Advanced Materials Research Vols. 311-313

Abstract: Solidification behaviour of Pb-Bi alloys under rotating magnetic field (RMF) was investigated experimentally to understand the effect of the frequency of RMF on the nucleation and growth behaviour. It was found that, as the increase of the rotating frequency, the grains are fragmented and refined gradually until a transition from columnar to equiaxed microstructures happens at a rotating frequency of 40 Hz. Moreover, the Bi concentration of the primary phase decreases and macrosegregation is eliminated effectively with RMF. These are due to the effect of RMF on the nucleation, growth and fluid flow in the solidification process.

Abstract: A strong basal plane texture of AZ31 magnesium alloy was obtained by severe hot-rolling with three passes falling temperature. The effects of annealing time and annealing temperature on the evolution of texture at different layers were studied by means of X-ray texture analysis. The results showed that the orientation density of basal plane texture component was reduced greatly tending to dispersion with increasing annealing time and temperature. The hard orientation can be greatly weakened by softening annealing, the best basal plane orientation was obtained when the annealing time is 60min and the annealing temperature is 150~300°C. A texture gradient along thickness direction with annealing has been found in the sheet. The texture gradient was the lowest when the annealing time is 60min and the annealing temperature is 300°C.

Abstract: Through methods, such as microscope analysis, mechanical analysis, chemical analysis, metallographic examination, the causes resulting in tee joint crack of subcritical power station boiler final superheater header (12Cr1MoV) have been analyzed. The result indicates the tee joint crack is reheat crack, and irrational structure and excessive welding residual stress are the primary inducement of tube joint crack.

Abstract: 7A52 Al alloy plates was welded using twin-wire metal inert gas arc welding (TMW) .Stress corrosion cracking (SCC)behavior of the parent material and the welded specimens was investigated by the slow strain rate tensile(SSRT)test method respectively. Electrochemical impedance spectroscopy (EIS) was conducted to understand electrochemical corrosion behavior of 7A52 Al alloy and its TMW weldment. It was found that the welded specimens exhibited higher SCC susceptibility than the parent materials under SSRT testing in seawater. The EIS result showed that the weld zone exhibited higher corrosion resistance than that of the parent material. Hydrogen embrittlement is a crucial factor that leads to the failure of the welded specimens during SSRT test in seawater.

Abstract: CPM9V high speed steel(HSS) ring billet was prepared by spray forming(SF), the yield is 83.5%, porosity is 0.8%, spray forming preparation method and technological parameter were illustrated. The microstructure and carbide morphology on the different position of billet were observed. The results show that carbide particles have small size, regular shape and uniform distribution, alloy element without segregation. There are some pores and defects in the position of ring billet closed to deposition substrate, come from spray forming instability beginning stage.

Abstract: In this research, the oxidation and melting behaviour of AZ91D magnesium alloy granules was investigated throughout using in-situ melting technique when the granules were covered by flux. The granules were heated inside an electrical resistance furnace at four different temperatures of 650, 700, 750 and 800 °C for 30 min. Thermal analysis was used to detect the granules characteristic temperatures during the technique. The products of the heating process were examined visually and characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that due to occurrence of severe oxidation and combustion, particularly at 800 °C, a significant amount of the granules transformed to a powdered state. The presence of the mould materials within the oxidation residue was detected indicating that severe mould-magnesium reaction occurred during heating. It was found that the granules melted during the heating process. However, the presence of oxides on the granules prevented them from fusing to form a single melt.

Abstract: In this paper, we systematically investigated the influence of SiC particle size on the wear properties of the SiC particle reinforced Cu matrix composite prepared by powder metallurgy process. Under low load (≤120N), the increase of the SiC particle size contributes to the improvement of the abrasive resistance and the main abrasion mechanism is abrasive wear. With the increase of the load, the large SiC particle is easy to break and exfoliate, leading to delamination wear and the decrease of the strength. Under higher load (≥120N), the small size of the SiC reinforcement particle which can reduce the plastic deformation of the subsurface efficiently has significant enhancement effect of the SiC/Cu composite, avoiding delamination fracture.

Abstract: In this paper, the influence of temperature and strain rate on the superplastic deformation behaviors of the Mg-Zn-Nd alloy has been investigated through performing tensile tests at different temperatures and strain rates. After 4 passes of ECAP by route C, the strain-rate sensitivity coefficients reached 0.32 at 300°C, indicating that the ECAPed Mg-Zn-Nd alloy exhibited a good superplasticity at lower temperature. The results of flow activation energy showed that the super-plastic deformation mechanism of magnesium alloys is grain-boundary sliding controlled by grain boundary diffusion.

Abstract: This paper proposes an intelligence control system of heat balance for aluminum reduction cell and reviews in each period the control technique of aluminum electrolysis at home and abroad. Mutual coupled relations of physical fields such as electric field, magnetic field, flow distribution, thermal field, stress field, concentration field in aluminum reduction cell are analyzed simply. In this system automatic control of furnace temperature and liquidus temperature in aluminum electrolyte are detected in real-time accurately. This control system can reduce the superheat of aluminum reduction cell in a certain range, and reduce production cost of per ton of primary aluminum on maximal degree. Thus, energy consumption and waste is decreased and heat balance in aluminum electrolysis is realized, efficient operations are certified in the product of aluminum electrolysis.

Abstract: The purpose of the present study was to discuss the effects of local solidification time on porosity content of long solidification range A201 aluminum alloy plate castings. With systematic change in the riser size, together with variation of thickness and length, were cast in different kinds of molds. The sand molds with end chill for the plate castings were made of 100% silica sand. The porosity content of A201 aluminum alloy was affected by the local solidification time in this study. The correlation between porosity content and solidification time is found to be split into 2 bands, each being associated with one of the two thickness of plate castings.