M.Y. Zheng

Ageing behavior of extruded Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy containing LPSO phase and γ′ precipitates

The effect of long period stacking ordered (LPSO) phase and γ′ precipitates on the ageing behavior and mechanical properties of the extruded Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt.%) alloy was investigated. The results show that more β′ phases precipitate during ageing treatment in the LPSO phase containing alloy so that the LPSO phase containing alloy exhibits a higher age-hardening response than the γ′ precipitates containing alloy. The precipitation strengthening induced by β′ precipitates is the greatest contributor to the strength of the peak-aged LPSO-containing alloys. Higher strength is achieved in γ′ precipitates containing alloy due to the more effective strengthening induced by dense nanoscale γ′ precipitates than LPSO phases as well as the higher volume fraction of coarse unrecrystallized grains with strong basal texture. The extruded alloy containing γ′ precipitates after T5 peak-ageing treatment shows ultra-high tensile yield strength of 462 MPa, high ultimate tensile strength of 520 MPa, and superior elongation to failure of 10.6%.

Texture Evolution of the Mg/Al Laminated Composite by Accumulative Roll Bonding at Ambient Temperature

Abstract The Mg/Al laminated composites were prepared by the accumulative roll bonding (ARB) at ambient temperature using the commercial pure magnesium and pure Al sheets as starting materials. Microstructure of both Mg and Al layer were refined during ARB processing. Neutron diffraction was employed to investigate the texture evolution of this kind of laminated composite. Both the Mg and Al layer of the primary sandwich exhibited dominant shear texture. During the following accumulative roll bonding, the texture of Mg layer transformed to typical rolling texture while the Al layer showed a combined texture type including evident β fiber and the Rotate Cube component.

Mechanical spectroscopy of Al-Mg alloys

The internal friction of deformed, annealed, and quenched Al-Mg alloys with Mg contents of 0–12 wt % has been studied as a function of temperature. The measurements have been performed in the range of 25–580°C at 0.3–30 Hz using a DMA Q800 TA Instruments dynamic mechanical analyzer at the maximum amplitude of deformation ɛ0 = 5 × 10−5. In annealed alloys with Mg contents up to 5 %, a relaxation IF peak with activation parameters (activation energy H ≈ 1.7–2.1 eV) has been detected. In alloys with 8–12% Mg, this relaxation peak is absent and, at a lower temperature, another IF peak appears (with an activation energy H of about 1 eV), which is interpreted as the Zener peak in terms of the combination of activation parameters. The article discusses the nature of these peaks and the influence of alloying on the relaxation mechanisms. In cold-worked alloys, an IF pseudo-peak takes place, which is related to the recrystallization of samples, and its temperature position in the alloys that contain more than 5% Mg depends not only on the degree of deformation, but also on the dissolution temperature of the β phase.

Texture development of ARB processed Mg/Al multilayers

Our work deals with accumulative roll bonding (ARB) of pure Mg sheet (0.9mm thickness) and of Al5052 sheet (0.5mm). A stacking of Al-Mg-Al was firstly rolled to 50% reduction at 400°C and secondly ARB has been processed up to 3 cycles. In such multilayers as well as highly mixed composites of two-phased system texture development, phase reactions and strain accumulation are of basic interest, which needs a combination of different experimental methods for characterization. The present paper deals with the global texture evolution measured by thermal neutrons to average always over the whole sample thickness, SEM and optical microscopy indicates the macroscopic development of Mg and Al layers. The initial materials show typical and strong basal plane texture of hexagonal Mg (17.9mrd) and a recrystallization texture of cubic Al (8.5mrd). Co-deformation of Al/Mg/Al leads to strong decrease of both textures, whereas Mg has always a much stronger texture than Al5052. ARB processing produces only weak Al-textures. After sandwich-rolling and 1 cycle ARB rotated cube is observed in Al5052, which does not exist after 2 and 3 cycles of ARB.

Development of Ultra-High Strength and Ductile Mg–Gd–Y–Zn–Zr Alloys by Extrusion with Forced Air Cooling

Magnesium alloys containing heavy rare earth metals (HRE) have been attracting wide attention due to their remarkable age-hardening response. Extrusion of Mg-HRE alloys generally requires high ram force, leading to heat generation during the extrusion. In this study, by simply utilizing forced air cooling, high strength Mg–8.2Gd–3.8Y–1Zn–0.4Zr (wt%) alloy with good ductility was successfully developed via tailoring the microstructure. The dynamic recrystallization (DRX) ratio, grain size and texture can be controlled by cooling during the extrusion process, that is, the forced air cooling reduces the extrusion temperature and brings about rapid cooling of the extrudate after extrusion. Consequently, the alloy extruded with forced air cooling exhibits high tensile yield strength of 378 MPa, ultimate tensile strength of 436 MPa and high elongation to failure of 12.5% due to a bimodal microstructure consisting of finer DRXed grains with relatively random orientations and coarse unrecrystallized grains with a strong basal fiber texture.

Improvement of Strength and Ductility of Mg‐Zn‐Ca‐Mn Alloy by Equal Channel Angular Pressing

An ultrafine-grained (UFG) Mg-5.25 wt.% Zn-0.6 wt.% Ca-0.3 wt.% Mn alloy was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250 and 300 °C, respectively. ECAP resulted in a remarkable grain refinement. After ECAP processing at 250°C, basal planes are oriented both parallel and inclined about 45° to the extrusion direction, while most the basal planes are oriented parallel to the extrusion direction after ECAP processing at 300 °C. Both yield strength and elongation were increased after ECAP processing. The yield strength was higher in the ECAPed alloy processed at 300 °C with larger grain size, indicating that the texture strengthening effect was dominant over the strengthening from grain refinement in the ECAPed alloy. The grain refinement may lead to dislocation slip on non-basal plane and grain boundary sliding, which improved the ductility of the ECAPed Mg-Zn-Ca-Mn alloy.