Materials Science Forum Vols. 546-549

Abstract: Degradable implants have been in use for bone surgery for decades. However, degradable metal implants are one of the new research areas of biomaterials science. There is a potential for application of degradable metal implants as screws and plates in bones. Magnesium alloys are one of the new candidate materials for degradable implants. Magnesium has good biocompatibility due to its low toxicity, and it is a corroding, i.e. dissolvable, metal. Furthermore, magnesium is needed in human body, and naturally found in bone tissue. Mechanical properties of magnesium alloys are dimensionally comparable to the cortical bone substance. In this study, corrosion behavior of magnesium metal at the bone interface and the possibility of new bone cell formation have been investigated. Cortical bone screws were machined from magnesium alloy AZ31 extruded rod and implanted to hip-bones of sheep via surgery. Three months after surgery, the bone segments carrying these screws were removed from the sacrificed animals. Samples were sectioned to reveal Mg/bone interfaces and investigated using optical microscope, SEM-EDS and radiography. Optical and SEM images showed that there was a significant amount of corrosion on the magnesium screw. The elemental mapping results indicate, due to the presence of calcium and phosphorus elements, that there exists new bone formation at the interface. From the results of this study, it may be stated that the potential for using magnesium alloys as a bone implant material is expected to be significant.

Abstract: Microstructures and properties of rolled Mg-9Gd-4Y-0.6Mn（nominal wt%）sheets solution treated at 793K for 12h, and aged at various combinations of temperatures and time were investigated by hardness measurement, tensile test and TEM. The evolution of the precipitates and their effect on the mechanical properties of the pre-, peak-, and over-aged tempers were determined, and the optimal yield tensile strength (YTS) and ultimate tensile strength (UTS) were 276MPa and 287MPa at room temperature, respectively. It has been found that the addition of Mn into Mg-Gd-Y system contributes to block behavior of matrix diffuse and increase potential of heat resistance of the alloy.

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 microstructure and mechanical properties of Mg-3wt％Nd-0.2wt％Zn-0.4wt％Zr alloy in as-cast, solution-treated and solution-treated + peak-aged were investigated. The alloy had a cast structure with large intergranular Mg12Nd phase between the α-Mg matrix. After solution-treated, the intergranular Mg12Nd phase disappeared and lots of small Zr-containing particles distributed inside the grains. Small plate-like phases precipitated inside the grains strengthened the alloy to a high level after peak-aged at 200°C for 16 hours: the ultimate strength of the alloy up to 305 MPa, with considerable elongation rate 11%, and yield strength 140 MPa. The peak-aged samples also had good creep resistance, with strain rate less than 0.2% after 120 hours creep test under the condition of 110 MPa at 200°C. The minimum creep rate was about 4.64×10-9. The alloy had different fracture pattern in different states: as-cast state, intergranular fracture was the key pattern to failure; after solution-treated, the fracture pattern turned to cleavage transgranular fracture; after peak-aged, the alloy had a mixed fracture pattern of transgranular and intergranular, in which transgranular was the main style.

Abstract: The infiltration pressure field of fiber reinforced AZ91D was studied in this paper. The carbon fiber T300 was selected and covered with rough TiO2 coat by means of plasma techniques. These carbon fibers were combined together and a kind of continuous pre-former with many micro-passes was constructed. When this pre-former went though a infiltration cabin filled with molten magnesium alloys, the melt infiltrated into pre-former through those micro-passes under infiltration pressure. A physical model and related mathematic model were built to relate this process. The relationship among pressure (p), infiltration flow rate change (e) and the location of infiltration flow (r) was molded.

Abstract: The cathodic reduction of SiO2 in KCl-CaCl2-NaCl-MgCl2 melt was studied using tungsten wires as working electrodes. The results of cyclic voltammetry
square wave voltammetry and chronopotentiometry showed that the cathodic deposition of silicon is a quasi-reversible diffusion-controlled reaction, followed by a four electrons transfer step. The results of current reversal chronopotentiometry and thermodynamic data showed that both the silicon deposition and the side reaction between SiO2 and magnesium result in the loss of magnesium and low current efficiency. A 35.2% current efficiency was obtained with the content of SiO2 0.2% at 700 .

Abstract: Expulsion is undesirable during the resistance spot welding due to the weld quality decrease. The expulsion happening during the resistance spot welding of AZ31B magnesium alloy was studied related to the distribution of maximum temperature in the interface due to the existing of contact resistance, and connected with the increased pressure in the nugget due to melting and expansion of liquid metal. The influence of welding parameters on expulsion is presented and discussed in this investigation.

Abstract: In the present work Miedema model has been developed, and the formation enthalpy of Mg-Zn alloys and the activity curve of Zn in Mg-Zn alloy at 1000K have been calculated according to the Miedema model. The calculation results showed that the formation enthalpy of Mg-Zn was small, and the excess entropy attributes a lot to the result. When excess enthopy was considered, the calculation results were found to be in good agreement with the experimental values.

Abstract: In order to make full use of magnesium alloy resources under the environment of the network, an integrated magnesium alloy database system prototype has been developed, which consists of five modules, including database utilizing, files management, report printing, data inquiry and system utilities. This system gives more conveniences to user’s work by adopting three-tier architecture and using advanced technologies such as ASP (Active Server Pages). The user who only owns a global browser can conveniently use this database system without pre-installing any other application softwares. This database system prototype is a powerful tool to cut down the cost and time for developing new magnesium alloys.

Abstract: Mg2-yAlyNi(y=0,0.2,0.3,0.4) and Mg2-aTiaNi (a=0.1,0.2,0.3,0.4) were successfully synthesized by two-step process. The phase composition, microstructure and morphology of the alloys were determined by XRD and SEM. It was found that their main phase was Mg2Ni and another phase, Mg3AlNi2, was observed when Mg in Mg2Ni was partially substituted by Al. The SEM observations showed a large amount of white grains were uniformly distributed in the matrix of the alloys substituted by Al, Ti and the variation of microstructure led to promoted electrochemical properties.