys

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Effect of multimodal microstructure evolution on mechanical properties of Mg–Zn–Y extruded alloy

Effect of Y concentration on the microstructure and mechanical properties of as-cast Mg–Zn–Y–Zr alloys

This work mainly studied the influence of the microstructure and crystallographic texture on the mechanical properties of the as-extruded Mg-Zn-Y-Zr alloys with different Y contents. The samples were machined from thick plates obtained by extrusion and the tensile tests were performed parallel to extrusion and transverse directions, respectively. Microstructure observation firmly indicated that the grain-refining effect of icosahedral quasicrystal phase (I-phase) was superior to that of the cubic W-phase. In addition, the tensile results indicated that I-phase could effectively improve the strength (yield strength and ultimate tensile strength) of alloys. However, strengthening effect of W-phase was lower. With the quantity of W-phase increasing, the strength of alloys was degraded. It also showed that the alloys were mechanically anisotropic, i.e. the longitudinal strength was higher than that of the transverse direction. However, the ductility of the transverse direction was superior. With the increase of Mg-Zn-Y phases, the anisotropy of the ultimate tensile strength (UTS) between the longitudinal and transverse directions increased remarkably. SEM fracture observations showed that the fractures of the TD samples were characterized by the typical "woody fracture", with a large amount of cracked Mg-Zn-Y particles (I-phase and W-phase) distributed at the bottom of dimples. With Y content increasing, the average spacing of the zonal distributed Ma-Zn-Y particles on the fracture surface became narrow, which influenced the transverse mechanical properties greatly. (c) 2006 Elsevier B.V. All rights reserved.

Daokui Xu

Papers

Effect of Y concentration on the microstructure and mechanical properties of as-cast Mg–Zn–Y–Zr alloys

Effect of microstructure and texture on the mechanical properties of the as-extruded Mg–Zn–Y–Zr alloys

The influence of element Y on the mechanical properties of the as-extruded Mg-Zn-Y-Zr alloys

Effect of W-phase on the mechanical properties of as-cast Mg–Zn–Y–Zr alloys

Effect of long-period stacking ordered phase on microstructure, mechanical property and corrosion resistance of Mg alloys: A review