Kai-bo Nie

Effect of Precipitated Phases on Corrosion of Mg95.8Gd3Zn1Zr0.2 Alloy with Long-Period Stacking Ordered Structure

Abstract The microstructure of the precipitated phases of Mg95.8Gd3Zn1Zr0.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast (F), solid-solution (T4) and aging-treated (T6) alloys in 1% NaCl solution are studied. The hydrogen evolution and electrochemical measurements display that the as-cast Mg95.8Gd3Zn1Zr0.2 alloy with the continuous network eutectic phase exhibits the greatest corrosion resistance, while T6 sample with some needle-like phases and the particle phases is the worst among the three alloys. It is proposed to be mainly related to the amount, composition, microstructure and distribution of the precipitated phases.

High-strength Mg95Y3Zn1Ni1 alloy with LPSO structure processed by hot rolling

ABSTRACT Microstructures and mechanical properties of Mg95Y3Zn1Ni1 alloy containing long period stacking ordered (LPSO) phase processed by hot rolling were systematically investigated in the present work. The results showed that the as-cast alloy was mainly composed of α-Mg and network 18 R LPSO phase. The thermal stability of 18 R LPSO phase in the as-cast alloys decreased with the decrease of Ni content. After solution treatment at 773 K for 40 h, network 18 R phase at grain boundary dissolved, while fine lamellar phase identified as 14H LPSO precipitated in the interior of grains. When the solid-solution alloy was hot rolled at 723 K with six passes and thickness reduction of 62%, some LPSO phases broke down and kinking of varying degrees occurred in LPSO phase. Meanwhile, the as-rolled α-Mg and LPSO phase redistributed aligned along the rolling orientation. The alloy exhibited excellent mechanical properties: yield strength of 282 MPa, ultimate tensile strength of 383 MPa, and elongation to failure of 16% at ambient temperature along the rolling orientation. The remarkable improvement of strength was ascribed to the refined microstructure induced by the deformation kinking and the crush of LPSO phase.

Microstructure, mechanical and bio-corrosion properties of Mg–Zn–Zr alloys with minor Ca addition

In this research, effect of minor alloying element Ca on microstructure, mechanical and bio-corrosion properties of as-cast Mg–3Zn–0.3Zr–xCa (x = 0, 0.3, 0.6, 0.9) alloys were investigated for biomedical application. The result showed that Ca played a dual role in mechanical properties and corrosion resistance. With minor Ca addition, the microstructure of the alloy is significantly refined and more uniform. The elongation, tensile strength and corrosion resistance of the studied alloys increases and then decreases with the increase of Ca content. With increasing the Ca content to 0.6 wt-%, the new strip phase of Ca2Mg6Zn3 can be found, and gives the best strength and corrosion resistance. It was thought that the alteration of the second phase and the microstructure affect the mechanical and bio-corrosion properties.

Hot deformation behaviour of as-extruded micrometre SiCp reinforced AZ91 composite

Abstract The 10 μm 10 vol.-% SiCp/AZ91 composite was fabricated by stir casting. After processing by forging and subsequent extrusion, the composite with 1∼2 μm grain size was obtained. Then the hot deformation behaviour of as-extruded composite was investigated at elevated temperatures (543–673 K). Results show that the existence of micrometre SiCp has obvious effect on stimulating dynamic recrystallization (DRX) nucleation and inhibiting the growth of DRXed grains. Both the flow stress and work hardening of as-extruded composite is lower than that of as-cast AZ91 alloy and composite, which means that the grain refinement strengthening mechanism is not fit for elevated temperatures, and the reasons were analysed. The calculated activation energy Q (∼90 KJ mol− 1) of as-extruded composite is very close to the grain boundary diffusion activation energy (∼92 KJ mol− 1) for Mg. Calculation analysis gives n = 5, which illustrates that the climb of dislocation is the main controlling mechanism of the as-extruded composite during hot deformation.

Microstructure characterization and indentation hardness testing behavior of Mg-8Sn-xAl-1Zn alloys

The influence of Al content on microstructure characterization and indentation hardness testing behavior of Mg-8Sn-xAl(x=1 wt%, 2 wt%, 3 wt%)-1Zn alloys was investigated by optical microscope, Pandat software, X-ray diffraction, scanning electron microscope, differential scanning calorimetry and a microhardness testing equipment. The results can be summarized as follows: when the Al content is 1 wt%, the alloy is composed of α-Mg and Mg2Sn phases; while the new phase of Mgx(AlZn)1-x can be observed and the morphology of Mg2Sn phase transfers from the semi-continuous network to the dispersed particles with further addition of Al content to 2 wt% and 3 wt%. The dendrite arm spacing (DAS) deceases firstly and then slightly increases with the increase of Al content. The micro-hardness of Mg-8Sn-xAl(x=1 wt%, 2 wt%, 3 wt%)-1Zn also increases with increasing of Al content. Moreover, the indentation size effect (ISE) in Vickers hardness for Mg-8Sn-1Al-1Zn alloy was observed with the applied test load ranging from 0.490 to 4.903 N.

The effect of high Al content on the microstructure and mechanical properties of Mg-xAl alloys processed by equal channel angular pressing

Abstract In this work, Mg-xAl alloys with an Al content ranging from 10 to 20 wt.% were subjected to equal channel angular pressing (ECAP). The effects of the high Al content on the microstructure and mechanical properties of the alloy before and after ECAP were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis and tensile testing. The results demonstrated that as the amount of Al in the as-cast Mg-xAl alloys increased, the grain size of the as-cast Mg-xAl alloys decreased, whereas the amount of the Mg17Al12 phase with network structure increased. After ECAP, the network β-Mg17Al12 phase was significantly broken into fine pieces. The fine β-Mg17Al12 granules were precipitated from the α-Mg matrix. The broken β-Mg17Al12 phase in the Mg-15Al alloy exhibited a relatively homogeneous distribution. As the Al content increased, the grain size in the α-Mg-rich area decreased. However, the β-Mg17Al12 size in the α+β two-phase area of the ECAPed Mg-15Al alloy was the smallest among the three alloys. The yield strength of the Mg-xAl alloys increased, whereas the elongation to fracture significantly decreased.

Microstructures and biocorrosion properties of biodegradable Mg–Zn–Y–Ca–xZr alloys

Abstract The influence of Zr microalloying on the microstructures and corrosion resistance of as-cast Mg-3.0Zn-0.6Y-0.3Ca (wt.%) alloy were investigated by means of optical microscopy, X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, immersion testing and electrochemical measurements. The results indicated that Zr induced the formation of a strip-like eutectic phase at the grain boundaries, and discouraged the formation of isolated particles. With the Zr addition, the microstructure was refined and the corrosion resistance was enhanced. The alloy with a Zr content of 0.5 wt.% has an optimal corrosion resistance, which can be attributed to the fine and continuously distributed strip-like I-phase and fine grain structure.