Chang Shu He

Calculation of Magnetization and Phase Equilibrium in Fe-C Binary System under a Magnetic Field

The Weiss model is extended by substituting the molecular field coefficient lwith a short-range-ordering coefficient g valid around and above Tc. The temperature variations of susceptibility of fcc Fe are calculated with a band model. Based on the above models, the phase equilibrium diagram of Fe-C binary system under a magnetic field is calculated.

Characteristics of Recrystallization Texture Evolution in High Magnetic Field for Interstitial Free (IF) Steel Sheet

High magnetic field is applied with the field direction parallel to the rolling direction during annealing of a cold rolled IF steel sheet. Results of X-ray ODF analysis show that, magnetic field annealing retards the normal recrystallization texture evolution for the IF steel sheet. It is worth noting that an abnormal increase of orientation intensity at {100}<110> is found after magnetic annealing for 25min at 650°C. When the magnetic field strength is increased from 10 Tesla to 14 Tesla, the a-fiber is further strengthened, especially the {100}<110> component. Combined with EBSD analysis results, it is considered that the magnetic field does not change the mechanism of recrystallization texture evolution for the IF steel sheet in the present case.

Textures and Local Textures in Severely Cold-Rolled and Annealed Ultra-Fine-Grained FeCo Alloy

We find that a severely rolled FeCo alloy has anomalous enhancement of the rotated-cube {100}<011> texture component and a decrease of the {111} components after annealing, which is contrast to the recrystallization behaviors reported in traditional BCC metals and alloys. The local texture measurements show that two kinds of grains with obviously different orientations, i.e. {100} and {111}, are heterogeneously distributed in the deformed specimen and the migration of high-angle grain boundaries is observed after annealing in the disordering temperature region.

Texture Evolution in Nanocrystalline Fe Induced by Surface Mechanical Attrition Treatment

The texture evolution of the pure iron sample after the surface mechanical attrition treatment (SMAT) was investigated by means of electron backscattering and X-ray diffraction (XRD) analysis. Experimental observations indicated that four sections along depth were formed in the pure iron sample during the SMAT, i.e., nanostructured regime in the surface layer, submicro-sized, micro-sized and plastic deformed regime. Compared to the microstructure of sample, texture analysis was performed. It can be found that the <110>//ND fiber texture is the prominent texture. A strong orientation of (110)[11] along the <110>//ND fiber was formed in the plastic deformed regime, and as the depth from the top surface decreases, <110> //ND fiber texture intensity increases. The maximum intensity was reached in the micro-sized regime, and then it start to reduce. In the nanostructured regime, <110> //ND fiber texture nearly disappear.

Effects of High Magnetic Field Heat Treatment on the Microstructure of Fe-0.76%C Alloy

The present studies are to investigate the microstructure features during transformation from austenite to ferrite without and with magnetic field on Fe-0.76%C alloy. It is found that the area fraction and numbers of proeutectoid ferrite grain as well as the lamellar spacing of pearlite in Fe-0.76%C alloy increased considerably with the increase of magnetic field intensity. The reason is that, the magnetic field increases the driving force of proeutectoid ferrite nuclei and shifts the eutectoid point to the side of high carbon content and high temperature, which increases the starting-temperature of the transformation from austenite to ferrite. The proeutectoid ferrite grains are elongated along the magnetic field direction, which can be explained as follows: the proeutectoid ferrite becomes the magnetic dipolar under high magnetic field, and then the polarized austenite atoms are much easier to diffuse into ferrite grains along the magnetic field direction. Key words: high magnetic field; Fe-0.76%C alloy; microstructure

Characteristics of Microstructure and Texture in the Stir Zone of Friction Stir Welded Al-12.7Si-0.7Mg Alloy

4-mm thick Al-12.7Si-0.7Mg alloy plates were cut from the hot extrusion profiles. A butt-welding joint was made by friction stir welding (FSW). Optical microscopy and SEM-EBSD analysis were employed to examine the microstructure and texture evolution in the stir zone of the joint. This work provides basic information for microstructure and microtexture characteristics in the stir zone after FSW for this novel wrought Al-Si alloy.

Effects of High Magnetic Field and Field Direction on Recrystallization and Recrystallization Texture in Cold-Rolled IF Steel Sheet

The effects of magnetic annealing on recrystallization and texture evolution in asannealed interstitial-free (IF) steel sheet were investigated by means of X-ray diffraction ODF analysis, SEM-EBSD analysis, and optical microstructure observation. During the magnetic annealing, specimens were placed at the center of the applied magnetic field, with their rolling planes parallel to the field direction (MD) and their rolling direction (RD) normal to the field direction (MD). It was found that the magnetic annealing retards the recrystallization process, but promotes the nucleation at the initial stage of recrystallization. Magnetic annealing did not change the mechanism of recrystallization texture evolution but improved the development of γ-fiber texture during the process of recrystallization, and the magnetically annealed specimen had stronger γ-fiber texture compared with the conventionally annealed specimen; this interesting finding is quite different from the previous work on magnetically annealed IF steel.

Effect of Heat Treatment on Positron Annihilation Lifetime of an Extruded Al-12.7Si-0.7Mg Alloy

Positron annihilation lifetime can reflect the information of electronic density. Therefore this technique is very sensitive to the vacancies. Therefore positron annihilation technology (PAT) is a non-destructive testing technology for the investigation on the vacancy in pure metals and alloys. The vacancy defects of as-cast pure aluminium and the extruded Al-12.7Si-0.7Mg alloy before and after heat treatment were investigated by positron annihilation lifetime spectra. The results of positron annihilation lifetime spectra show that the lifetime of free positron annihilation in the pure aluminium alloy is 155 ps. The positron annihilation lifetime of the extruded sample is longer than the lifetime in the pure aluminium due to the formation of grain boundary and dislocation during the extrusion process. The positron annihilation lifetime of the extruded sample after heat treatment is shorter than that before the heat treatment, and it is longer than that of the pure sample.

Mechanical Spectra of an Al-12.7Si-0.7Mg Alloy under Extrusion and T6 States

Mechanical spectra of an Al-12.7Si-0.7Mg alloy under extrusion and the solid solution treatment followed artificial aging (T6) states were measured at different frequencies. It has been found that their spectra present differences. There was an obvious internal friction peak near to 200°C with increasing the temperature. The value of internal friction presented increase started from 300°Cand height of the peak was low, there existed a peak near to 270°C during the cooling processes in the spectrum for the extrusion state. For the T6 state alloy, no peaks could be observed during the heating processes. With decreasing the temperature, the internal friction peaks were again observed near 200°C and 270°C.

Preparation and Evaluation of a Novel Al-5.4Si-0.5Mg Welding Wire

An Al-5.4Si-0.5Mg filler wire was developed and produced by direct chill (DC) casting, extrusion, and roll-die and hole-die drawing for the welding of newly developed Mg-containing high-Si aluminum alloys. The Al-12.7Si-0.7Mg alloy plates were butt-welded by tungsten inert gas arc welding (TIG) method using the as-produced welding wire. The microstructures and mechanical properties of these welded joints in different solid solution and artificial aging treatment conditions were studied to evaluate the weld qualities of the novel welding wire. The results showed that the Al-5.4Si-0.5Mg welding wire was an ideal special welding wire of the Al-12.7Si-0.7Mg alloy and the filler metal proved to be heat-treatable. The welded joints exhibited much higher mechanical properties after the post-weld heat treatment (PWHT). All of this provides the possibility of wide application of the novel Al-5.4Si-0.5Mg welding wire and the Al-12.7Si-0.7Mg alloy weldments.