Wen-bin Fang

Microstructures and mechanical properties of pure magnesium bars by high ratio extrusion and its subsequent annealing treatment

Abstract Pure magnesium bars were prepared by two-pass cumulative high ratio extrusion with as-cast Mg as the original material and then the final as-extruded bars were annealed. The effect of extrusion deformation and annealing treatment on the microstructure, mechanical properties and fracture behaviour of the Mg were investigated by optical microscopy (OM), mechanical properties test and scanning electron microscopy (SEM), respectively. The results show that the grain size is obviously refined by the effect of dynamic recrystallization during the extrusion deformation. Thus the room-temperature mechanical properties and fracture behaviour of the material were significantly improved. After the first extrusion, the coarse as-cast grain size was reduced to 35 μm, and the yield strength (YS), ultimate tensile strength (UTS) and elongation of the bar achieved 84 MPa, 189 MPa, and 12%, respectively. After the further extrusion, the YS of as-extruded bar was over 120 MPa; however, the elongation decreased due to work hardening. Finally the grain size of the as-extruded bar was 9-10 μm after annealing treatment, and its YS, UTS and elongation of the bar achieved 124 MPa, 199 MPa, and 10.7%, respectively. The microstructures and mechanical performance of the material were enhanced obviously.

Corrosion behavior of extrusion-drawn pure Mg wire immersed in simulated body fluid

The corrosion behaviors of extrusion-drawn pure magnesium wire soaked in simulated body fluid (SBF) and 0.9% NaCl solution were studied. The corrosion law of the pure magnesium wire immersed in SBF was investigated by measuring the average corrosion rate and the pH values of the solution after corrosion. It is found that the corrosion mechanism of the pure magnesium wire was pitting after the observation of corrupted surface morphology by scanning electron microscopy (SEM). Moreover, the corrosion law of extrusion-drawing pure magnesium wire in 0.9% NaCl solution implied that the smaller the grain size of the wire is, the better the corrosion resistance exhibits.

Characterization of Ti-50%Al composite powder synthesized by high energy ball milling

The Ti-50%Al (molar fraction) composite powder was synthesized by high energy ball milling (HEBM). The characteristics of the composite particles, including surface morphology, structure and components, were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The mechanochemical reaction between Ti and Al gradually took place through intermediate stages during milling, and resulted in the formation of disordered Ti/Al phases. Dissolution of Al in Ti (after 9 h milling), nanocrystalline Ti/Al solid solution and high density of dislocations were caused by HEBM. The element distribution of the mechanically alloyed Ti-50%Al composite powder was close to the initial composition, but the distribution was inhomogeneous.

Structure and morphology of Ti-Al composite powders treated by mechanical alloying

Abstract The evolution in microstructure and composition of the milled Ti-Al composite powder with different milling time were investigated. It shows that with the milling time increasing, the initial powder underwent a successive change in its morphology from a flattened shape (2 h) to a fine, equiaxed and uniform one (above 6 h). The milled Ti-Al composite powder was nanocrystalline with the average crystallite size of about 17 nm after milling for 8 h. The evolution mechanism of Ti-Al composite powder was elucidated. The Ti(Al) solid solution is formed through a gradual and progressive solution of Al into Ti lattice. By differential thermal analysis on the ignition temperature of the reaction between Ti and Al as a function of milling time, it indicates that mechanical milling of the powders significantly lowered the ignition temperature of the reaction by refining its Ti-Al composite structure.

Characterization of TiAl-based alloy with high-content Nb by powder metallurgy

Abstract Powders with nominal composition of Ti-45Al-10Nb (mole fraction, %) were prepared by mechanical ball milling and were then consolidated by hot-pressed sintering in vacuum atmosphere. The microstructures of 12 h-milling composite powders and sintered bulk materials were characterized by OM, XRD, SEM and EDX. The results showed that the composite powders were completely homogeneous, and fine-grained Ti/Al/Nb composite powders were made. The microstructure of the consolidated alloy was composed of fine equiaxed grains with large pure Nb particles. And the results also indicated that the compressive strength and ductility of the sintered TiAl-based bulk material at RT could be improved effectively by adding 10% Nb element. The yield strength (σ 0.2 ) and fracture strength (σ b ) of the alloy were 842 MPa and 1314 MPa, respectively, and the compressive ductility (δp) was 12.4%.

