Advanced Materials Research Vols. 881-883

Abstract: Based on the fatigue crack propagation experiments did by A.-L. Gloanec et al., the fatigue crack propagation rates of TiAl alloy of two processing routes, namely casting and PM, and stress ratios had been tested, in order to find out the effects of microstructure and stress ratio. An improved fatigue crack propagation formula for region Ⅱ (the expansion region) was derived according to Paris formula. The specific values of the constants in the formula were calculated. Fatigue crack propagation resistance of nearly fully lamellar microstructure is superior to that of equiaxed γ grain. The experimental results present that both microstructure and stress ratio has a significant influence on fatigue crack growth rate.

Abstract: The motion of interstitial atoms (one of the point defects) in material is random under certain temperature. However, the diffusion of interstitial atoms has priority along some certain directions to the others, so it is necessary to reveal the phenomenon (the phenomenon also can be called anisotropic). In order to illustrate the anisotropic and reveal the magnitude of probability of the micro crack formation along crystal axes, some formulae derived from former literatures have been adopted, and the values of diffusion probability and diffusivity of interstitial atoms-Ti or Al along 〈110〉and〈100〉have been calculated. The conclusion that the diffusion of interstitial atoms along different crystal axis has different diffusivity is verified by the comparison of the results of calculations.

Abstract: The effect of complex adding Nd and Sm elements (0.8~4wt %) on the microstructures and properties of AZ81 magnesium alloy were studied. The results show that the microstructure of the alloy was refined obviously after complex adding Sm and Nd elements. The grain sizes were declined from 98μm to 77μm, and β(Mg17Al12) phases which had a broken network distribution in alloy were decreased. At room temperature, when the addition of Sm and Nd increased to 1.5%, 0.9% respectively, the alloy had a tensile strength of 283MPa which was 10.55% higher than the base alloy. At the temperature150°Cand175°C, the tensile strength of the AZ81 alloy with 1.0% Sm and 0.6% Nd reached 208.8MPa and 176.5Mpa respectively which was 10.01% and 8.37% higher than the base alloy respectively.

Abstract: The reaction process of synthesis of Al₄SiC₄ from Al, Si and graphite powders and the effects of Y₂O₃ on synthesis and microstructure of Al₄SiC₄ were investigated in this paper. The results show that no substantial changes in the formation of Al₄SiC₄ content with or without addition of Y₂O₃. The addition of Y₂O₃ to Al, Si and carbon powder mixtures was found to be effective for obtaining tabular grains of Al₄SiC₄. Conversely, Al₄SiC₄ grains existed as irregular granules without addition of Y₂O₃.

Abstract: The solution treatment of 6063 aluminum alloy was carried out and the influences of solution process on microstructure, strength, hardness, and electrical resistivity of 6063 aluminum alloy was analyzed. The result shows that the suitable solution treatment can improve alloy solution-degree fully, meanwhile the changes of electrical resistivity of alloy tend to be balanced. The suitable solution process for 6063 aluminum alloy is solution-treated at 520°C for 3.5h, and the strength and hardness of alloy can be enhanced extremely after aging-treatment at 200°C for 5h.

Abstract: Based on the first-principles pseudo-potential plane wave method, the effect of Cr addition on the microstructure of NiTi alloys are characterized and assessed with the formation enthalpy (ΔH), binding energy (ΔE) and density of states (DOS) distribution of NiTi (Cr) crystals. The results show that the binding energy of NiTi (CrNi) is slightly smaller than that of NiTi (CrTi), but the formation enthalpy of NiTi (CrTi) is much smaller than that of NiTi (CrNi).So the Ms of NiTi alloy could be decreased by the addition of ratio for Ni/Ti. And the electronic microstucture of NiTi (CrNi) alloy are also illustrated clearly.

Abstract: The thermal fatigue behaviors of traditional Al-Si-Mg casting alloy and optimized Al-Si-Mg casting alloys at different thermal fatigue temperatures were investigated. Fatigue cracking appeared on the surface of traditional Al-Si-Mg alloy after 450 thermal cycles at 300 °C thermal fatigue temperature. However, the fatigue cracking was not found on the surface of optimized Al-Si-Mg alloy at the limited thermal fatigue cycles (less than 4450 times). Moreover, the optimized Al-Si-Mg alloy only occurred to elastic deformation and could not emerge in irreversible deformation. The grain refinement in the optimized Al-Si-Mg alloy could make the thermal fatigue cracking appeared much later and propagated much slowly. These results showed that the thermal fatigue resistance of optimized Al-Si-Mg alloy was superior to that of traditional Al-Si-Mg alloy.

Abstract: According to the principle of bubble floatation, purification of ZL114 aluminum casting alloy has been studied by blowing nitrogen gas into the ZL114A alloy melt through the porous plug which can produce dispersed micro bubbles. 5 samples have been taken at 0 min, 2 min, 4 min, 6 min, 8 min and 10 min, respectively, to measure the hydrogen content through HYSCAN II hydrogen tester. The experiments results show that the removing effect of hydrogen is remarkable. The hydrogen removing efficiency reaches 85.7% when blowing lasts 4 minutes. The rate of hydrogen removing begins to decrease from 4 minutes to 10 minutes; the hydrogen removing efficiency gets to the maximum after 8 minutes. The inclusions are also removed with the removal of hydrogen.

Abstract: A damage limit prediction model was built due to fracture failure problems of aluminum alloy plates. Based on the global plastic collapse of the entire cross-section containing the defect, the relationships of crack width and depth of fracturing 7075 aluminum alloy plates with either shallow crack or deep crack was analyzed by using reference stress method. The damage limit curves of 7075 aluminum alloy plates with crack was drew, and safety zone of crack propagation under corresponding bending load was confirmed. Then the experimental verification was carried out, results show that calculated results are in good agreement with the test results during the shallow crack stage, while in the deep crack stage experimental results are slightly less than calculated results.

Abstract: The Mg-12Gd-3Y-1Sm-0.5Zr (wt.%) alloy was prepared. After solution and aging treatment, the microstructure and mechanical properties of alloy was investigated. The results show that the experimental alloy is mainly composed by α-Mg matrix and Mg₅Gd, Mg₂₄Y₅, Mg₄₁Sm₅ phase. The experimental alloy has excellent creep properties at 200-300°C/50-70MPa.