Xiao Shi Hu

Mechanical Properties and Damping Behavior of Magnesium Alloys Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) was applied to commercial pure magnesium alloy, Mg-1wt%Si alloy and Mg-4.2wt%Zn-0.7wt%Y alloy. With increasing ECAP passes, both tensile strength and ductility of the alloys are increased, which are mainly resulted from the grain refinement. At the same time, for the Mg-Zn-Y alloy with inherent low damping capacity, damping capacity is increased after ECAP passes, however, the damping capacity is still low even after 6-pass ECAP. While for the commercial pure magnesium and Mg-Si alloy with inherent high damping capacity, although the damping capacity is decreased obviously after ECAP, Q-1 is still greater than 0.01. The damping capacity after ECAP processing is mainly influenced by grain size and deformation microstructure. ECAP paves a way for the development of magnesium alloys with high strength and high ductility combined with high damping capacity.

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.

Microstructure and Mechanical Properties of Extruded Mg-Zn-Ca Alloy

The as-cast Mg - 5.25 wt.% Zn - 0.6 wt.% Ca alloy was extruded at different extrusion temperatures (270, 300, and 330 °C). The extrusion temperature has a significant effect on the grain size, texture and mechanical properties of the Mg-Zn-Ca alloy. Upon extrusion, the as-cast coarse grains underwent pronounced grain refinement and the second phases were broken up and formed stringers in the extrusion direction. With the decreasing extrusion temperature to 270 °C, the grain size of the alloy was refined to about 1.5 μm, basal texture became stronger, which led to the higher tensile strength and moderate elongation to failure.

Microstructure and Properties of Pure Mg/ZK60 Laminate Processed by Accumulative Roll Bonding

Commercial pure magnesium with excellent damping capacity and ZK60 magnesium alloy with high strength were accumulative roll bonded (ARBed) at 300oC up to 3 cycles to fabricate Mg laminate consisting of alternating layers of pure Mg and ZK60. Microstructure, tensile properties and damping capacity of the sheets were analyzed. The research suggests that Mg sheet having both high strength and excellent damping capacity can be developed by accumulative roll bonding of pure Mg and ZK60 Mg alloy.

The Fracture Mechanism of As-Cast and Extruded SiCp/AZ91 Composites Fabricated by Stir Casting

The fracture mechanisms of SiCp/AZ91 composites were investigated by scanning electron microscopy (SEM). For the as-cast composites, the decohesion at SiCp/matrix interface is the main fracture mechanism because of the high stress concentration resulting from the segregation of particles in grain boundaries formed during solidification process. But for the extruded composites, the main fracture mechanism is the particle crack or ductile rupture of the matrix between the particles. So the fracture mechanism of SiCp/AZ91 composites is altered by extrusion because the segregation of particles and defects in the grain boundaries are largely eliminated by extrusion.

Effect of Deformation on the Damping Capacity of Magnesium Alloys

Equal channel angular extrusion (ECAE) was applied to an as-cast AZ91D magnesium alloy. The strain amplitude dependence and temperature dependence of damping capacities of the as-cast and ECAE processed AZ91D alloys were investigated by dynamic mechanical analyzer (DMA). Microstructures of AZ91D alloys after ECAE were observed by optical microscopy (OM). In higher strain region, the damping value of 4-pass ECAE deformed AZ91D alloy was the highest among all the AZ91D alloys under different conditions. The damping peaks of ECAE deformed AZ91D alloys detected during heating from room temperature to 400°C were considered to be related to the migration of grain boundaries and the movement of dislocations during recrystallization.

Application of G-L Dislocation Model in Low Frequency Damping Capacities of AZ91D and SiCw/AZ91D Composites

The low frequency damping capacities of commercial cast AZ91D, squeeze cast AZ91D alloy and SiCw/AZ91D composite were studied using dynamic mechanical analyzer (DMA). The obtained strain amplitude dependent damping could be divided into two regions. In the region of small strain amplitude, the damping capacity was independent of the amplitude. While at high strain region, the damping capacity increased rapidly with increasing of strain amplitude. The G-L dislocation model was used to explain the damping capacity, and the differences of the distance between the weak and strong pinning points were discussed. The microstructures of the alloys and composites were observed and coincided with the analysis results according to G-L dislocation model.

Low Frequency Damping Behaviors of Magnesium Alloys

The effect of different alloying elements including Ni, Si and Al and various mass contents of these elements on the low frequency damping behaviors of magnesium alloys were investigated. The measurements of strain dependent and temperature dependent damping capacities of these magnesium alloys were carried out using dynamic mechanical analyzer (DMA), and the very different damping behaviors of these magnesium alloys were found. The hypoeutectic magnesium alloys with low solubility alloying elements such as Si and Ni shown extremely high damping capacities. But the Mg-Al alloys exhibited very low damping values. The tensile properties of these magnesium alloys were also illustrated in this study. It was found that hypoeutectic Mg-1.0%Si alloy possess the excellent overall properties with high damping capacity, relatively high tensile properties and good corrosion resistant ability.