Papers by Author: Pei Dao Ding

Abstract: Cycle capacities of Amorphous Mg-Ni alloys declined so fast therefore they can’t be used practically. In this paper，the influence of adding Ti on the discharge capacity and cycle stability of the alloys were investigated. Amorphous Mg1-xTixNi (x=0, 0.1, 0.2, 0.3) alloy powder was prepared successfully by mechanical alloying (MA). X-ray diffraction (XRD) results show that MgNi alloy formed completely amorphous phase after ball milling with 15h. But for Mg1-xTixNi (x=0.1, 0.2, 0.3) alloy, it took 23h. It can be concluded that Ti partial substituting Mg would decrease the amorphous phase forming ability of Mg-Ni based alloy. Compared with amorphous MgNi alloy, the maximal discharge capacities of Mg1-xTixNi (x=0.1, 0.2, 0.3) alloy were decreased slightly, but the cycle stabilities were significantly enhanced. Mg0.9Ti0.1Ni alloy showed the largest discharge capacity and the best cycle stability.

Abstract: In this paper，the influence of adding Al on the discharge capacity and cycle stability of amorphous MgNi-based hydrogen storage alloys were investigated. Amorphous Mg1-xAlxNi (x=0, 0.1, 0.2, 0.3) alloy powder was prepared successfully by mechanical alloying (MA). X-ray diffraction (XRD) results show that after ball milling with 15h, MgNi alloy formed completely amorphous phase. But for Mg1-xAlxNi (x=0.1, 0.2, 0.3) alloy, it took 30h. It can be concluded that Al partial substituting Mg would decrease the amorphous phase forming ability of Mg-Ni Based Alloy. The discharge capacities and cycle stabilities of these alloys were tested. Compared with amorphous MgNi alloy, the discharge capacities of Mg1-xAlxNi (x=0.1, 0.2, 0.3) alloy were decreased slightly, but the cycle stabilities were significantly enhanced. Mg0.9Al0.1Ni alloy showed the largest discharge capacity and Mg0.8Al0.2Ni alloy showed the best cycle stability. Over all, ternary Mg0.8Al0.1Ni alloy showed the best synthesis properties.

Abstract: The AZ31 thin sheet (minimum thickness less than 1mm) was obtained by rolling the cast strip which was prepared by vertical twin roll casting in this paper. Since the absolute deformation during rolling was smaller,due to the small thickness of the strip of 3mm, the rolling of cast strip was different from the conventional rolling process. It was found that homogenizing time at 400°C for the cast strip was 4h and reduction per pass should be 8-10% for producing thinner (1-1.5mm) rolled AZ31 sheet at 350°C. Mechanical properties of the sheet were equivalent to conventional rolling sheet’s.

Abstract: Amorphous Mg-Ni alloy was prepared by mechanical alloying (MA). The state of the amorphous phase was analyzed by X-ray diffraction (XRD). The hydrogen desorption capabilities and electrochemical properties were tested. The analysis of the relationship among the ball-milling parameters, microstructures and properties of the alloy showed that the milling velocities have a critical influence on the formation of Mg-Ni amorphous phase. The higher the milling velocity is, the less the forming time of the amorphous phase is. And with the increasing of the ball-milling time, the amount of Mg-Ni amorphous phase increases. Whereas the hydrogen desorption capabilities and electrochemical properties will decrease if the alloy is ball-milled for a long time after the complete amorphization occurs. Mg, Ni atom ratio also has some obvious influence on the formation of the amorphous phase and the properties of the alloy. Increasing the content of Ni appropriately will improve the efficiency of formation of the amorphous phase, the hydrogen desorption capabilities and electrochemical properties of the alloy.

Abstract: The strip casting of AZ31 were carried out by a Ø250×150mm of vertical twin roll caster at different casting speeds (9-15m/min) and in different casting temperatures (630-660°C). The solidification microstructure of the strips was examined. The experiment results showed that the crystal grain size of the casting was smaller than that of conventional ingot, and decreases while the casting speed is raised, or the casting temperature decrease. The casting temperature strongly affected the dendrite structure that changed into sphere-like when the casting temperature was lower. The appropriate casting temperature for AZ31 magnesium alloy is 640°C, nearby its liquidus temperature.

