The forces acting on the sphere in front of the S/L interface during the solidification of immiscible alloys have been analyzed. The dynamic criterion for the interaction mode between the sphere and solidification interface has been proposed. Combining theory with experiment, the effect of the interaction between the S/L interface and the sphere on the microstructure development in the Al-Bi based immiscible alloy has been discussed in detail. The results have indicated that the small Bi-rich spheres were repelled and accumulated in front of the solidification interface due to the combined action of the interfacial repulsion and Marangoni migration. If the interface morphology is dendritic or cellular, the Bi-rich sphere with critical size is partially entrapped by the interface and forms tadpole-type particle. While, the smaller Bi-rich spheres will be entrapped in the interdendrite and the Bi-rich particles distribute at the grain boundaries and the triple junctions after solidification.

The directional solidification experiment of Al-Bi immiscible alloys has been carried out by using the self-made equipment with the applied magnetic field. The effect of the magnetic field strength on the microstructure was investigated. Also, the effects of the magnetic field on the sphere’s nucleation, spatial motion and the collision and coagulation between spheres have been analyzed theoretically. The results show that both the motion velocity and the probability of the collision and coagulation are availably reduced due to the applied magnetic field. It indicates that the larger the magnetic field strength, the smaller the average size of Bi-rich spheres is and the more dispersedly the spheres distribute.

The directional solidification experiment has been carried out for the Al-Bi based immiscible alloys. The effect of the addition element Si or Cu and the content on the solidification microstructure was investigated. The results show that both Si and Cu accelerate the coarsening of the Bi-rich sphere, and the addition of Si is more obvious than the element Cu to do under the same experimental condition. The change of the free energy, liquid-liquid interfacial energy and liquid viscosity due to the addition has been analyzed. Also, the effect of the change on the solidification process was discussed in detail. This investigation will enrich the understanding of the solidification feature of the ternary immiscible alloys.

The effect of acicular ferrite (AF) microstructure composition of different phases on the strength of X65 pipeline steel was investigated by varying thermo-mechanical control process (TMCP) parameters to the steel. Experimental results showed that lowering the finish rolling temperature or increasing the cooling rate was in favor of formation of the granular ferrite and the bainite ferrite in AF microstructure, thus obviously increasing the strength of the steel. Enhancing the coiling temperature could accelerate the perception strengthening, also in favor of the strength for the steel. However, lowering the finish rolling temperature made the most contribution to the increase of the strength.

The carbides of lower bainite is main constituent of bainite structure. The purpose of this paper is to clarify that where the lower bainitic carbides come from. Therefore ,three things have been completed in this paper:1. By using three group of experiment,the results indicate that the lower bainitic carbides can nucleate in the g side of a/g interface or between two bainitic ferrite sub-units and grow towards austenite. The carbides can exist across the interface of a/g or a/a.2. The results of another experiment indicate that the essence of phenomenon that lower bainitic carbides exist inside the ferrite is lower bainitic carbides precipitate from the g side at a/g interface. The carbides grow competitively with the ferrite,during the whole transformation process. Meanwhile the growing rate of ferrite is higher than that of carbides. As a result, the carbides are surrounded by ferrite which may give us a false concept that the lower bainitic carbides are precipitated from bainitic ferrite.3. The nucleation and growth model of lower bainitic carbides is proprosed on the basic of thermodynamics and the ledge-wise growth theory. From what has been mentioned above,it is suggested that lower bainitic carbides precipitate from carbon-enriched retained austenite rather than supersaturated ferrite. The essential of this paper is to identify whether existing the carbon-supersaturated bainitic ferrite , which directly concerning the mechanism of bainitic transformation.

Among all the processing parameters which affect porous structure obtained by directional solidification of a solid/gas (e.g. metal/hydrogen) eutectic (Gasar), the gas pressure above melts and the superheating temperature of melts are the most observable and easily governed because they directly control the amount of hydrogen saturated in melts. The critical processing conditions for hydrogen to escape and for formation of lotus-type porous structure have been deduced through theoretical analysis and calculation, and the following conclusions have been obtained: both the superheating temperature and the argon partial pressure should have moderate values, viz. with given partial pressures of hydrogen and argon, the superheating temperature should be bigger than the threshold of formation of lotus-type structure and smaller than that of hydrogen to escape; however, with given superheat degree and hydrogen partial pressure, the argon partial pressure should be bigger than the threshold of hydrogen to escape and smaller than that of formation of lotus-type porous structure. These conclusions were verified by the experimental results of lotus-type porous Mg and will contribute to the fabrication of high-quality regular porous metals by Gasar process.

High pressure gas atomization experiments were done with Al-Pb immiscible alloy. Powders with a Pb-rich shell on their surfaces were obtained. A model describing the microstructure evolution in Al-Pb atomized droplet was developed. The solidification process was calculated. The results indicate that the formation of the shell-type structure is due to the heterogeneous nucleation of the Pb-rich phase on the atomized drop surface.

With considering the urgent requirement of high efficiency, high quality, and low consumables welding technologies, a novel high-speed arc welding process of low cost, i.e., DE-GMAW (double electrode-gas metal arc welding), is developed. It attaches a GTAW torch on conventional GMAW equipment to makes part of current flowing through the wire pass the bypass arc between the GTAW torch and the main arc. Thus, under the condition of larger current flowing through the wire to ensure high deposition rate, the heat input exerted on the base metal is decreased to avoid the contradictory which high-speed welding faces with, and high-speed arc welding is realized. A Finite-element analysis model suitable to DE-GMAW process is developed to conduct numerical simulation of temperature and stress-strain fields. The results show that the predicted and measured weld dimensions at cross section match well, and the weld dimension, heat-affected zone width, stress, strain and deformation in DE-GMAW are much lower than those in conventional GMAW under same welding conditions. It provides the basic data for optimize the process parameters in DE-GMAW.

In this paper, the two-phase model of globular equiaxed grain solidification has been used to compute the solidification process of Sn-3.5%Pb hollow billet under traveling magnetic field. The temperature gradient, cooing rate, solute concentration distribution and grain size are studied under different stirring velocities. The results show that the traveling magnetic field can result in a global circulation flow in the molten metal, the temperature field is uniformed and the grain size is refined which improve the solidification structure of hollow billet. However, the macro segregation is produced in the hollow billet by the forced flow. So, the stirring velocity should be controlled carefully during the casting of hollow billets.