Er-de Wang

Mechanical properties and texture evolution during hot rolling of AZ31 magnesium alloy

Abstract Mechanical properties and texture evolutions of the as-rolled AZ31 Mg sheets were investigated. The results show that the grains of the sheets are significantly refined after hot rolling. The mechanical properties of the as-rolled samples are enhanced due to the grain size refinement. The intensity of basal texture decreases with the increase of deformation ratio, and double-peak type basal texture is discovered in the intermediate and large strain hot rolling processes. The formation of the texture is ascribed to the activities of prismatic and non-basal c + a > slips, which is the same as the 30% rolled and 50% rolled samples. The incline of basal planes exerts an effect on the mechanical anisotropy during tension along rolling direction (RD) and transverse direction (TD) at room temperature.

Grain refining and property improvement of AZ31 Mg alloy by hot rolling

Abstract Hot rolling of AZ31 Mg alloy was performed by using as-cast alloy ingot as the starting material. The microstructures and mechanical properties of the as-rolled alloy subjected to various rolling passes were investigated. The results show that the grain size of the alloy can be refined steadily with increasing rolling passes by dynamic recrystallization. With the steady refining of the grain size, both the mechanical strength and the plasticity of the alloy are improved correspondingly. In particular, when the grain size is reduced to about 5 μm after 5 rolling passes, the yield strength, ultimate tensile strength and tensile fracture strain of the alloy are 211 MPa, 280 MPa and 0.28 in the transverse direction, they are 200 MPa, 268 MPa and 0.32 in the rolling direction, respectively.

Effects of deformation on microstructures and properties of submicron crystalline Cu-5%Cr alloy

Warm extrusion of submicron crystalline Cu-5%Cr from 100℃ to 600℃ was investigated. The effects of different extrusion ratios and different extrusion temperatures on microstructures and properties of submicron crystalline Cu-5%Cr were studied. The microstructures of the extruded Cu-5%Cr were characterized by backscattered electron images(BSE) and transmission electron microscopy(TEM). The mechanical properties of the extruded Cu-5%Cr were measured by means of microhardness and tension test. The results show that, the deformation, dynamic recovery and dynamic recrystallization of the extruded Cu-5%Cr are mainly produced in Cu matrix. The higher extrusion ratio leads to more uniform microstructure and finer Cu grains. When being extruded in the range of 100-600℃, dynamic recovery of Cu is the dominant process, and dynamic recrystallization of Cu occurred above 300 ℃ is far from end. The most part of microstructure of as-extruded Cu-5%Cr is subcrystallines produced by dynamic recovery, only a few recrystallines exist, and the average size of these grains is not larger than 400 nm. With extrusion temperature rising, the tensile strength and microhardness of Cu-5%Cr decrease, and elongation increases gradually.

Working hardening behaviors of severely cold deformed and fine-grained AZ31 Mg alloys at room temperature

Abstract AZ31 Mg alloy extrusion wires were drawn to a maximum cumulative area reduction of 61% at room temperature, and the 61%–drawn sample was subjected to various annealing treatments for grain refinement. Tensile tests were performed on all the as-drawn and as-annealed samples at a constant strain rate at room temperature. The entire stress—strain curves of each investigated sample were analyzed for the dependence on drawn area reduction and mean grain size. The results show that the cold drawn samples exhibit a constant elastic modulus; however, the stresses are significantly dependent on the deformation level. The corresponding θ—σ curves (where θ is the strain hardening rate, dσ/dɛ) show extended stage II and suppressed stage IV of strain hardening. The recrystallized samples exhibit enhanced yield stress with the grain size refinement and typical hardening stages of polycrystalline metals: II, III, IV and V. Additionally, decreasing in stage IV with refining grain size is observed probably due to the contribution of grain boundaries slipping. The different hardening behaviors demonstrate the various hardening mechanisms between the cold drawn and recrystallized materials.

Effect of hot rolling on grain refining and mechanical properties of AZ40 magnesium alloy

AZ40 Mg alloy thin sheets were prepared by multi-pass hot rolling with the hot-extruded alloy as the starting material. The effect of hot rolling on the microstructure, mechanical properties, and fracture behavior of the alloy was investigated. The results show that the microstructure homogeneity can be improved and the grain size is refined steadily by dynamic recrystallization with increasing rolling passes. As a consequence, the mechanical properties of the as-rolled sheets are improved significantly as compared with the starting as-extruded alloy. By 5 or more rolling passes, the average grain size is reduced to no more than 10 μm, and the yield strength and the tensile elongation of the sheets prepared achieve as high as more than 175 MPa and 20%, respectively, in both the rolling and the transverse direction.