Preparation of bulk ultrafine-grained Mg-3Al-Zn alloys by consolidation of ball milling nanocrystalline powders

Abstract Powder metallurgy was used to fabricate a bulk ultrafine grain size (UFG) Mg-3Al-Zn alloys. Nanocrystalline alloy powders with an average grain size of 45 nm were synthesized via ball milling of elemental powders of Mg, Al and Zn. The milled powders canned in Al containers were subjected to cold (at room temperature) or hot press (for 40 min at 633K), respectively, in a vacuum furnace. The sintered samples were extruded at 423 K to further solidify. The results show that the average grain size is 180 nm for the cold samples, and that is 600 nm for the hot samples. The cold-press alloys show a yield stress of 426 MPa. The high strength of UFG Mg is attributed to the fine grain strengthening mechanism resulting from the strong dependence of strength on the grain size for HCP metals. The consolidated samples of the cold-press and hot-press alloys have a final density of (1.777±0.006) and (1.800±0.006) g/cm 3 , respectively.

Microstructures of PM Ti–45Al–10Nb alloy fabricated by reactive sintering

Abstract Powder metallurgy Ti–45Al–10Nb alloys was successfully fabricated by reactive sintering of milled powders at 1350 °C for 2 h in vacuum. The microstructure, in particular, constituent phases, grain size, precipitates of the product was investigated in detail. The results indicate that a double phase γ + α 2 microstructure containing Ti 2 AlC precipitate is obtained under the sintering condition, and the alloy exhibits a fine and homogenous microstructure compared with traditional TiAl base. In fine grain structure, the average grain sizes for the γ and α 2 phases are (2.3±0.05) and (5.6±0.05) μm, respectively. Additionally, numerous dislocations are observed in the alloy, and the dislocation density in γ phase is significantly higher than that in α 2 phase. The formation mechanisms of the dislocation in the present alloy were also discussed in detail.

Effect of extrusion ratio on coating extrusion of Pb-GF composite wire by numerical simulation and experimental investigation

The extrusion ratio is one of the key parameters for manufacturing the lead-glass fiber (Pb-GF) composite wire by coating extrusion. The effect of extrusion ratio on coating extrusion of Pb-GF composite wire was studied by finite element numerical simulation with the use of the DEFOEM simulation software. The simulation result shows that the higher the extrusion ratio, the higher the effective stress that the glass fiber bears during extrusion. It is also observed that the extrusion force increases with the increase of the extrusion ratio. The extrusion experiment of Pb-GF composite wire reveals that extrusion ratio is changed by changing the quantity of glass fiber and composite diameter. The rule that increasing the extrusion ratio enhances the coating speed limit suggests that the load on the glass fiber increases with increasing extrusion ratio. Both the simulation and the extrusion experiments show that the extrusion force increases with increasing extrusion ratio.

Hydriding and microstructure nanocrystallization of ZK60 Mg alloy by reaction milling in hydrogen

Abstract The hydriding of as-cast Mg-5.5%Zn-0.6%Zr (ZK60 Mg) (mass fraction) alloy was achieved by room-temperature reaction milling in hydrogen, with the mechanical energy serving as the driving force for the process. The hydriding progress during milling was examined by hydrogen absorption measurement, and the microstructure change was characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The results show that, by room-temperature reaction milling in hydrogen, the as-cast ZK60 Mg alloy can be fully hydrided to form a nanocrystalline MgH 2 single-phase microstructure. In particular, the average grain size of the MgH 2 phase obtained by room-temperature reaction milling in hydrogen for 16.2 h is about 8–10 nm, and the average particle size of the as-milled hydrided powders is 2–3 μm.

Effect of Al and Zn additives on grain size of Mg-3Ni-2MnO2 alloy

The effect of Al and Zn additives on the grain size of Mg-3Ni-2MnO2 alloy was investigated. The nanostructured Mg-3Ni-2MnO2 and Mg-3Ni-2MnO2-3Al-Zn were made by ball milling process under hydrogen atmosphere. The XRD results and TEM analysis reveal that Al and Zn additives almost have no effect on the grain size of Mg-3Ni-2MnO2 alloy. The present study provides us a feasibility of producing nano-structured magnesium alloys, based on hydrogenation, disproportionation, desorption and recombination(HDDR), by adding beneficial elements to hydrogen storage materials.