Hucheng Pan

High conductivity and high strength Mg–Zn–Cu alloy

Abstract In the present work, electrical conductivity (EC) and Vickers hardness of Mg–Zn–xCu (x = 0, 0·5, 1·0 and 1·5) alloys in as cast, as solution and aged states have been investigated. The result shows that the EC of both as cast and as solution samples increases with Cu content, and Cu addition would have remarkably enhanced effect on EC and age hardening response during subsequent aging treatment. The 1·0Cu alloy aged at 160°C for 16 h after solution treatment had the optimal combined properties of high microhardness (94 HV) and high EC value (19·1, 106 S m−1), noting that the EC of pure Mg is 22·8 (106 S m−1). It is believed that the accelerated precipitation process for Cu containing alloy is attributed to the favourable interactions between Zn, Cu and vacancies. The microstructure associated with the improvement of EC and microhardness for Cu containing alloy is also discussed in detail.

Preparation and characterization of Mg alloy rods with gradient microstructure by torsion deformation

Extruded AZ31 Mg alloy rods were subject to free-end torsion deformation at room temperature. The microstructure features of the torsion deformed samples were characterized using electron backscatter diffraction technique. Mg rods with gradient microstructure can be fabricated by torsion deformation. Inhomogeneous distribution of microstructure along the radial direction of the twisted rods is attributed to the linearly increasing strain accumulation and strain rate from core to surface. With increasing equivalent strain, both the amount of {10-12} twins and dislocation density increase and the c-axes of texture tend to rotate towards torsion axis. Although both dislocation slips and {10-12} twinning can be activated during torsion, dislocation slips are considered as the dominated deformation mechanism and responsible for the change of macro-texture for present torsion deformation. {10-12} twins and dislocations in the twisted samples can generate refinement hardening and dislocation hardening, respectively, to increase the hardness value.

Microstructure and mechanical properties of asextruded Mg–xAl–5Sn–0·3Mn alloys (x = 1, 3, 6 and 9)

Abstract Properties of Mg–xAl–5Sn–0·3Mn alloys (x = 1, 3, 6 and 9) prepared by hot extrusion are reported. The orientation relationship between Mg2Sn precipitate and Mg matrix in Mg–9Al–5Sn–0·3Mn alloy was determined. The yield strength of the as extruded alloys initially decreased with increasing Al content, then increased for Al contents >6 wt-%. These changes are interpreted in terms of the effect of texture, grain size and second phase on the yield strength of the alloys.

Thermal and electrical conductivity of Mg–Zn–Al alloys

Abstract In the present work, thermal and electrical conductivity measurement was conducted on the cast Mg–Zn–Al alloys (ZA alloys) in the wide composition range (1–6 wt-%Zn, 1–10 wt-%Al). For alloys with the same content of Zn, the thermal/electrical conductivity of ZA alloys decreased exponentially with Al composition without exception. For alloys with same Al content, variation of thermal/electrical conductivity showed a similar trend for most of the alloys except the case for 6 wt-%Al, which followed ZA26>ZA36>ZA16>ZA56>ZA66. The microstructures of the selected alloy systems were investigated in detail, and the mechanism of thermal/electrical conductivity variation was thus proposed. The phase transformation with composition and the different effects of Zn and Al on the thermal/electrical conductivity of Mg alloys were believed as two controlling factors.

Improving Tensile and Compressive Properties of an Extruded AZ91 Rod by the Combined Use of Torsion Deformation and Aging Treatment

In this study, AZ91 magnesium alloy rods were used to investigate the effects of torsion deformation on microstructure and subsequent aging behavior. Extruded AZ91 rod has a uniform microstructure and typical fiber texture. Torsion deformation can generate a gradient microstructure on the cross-section of the rod. After torsion, from the center to the edge in the cross-section of the rod, both stored dislocations and area fraction of {10-12} twins gradually increase, and the basal pole of the texture tends to rotate in the ED direction. Direct aging usually generates coarse discontinuous precipitates and fine continuous precipitates simultaneously. Both twin structures and dislocations via torsion deformation can be effective microstructures for the nucleation of continuous precipitates during subsequent aging. Thus, aging after torsion can promote continuous precipitation and generate gradient precipitation characteristics. Both aging treatment and torsion deformation can reduce yield asymmetry, and torsion deformation enhances the aging hardening effect by promoting continuous precipitation. Therefore, combined use of torsion deformation and aging treatment can effectively enhance the yield strength and almost eliminate the yield asymmetry of the present extruded AZ91 rod. Finally, the relevant mechanisms are discussed.

