Advanced Materials Research Vols. 750-752

Abstract: Thermal compression tests of AZ61 magnesium alloy were performed at deformation temperature 25-400°C with strain rates ranged from 0.02 to 20 s-1, and the microstructure was studied. The conventional dynamic recrystallization (DRX) and shear zones were observed on grain boundaries at temperatures above 200°C. The shear zone and the temperature rise are considered to be responsible for the fracture of specimens. For the large internal stress concentration in the shear zones and the deformation incompatibility between matrix and shear zones, the fracture grew along with the shear zones and the failure occurred in the large deformation field of the matrix at the high strain rate 20 s-1 even at 400°C.

Abstract: Molecular dynamics (MD) simulation has been performed to explore the microstructure, thermodynamics and dynamics properties of liquid Fe-Ni alloy based upon two different embedded atom method (EAM) models. The calculated PCFs with two EAM models are good agreement with the experimental values. While the calculated Scc (q) of Bhatia-Thornton (B-T) structure factor (SF) shows different behavior: a sharp increasing and a small one at lower q from G. Bonnys model and Zhous model respectively. The mixing of enthalpy with G. Bonnys EAM is positive in the whole concentration range. While the different mixing behavior with a slightly negative mixing of enthalpy based on Zhous model, which is consistent with the experimental results, is observed. Density and diffusion coefficients of liquid Fe-Ni as a function of composition show the same tendency based on both G. Bonnys model and Zhous model. In this work, Fe-Ni melts show different mixing behavior based on the two different EAM models.

Abstract: Magnesium alloys as the emerging commercial metal structure material have excellent specific properties and stability, which is more and more vital for researcher. This paper reviews the creep characteristics and the way to enhance the elevated temperature properties of Mg-Al based alloys. The current Mg-Al based alloys (including AZ, AM, AS, AE, etc.) are summarized. The future development direction is pointed.

Abstract: The effect of temperature on the mechanical properties and fracture surfaces of 93WNiFe alloy was investigated in tension with temperature ranges from 10 to 900 degrees. The ultimate strength declined gradually as the temperature increased, and the elongation increases below 400°C but decreases above it. The fracture surfaces changes from tungsten pellet cleavage to detachment of tungsten-matrix.The ultimate strength was influenced by the fracture mode, the elongation influenced by the the deformation of tungsten pellet and matrix.

Abstract: The effect of T6 heat treatment on dry sliding friction and wear characteristics of Al-20Si-5Cu under a fixed sliding speed of 200r/min and sliding time of 30mins was illustrated in this paper. The result reveals that T6 heat treatment can improve morphology of primary Si and Al₂Cu particles, enhance the hardness of the matrix. Wear rate increased with increasing of applied load. T6 heat treated samples have high wear resistance which is related to the improvement of microstructure, particularly with their increased hardness of matrix. But friction coefficient varies with heat treatment processes and has no sensitivity to applied loads, which fluctuates in a small range, so the friction coefficient can be considered to be stable. The wear mechanisms of T6 heat treated samples are also changed with increasing of applied load, from oxidative wear to fatigue wear.

Abstract: The α + β dual-phase titanium alloy, Ti-6Al-4V, was thermohydrogen processed with 0.1, 0.3 and 0.5 wt% hydrogen. Effect of hydrogenation on microstructure and mechanical properties of Ti-6Al-4V titanium alloy was systematically discussed. It was found that hydrogen stabled the β phase and leaded to the formation of α martensite as well as δ hydride in the hydrogenated titanium alloy. Mechanical properties of hydrogenated titanium alloy deteriorated with increasing hydrogenation content. The mechanism of hydrogen-induced microstructure/mechanical properties modification in Ti-6Al-4V alloy was elucidated.

Abstract: The grain refinement of 2-8 wt.% Y addition in as-cast Mg-Y binary alloys has been investigated. The results show that the microstructure of as-cast Mg-Y alloys consists of α-Mg matrix and Mg₂₄Y₅ phase. Mg₂₄Y₅ can become the effective nucleation core of α-Mg, and refine the grain size of the alloys. The ultimate tensile strength of as-cast Mg-5Y alloy is 180MPa at room temperature. Mg-5Y alloy can be a basis for developing light structural materials.

Abstract: The microstructure and mechanical properties of Mg-8Al-1Zn-3Ca magnesium alloy aged for different time are investigated. With the increase of aging time, the high melting point intermetallic compounds Al₂Ca and Al₄Ca are increased obviously in number and the phase of Mg₁₇Al₁₂ has a dramatic decrease in number. The longer aging time results in a significant segregation phenomenon. The second phase becomes coarsen, and mechanical properties decline.

Abstract: The Mg-12Gd-2Y-2Sm-0.5Zr (wt.%) alloy was prepared by induction melting. After solution and aging treatment, the microstructure and mechanical properties of alloy was investigated by optical microscope, XRD and tensile tests. The results show that the aged alloy is mainly composed by α-Mg matrix, Mg₂₄Y₅ and Mg₅Gd phase, and these precipitated phases distribute in the grain dispersively. The mechanical properties of alloy were tested at room temperature and 200-300°C.

Abstract: According to the design concept of multi-element high-entropy alloys, seven kinds of elements (Cr, Mn, Fe, Co, Ni, Cu and Si) were selected in this work to design a series of CoCrFeNiCuMnSi_x high entropy alloys. Metal power was melted by vacuum arc furnace. Cast microstructure and phase structure of the high entropy alloy were Characterized by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD). And then, hardness, wear resistance and corrosion resistance were tested. Phase structure of cast microstructure, the morphology of the microstructure and mechanical properties of the CoCrFeNiCuMnSi_x high entropy alloys were researched systematic in the condition of different content Si. The results show that the crystal structure is simple BCC structure. With the increasing Si content, the alloy cast structure changes from dendrite morphology to cellular morphology. It was Si content that plays an important role in increasing significantly the hardness of the alloy. The hardness of the maximum value reaches to HV985.