Materials Science Forum Vols. 488-489

Abstract: Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.

Abstract: High-temperature tensile and fracture behaviors of as-extruded ZK60 alloy were investigated. It was evident from the experiments that with decreasing temperature and increasing strain rate, the 0.2% offset yield strength and ultimate tensile strength of the alloy increased while the elongation to failure decreased. The flowing stress of as-extruded ZK60 alloy during plastic deformation was proportioned to the reciprocal of temperature. At the initial strain rate of 5×10-4s-1, the calculated active energy at 300°C was about 93.4 kJ/mol.

Abstract: This paper investigates the microstructure, mechanical properties and creep behavior of Mg–Al–Ca alloys with different Ca content. SEM and EDAX analyses show that the dominant second phase in the as-cast Mg–Al–Ca alloys is Al2Ca, which distributes at the grain boundaries and disperses in the grain interior as well. Both the elevated tensile strength and the creep resistance of Mg–Al–Ca alloys obviously increased with increasing Ca at high temperature. TEM analyses reveal that finer Al2Ca particles with an average size of 0.02 µm precipitated dynamically during the creep process. Selected area electron diffraction (SAD) patterns show that the dynamic Al2Ca precipitates have a coherent interface with matrix as (0110) Mg // (220) Al2Ca, [2110] Mg // [112] Al2Ca. The strengthening mechanism of Mg–Al–Ca alloys at elevated temperature was discussed.

Abstract: In present work, Sr, Ca and Si elements were added into AZ91D and cast into a metallic mold. The influence of these elements on AZ91D magnesium alloy were studied systematically with the purpose of developing a new magnesium alloy with good mechanical properties at both room and high (150°C~200°C) temperature. Additionally, a simple method to qualitatively analyze the high-temperature creep performances of magnesium alloys was designed and implemented.

Abstract: Mechanical properties and high temperature deformation behavior of AZ31-0.84%Sb alloy have been studied. The results show that small additions of antimony to AZ31 alloy effectively enhanced the creep resistance and the ultimate tensile stress of the alloy at elevated temperature. One of the reasons for the improved high temperature properties is the high volume fraction (~20%) of the precipitates, as Mg3Sb2, which effectively hindered the movement of dislocations during the elevated temperature deformation. Considerable amounts of twins were formed during creep failure of AZ31-0.84%Sb alloy. Within the twins, many dislocation pile-ups were present on both basal and non-basal plane of magnesium matrix.

Abstract: The hot-rolled and extruded AZ31 specimens are subjected to tensile tests at room and elevated temperatures. At room temperature, the yield stress of the hot-rolled specimen is significantly higher than that of the extruded, the reason for which is related to the different textures developed in the two type specimens, as well as the different slip systems activated. At elevated temperatures, the strain rate sensitivity and the activation energy are obtained to characterize the deformation mechanism of the alloy during the temperature range of 423~573K.

Abstract: The poison’s ratio of plane plate samples taken from AM60 magnesium alloy was tested in this paper. A number of strain controlled fatigue experiments were also carried out on MTS to investigate the stress-strain behavior under different temperature conditions. The finite element analysis software ANSYS was employed to simulate impact process of shot blasting. Results indicated that at the specific temperature condition the residual stress and plastic strain increased with impact velocity increasing. At the specific impact velocity, residual stress reduced and plastic strain increased with temperature increment.

Abstract: Compressive behaviors of SiCw/AZ91composite and AZ91 alloy were investigated at temperatures from 423 K to 723 K and strain rates from 0.002 s-1 to 0.25 s-1. Microstructure evolutions after compressed at 623 K and 0.01 s-1 were observed by SEM and TEM. Results showed that compressive flow stress decreased with the increase of temperature; whiskers were broken and redistributed to the direction normal to the compression direction. At the initial stage of compression, dislocation sliding is the mainly deformation mode for the composite, while for AZ91 alloy, twining was the dominant mechanism.

Abstract: Galvanic corrosion is a particularly important form of corrosion for Mg alloys used in automobiles. Our research work focuses on corrosion protection using cost-effective Cr-free coatings. The top-tanking coatings are found to be effective in preventing general corrosion; some of these coatings are also good for reducing galvanic corrosion and stress corrosion. A practical approach for mitigating galvanic corrosion is to increase the electrolytic resistance between the coated steel and the Mg surfaces. This has been demonstrated in the case of a conversion coating plus a powder coat applied on the surface of a magnesium alloy and in the case of a thin Mylar isolation layer installed between the Mg and the steel surfaces.