Materials Science Forum Vols. 546-549

Abstract: Recently, there has been an increasing interest in magnesium as biomaterials due to its similar elastic modulus, density and strength to that of human bone than other currently popularly used metallic biomaterials. However, the knowledge of its biocompatibility is lacking. This paper reports the results of testing the cytotoxicity, haemolysis and acute toxicity on untreated and treated magnesium samples. The results showed that no cytotoxicity was detected on untreated magnesium samples. However, samples of alkali-treated magnesium caused distinct morphological changes on cells with a reduction in cell number vs the control group. In haemolysis tests, untreated magnesium showed a haemolytic effect, whereas there was a small haemolytic effect (2.2%) on alkali heat-treated metal; this is less than the allowable 5%. Magnesium samples coated with an organic film show the lowest haemolytic effect. No acute toxicity was observed; no animal deaths occurred and we observed no obvious weight differences in untreated magnesium vs organic coated samples compared to the control group.

Abstract: At the present Mg-Sr alloy is usually produced by alloy mixing process or melt-leaching-reduction process which has low productivity. A new process has been developed termed “Preparation Mg-Sr alloys using vacuum thermal reduction”. The principle and procedure of the new process were discussed in this paper. The reduction thermodynamics was analyzed, including establishing the oxygen potential diagram of Sr, Mg, Si and Al, determination of main reactions, and evaluation of Gibbs free energy in vacuum. The results showed that Mg-Sr alloys can be obtained by synchronous reduction of SrO and MgO from a mixture of MgO, SrO, Si, CaO. The equipment, reduction temperature and vacuum for the new process have been also discussed.

Abstract: Application of magnesium alloy is restricted by its bad formability and low corrosion resistance. In order to resolve these problems, rolling-bonding has been tried as a new method. Pre-heating, rolling and annealing were used in the process of bonding, and aluminum cladding magnesium alloys obtained. The effects of many parameters in the processes of pre-heating, rolling and heat-treatment on bonding strength have been analyzed, and the mechanism of rolling-bonding been studied. It was found that intermediate phase played an important role in the bonding. Good bonding of aluminum cladding magnesium alloys achieved after annealing at 200oC for 1 hour.

Abstract: Nickel foam reinforced AZ91 magnesium alloy was fabricated by using melt infiltration and water quenching methods. The mechanical properties were measured in compressive and tensile deformation modes. Fracture surfaces were examined by scanning electronic microscopy. The results show that addition of nickel foam results in a significant increase in elastic modulus, yield strength of the composite material. However, ductility of the composite was adversely affected when compared to the unreinforced monolithic counterpart.

Abstract: The effect of heat treatment on mechanical prosperities of Mg65Cu25Gd10 glass has been studied in this paper. The thermal stability and the structure of as-spun and heat treated Mg65Cu25Gd10 alloys were examined by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The compression tests were performed using a computer controlled tensile test machine. Extended X-ray absorption fine structure (EXAFS) was applied to study the structural changes of Mg65Cu25Gd10 glass during annealing. Results showed that the decline of mechanical properties for Mg65Cu25Gd10 glass after annealing was closely related to the changes in local environment of Cu atoms and appearance of crystalline phases, and not the Gd local structure.

Abstract: ab-initio calculations on the interaction between the single-walled carbon nanotube (SWCN) and the Mg (0001) surface have been reported. It was found that the charge transfer from metal surfaces to the nanotubes takes place depending on both the electronic structures of the nanotubes and the work functions of the metal surfaces. The stable geometries for the nanotube between two consecutive objectives with C-Mg chemical bonds formed. The interaction energy in the most stable geometry is found to be CNT’s structural dependence. Concerning the electronic properties, the most stable structure showed a decrease in the density of states near the Fermi level due to the formation of C-Mg bonds enhancing the metallic character of the nanotube by the contact with the surface. The nature of the nanotube-interface interaction for nanotubes of larger diameters has been also discussed based on the calculated bond order.

Abstract: Gas tungsten arc (GTA) surface modification process was used to deposit SiC particles and aluminum alloy powders on the surface of magnesium alloy AZ31. This method is an effective technique in producing a high performance composite layer. This process result notable grain refinement in the GTA surface modified composite layer. The hardness and wear resistance of the GTA surface modified composite layer are superior to that of as-received magnesium alloy AZ31. The hardness values and wear resistance of GTA surface modified composite layer depend on the GTA process parameters and the SiC particles powder concentration and distribution. The optimum processing parameters for the formation of a homogeneous crack/defect-free and grain refinement microstructure were established.

Abstract: Intermediate phase growth in Mg-Al diffusion couples were studied with different intensity of a strong static magnetic field from 0 to 10 Tesla. Thickness measurement of the intermediate phases (Mg17Al12 and Al3Mg2) shows that with the increasing of magnetic field intensity, the growth rate of both intermediate phases is retarded. The decrease of the phase growth rate is ascribed to the suppressed Al, Mg atom interdiffusion in the diffusion couple under the static magnetic field. It is also found that the orientation relationship between couple interface and magnetic field direction has no influence on the growth of intermediate phases.

Abstract: The low frequency damping capacities of commercial cast AZ91D, squeeze cast AZ91D alloy and SiCw/AZ91D composite were studied using dynamic mechanical analyzer (DMA). The obtained strain amplitude dependent damping could be divided into two regions. In the region of small strain amplitude, the damping capacity was independent of the amplitude. While at high strain region, the damping capacity increased rapidly with increasing of strain amplitude. The G-L dislocation model was used to explain the damping capacity, and the differences of the distance between the weak and strong pinning points were discussed. The microstructures of the alloys and composites were observed and coincided with the analysis results according to G-L dislocation model.

Abstract: The fabrication processing, mechanical properties and fracture characters of SiCp/AZ91 magnesium matrix composites fabricated by squeeze casting were investigated. The SiC particles with different diameters (5μm, 20μm and 50μm) were employed as the reinforcement in the composites, the volume fraction of them was 50% in all cases. Experimental results showed that when the size of SiC particle decreased, the tensile properties of the composite increased. The tensile properties of SiCp/AZ91 composite with small particles are controlled by the properties of matrix alloy and the strength of the interface between the matrix and reinforcements, but the composites reinforced by large particles are controlled by the fracture of the particles.