Abstract: The simulation rolling and actual rolling of AZ31 strip with a thickness of 3mm prepared by a vertical twin roll caster (Ø250×150mm) have been made by both Gleeble-1500D thermal simulation testing machine and Ø170×300mm rolling-mill. The influence of various rolling parameters such as temperature (250°C, 300°C, 350°C and 400°C) and reduction (40%, 50% and 60%) on the microstructure of the rolled AZ31B thin strip have been investigated by means of metallographic observation and grain size measurment. The results indicate that when the temperature increases, the grain size of the rolled strip increases and the uniformity decreases. When the reduction is 50% the grain size is 10~30μm and the grains are fine and uniform. When the reduction is 40% or 60%, the grain size is 5~180μm and the grains are coarse in some areas. An optimized rolling process, 350°C×50% is suggested for actual rolling and a uniform microstructure of rolled AZ31 strip is obtained.

Abstract: Conventional production process of magnesium alloy strips involves many steps, including multi-hot rolling and multi-heat treatment, which is time-consuming and needs high energy cost. By use of thin strip casting, magnesium alloy cast strip with a thickness of less than 8mm can be produced and then rolled to the strip of the needed thickness, which is a short, energy saving and high effective process. In this paper, development of magnesium alloy strips prepared by single and twin roll casting has been summarized. Existing problems have been discussed and its development trends pointed out. Magnesium alloy strips prepared by single roll casting are suitable for Mg-based functional materials but not for structural materials because of low quality or high cost. Horizontal twin roll casting of magnesium alloy, based on aluminium alloy thin strip casting, has been industrialized in Australia and is close to industrialization in China. Vertical twin roll casting of magnesium alloy, based on steel thin strip casting, can reach a speed of more than 30m/min and higher productivity, but the process stability is lower and its research and development is just beginning. Horizontal twin roll casting should be developed for the thicker cast strip, more than 4mm thick, while vertical twin roll casting for the thinner, less than 4mm.

Abstract: The effects of homogenization on the formability for hot deformation of ZM21 wrought magnesium alloys was investigated. The alloys were produced by semi-continuous casting. Experiments including homogenizing annealing, micro-hardness testing and hot compress testing on Gleeble 1500D thermal simulator were carried out. The suggested homogenization parameters from the experimental results for ZM21 alloy is 400
C×12h.

Abstract: In this paper, the flow stress curves during thermal deformation of AZ61B magnesium alloy have been measured by isothermal compression tests on Gleeble-1500D thermal simulation instrument, and effects of deformation temperature and strain rate on flow stress were analyzed. The thermal deformation activation energy of AZ61B alloy could be work out at 185.64 KJ/mol by means of empiric dynamic equation of elevated temperature deformation. The softening mechanism of AZ61B alloy under the testing condition of thermal deformation has been identified to be dynamic recrystallization.

Abstract: Magnesium has a hexagonal close-packed crystal structure which makes it more difficult to deform than aluminum. Conventional strip production usually requires several process steps to reach the final strip thickness. Strip casting can reduce some of the process steps and make strip processing simpler and easier, especially for alloys with poor deformability. The twin-roll casting process can directly obtain strips with thickness less than one or two millimeters. In this paper, the metallurgical characteristics of the twin-roll strip casting process were analyzed and discussed. A laboratory scale vertical twin roll caster in prepared AZ31 magnesium alloy strips, with 1.0 to 2.0 mm thick and 150mm wide. Process stability in the thin strip casting process of the alloy has been studied, the casting temperature (superheat) was proven to be a key factor influencing process stability and casting strip quality. The as-cast microstructure of the alloy was analyzed and evaluated by optical microscopy, which showed that the as-cast microstructure was composed of developed dendrites when the superheat was high, and of a rosebush-like structure when the superheat was low. When the casting temperature was close to the liquid phase temperature，the as-cast microstructure became global or grainy, and the grain size of the cast strip was very small. This remarkably improved the deformability of the as-cast strip.