Tension-compression asymmetry of a rolled Mg-Y-Nd alloy

In this work, tension and compression deformation behaviors of rolled and aged Mg-Y-Nd alloys were investigated. The microstructure evolution and plastic deformation mechanism during tension and compression were analyzed by combined use of electron backscatter diffraction and a visco-plastic self-consistent crystal plasticity model. The results show that both rolled and aged Mg-Y-Nd sheets show an extremely low yield asymmetry. Elimination of yield asymmetry can be ascribed to the tilted basal texture and suppression of {10-12} twinning. The rolled sheet has almost no yield asymmetry, however exhibits a remarkable strain-hardening behavior asymmetry. Compressed sample shows lower initial strain hardening rate and keeps higher strain hardening rate at the later stage compared with tension. The strain-hardening asymmetry can be aggravated by aging at 280 C. It is considered the limited amount of twins in compression plays the critical role in the strain hardening asymmetry. Finally, the relevant mechanism was analyzed and discussed.

Formation of profuse dislocations in deformed calcium-containing magnesium alloys

Abstract We report that pyramidal slipping could be more easily activated in textured Mg–Ca alloys with increasing Ca contents dissolved in α-Mg matrix under tensile deformation, and it is proposed that the decreased stacking fault energy plays the critical rule. In contrast, only twins and basal dislocations are observed in the compressed samples. The results would provide insight into understanding of the deformation mechanism and designing more ductile Mg alloys.

Microstructure, mechanical and bio-corrosion properties of as-extruded Mg–Sn–Ca alloys

Abstract The as-extruded Mg–Sn–Ca alloys were prepared and investigated for orthopedic applications via using optical microscopy, scanning electron microscopy, X-ray diffraction, as well as tensile, immersion and electrochemical tests. The results showed that, with the addition of 1% Sn and the Ca content of 0.2%–0.5%, the microstructure of the as-extruded Mg–Sn–Ca alloys became homogenous, which led to increased mechanical properties and improved corrosion resistance. Further increase of Ca content up to 1.5% improved the strength, but deteriorated the ductility and corrosion resistance. For the alloy containing 0.5% Ca, when the Sn content increased from 1% to 3%, the ultimate tensile strength increased with a decreased corrosion resistance, and the lowest yield strength and ductility appeared with the Sn content of 2%. These behaviors were determined by Sn/Ca mass ratio. The analyses showed that as-extruded Mg–1Sn–0.5Ca alloy was promising as a biodegradable orthopedic implant.

Self-Assembly of Two Unit Cells into a Nanodomain Structure Containing Five-Fold Symmetry

Five-fold symmetry was forbidden for the periodic crystals until the discovery of the Al-Mn icosahedral quasicrystal. We report a kind of precipitated rod-shaped nanophase containing five-fold symmetry but not belonging to any crystals or quasicrystals discovered so far. These metastable nanodomain phases, which precipitated in Mg-6Zn alloy during isothermal aging at 200 °C, contain two separate unit cells in the 2D plane perpendicular to the five-fold axis but with periodic atom arrangement along the five-fold axis, that is, 72° rhombus structure and 72° equilateral hexagon structure. The self-assembly of two unit cells under some geometrical constraints into a nanodomain contains the 2D five-fold, C14, and C15 structures. This finding confirms the existence of solid matters in a special structure between the crystals and quasicrystals, and it is expected to provide a way to understand the atomic arrangement and stacking behavior in condensed matters.

Effect of Cu/Zn on microstructure and mechanical properties of extruded Mg–Sn alloys

In this paper, the effect of Cu and Zn addition on mechanical properties of indirectly extruded Mg–2Sn alloy was investigated. Mg–2Sn–0.5Cu alloy exhibits a moderate yield strength (YS) of 225 MPa and an ultimate strength of 260 MPa, which are much higher than those of the binary Mg–2Sn alloy, and the elongation (EL) evolves as ∼15.5%. Mechanical properties of the Mg–2Sn–0.5Cu alloy are deteriorated with more 3 wt-% Zn addition, and YS and EL are reduced as 160 MPa and ∼10%. The detailed mechanism is discussed according to the work-hardening rate and strengthening effect related to the grain sizes, second phases and macro-textures. Grain refinement and proper texture are believed to play a critical role in both strength and ductility optimisation.