Microstructure stability of cold drawn AZ31 magnesium alloy during annealing process

Abstract The microstructural evolution of heavily cold drawn AZ31 magnesium alloy wires was investigated during a wide range of annealing temperature from 200 to 450°C. The results show that the mean grain size of the as-annealed material is sensitive to the annealing temperature and cold drawn area reduction. Upon annealing symmetrical grain growth takes place in the AZ31 wires of cold drawn area reduction 12.2% under all the investigated annealing conditions, while three different stages of grain size refinement, normal grain growth and abnormal grain coarsening occur gradually in the materials with cold drawn area reduction 23.0%–60.5% with annealing temperature increasing. The increase of cold drawn reduction leads to the decrease of critical annealing temperatures for the three periods, and also enhances the start of abnormal growing grains preferentially in the severely drawn materials from the outer surface where larger amount of shear deformation constitutes the driving force for growth.

Microstructures and properties of cold drawn and annealed submicron crystalline Cu-5%Cr alloy

Abstract The microstructures and properties after cold drawing and subsequent annealing of submicron crystalline Cu-5%Cr (mass fraction) alloy were investigated. The results show that, the microstructure of submicron crystalline Cu-5%Cr can be further refined by cold drawing. After cold drawing, the grains of Cu-5%Cr alloy with grain size of 400–500 nm can be refined to be cellular structures and subgrains with size of 100–200 nm. Both strength and ductility of Cu-5%Cr alloy can be enhanced by cold drawing, and the optimal mechanical properties can be achieved with drawing deformation increasing. It is suggested that dislocation glide is still the main mechanism in plastic deformation of submicron crystalline Cu-5%Cr, but grain boundary slide and diffusion may play more and more important roles with drawing deformation increasing. When the cold drawn Cu-5%Cr wires are annealed at 550 °C, fine recrystal grains with grain size of 200–300 nm can be obtained. Furthermore, there are lots of fine Cr particles precipitated during annealing, by which the recrystallization softening temperatures of the cold drawn Cu-5%Cr wires can be increased to 480–560 °C. Due to the fact that Cr particles have the effect of restricting Cu grains growth, a favorable structural thermal stability of the submicron crystalline Cu-5%Cr can be achieved, and the submicron grained microstructure can be retained at high temperature annealing.

Nanocrystalline Mg and Mg alloy powders by hydriding-dehydriding processing

Abstract The process of mechanically assisted hydriding and subsequent thermal dehydriding was proposed to produce nanocrystalline Mg and Mg alloy powders using pure Mg and Mg-5.5%Zn-0.6%Zr (mass fraction) (ZK60 Mg) alloy as the starting materal. The hydriding was achieved by room-temperature reaction milling in hydrogen. The dehydriding was carried out by vacuum annealing of the as-milled powders. The microstructure and morphology of both the as-milled and subsequently dehydrided powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), respectively. The results show that, by reaction milling in hydrogen, both Mg and ZK60 Mg alloy can be fully hydrided to form nanocrystalline MgH 2 with an average grain size of 10 nm. After subsequent thermal dehydriding at 300 °C, the MgH 2 can be turned into Mg again, and the newly formed Mg grains are nanocrystallines, with an average grain size of 25 nm.

Effects of milling and crystallization conditions on microstructure of Nd2Fe14B/α-Fe powder

Abstract Effects of milling and crystallization conditions on microstructure, such as amorphous phase and nanocrystalline phase, were investigated by X-ray diffractometry(XRD), differential scanning calorimetry(DSC), and transmission electron microscopy (TEM), respectively. The results show that nanocomposite Nd 2 Fe 14 B/α-Fe powder can be prepared by mechanical milling in argon atmosphere and a subsequent vacuum annealing treatment. The grain sizes of both Nd 2 Fe 14 B and α-Fe phase decrease drastically with increasing milling time. After milling for 5 h, the as-milled material consists of α-Fe nanocomposite phases with the grain size of 10 nm, and some amorphous phases, which can be turned into Nd 2 Fe 14 B/α-Fe nanocomposite phases by the subsequent annealing treatment. Milling energy of mechanical milling after 5 h by theoretical calculation is 6 154.25 kJ/g.

Desorption behaviour and microstructure change of nanostructured hydrided AZ31 Mg alloy powders

Abstract In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment, nano-structured as-hydrided Mg-3%Al-1%Zn (AZ31 Mg) (mass fraction) alloy powders were thermally dehydrided at various temperatures from 275 to 375 °C. The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding. The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM), respectively. Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature. The higher the temperature, the faster the desorption, and the more significant the grain growth. When the desorption temperature was raised from 300 to 375 °C, the time to achieve complete dehydriding was shortened from 190 to 20 min, and the average grain size increased correspondingly from 20 to 58 nm.