Materials Science Forum Vols. 561-565

Abstract: The orientation changes during heating of extruded AZ31 were investigated using synchrotron Xrays by in-situ experiments. The as-extruded sample shows a strong <10.0>-fiber texture which is generally observed after round extrusion. The initial <10.0>-fiber texture, in which the <10.0> direction of the hexagonal crystallites is parallel to extrusion direction, starts to change to <11.0>- fiber component at 300 °C. The orientation change rate shows an exponential relation to the heating temperature and the soaking time. The microstructure observations, prior and post heat treatment, indicate that the texture changes occur mainly during grain growth.

Abstract: The wrought magnesium alloys AZ80 and ZK60 were extruded at 175°C ≤ T ≤ 350°C at an extrusion ratio of ER = 12. With decreasing extrusion temperatures a marked refinement in grain size was found for both alloys resulting in higher values of yield stress while UTS values were hardly affected. As opposed to AZ80, a marked yield stress differential between loading in tension and compression was observed in ZK60, this effect being explained by the differences in crystallographic texture.

Abstract: The latest research results on new types of magnesium alloys containing strontium or rare earth elements are reviewed. Special attentions are paid to the alloying design, microstructure and properties controlling, the influence of minor addition of Sr and RE on the microstructure and properties of existing magnesium alloys. Some new types of magnesium alloys containing Sr or RE are introduced and discussed.

Abstract: The lightest density of Mg has stimulated renewed interest in Mg based alloys for applications in the automotive, aerospace and communications industries. However, Mg in the pure form has relatively low strength, limited ductility and is susceptible to corrosion. Great efforts have been made to improve the mechanical properties of Mg alloys. Alloying Mg with other elements is one of the most important methods. An important class of Mg alloys is the Mg-Zn-RE system (RE = rare earth elements). In recent few decades, a series of new Mg-Zn-RE system alloys have been obtained, and detailed the structure and mechanical properties of the alloys. In this paper, the structure and mechanical properties of the Mg-Zn-RE alloys have been summarized. It showed that these alloys have high strength and they are prospected to be widely used in the future.

Abstract: Hydrogen evolution behavior of an Al-Mg-Si alloy affected by hydrogen embrittlement was investigated using a tensile testing machine equipped with quadruple mass spectrometer in an ultrahigh vacuum chamber. Plate type test pieces were solutionized at 540°C for 1h, quenched in water and then aged at 175°C for 8h or 240h. Some of the aged test pieces were pre-deformed in air with a relative humidity of 90% at a slow strain rate of 8.3x10-7s-1 to introduce hydrogen from the testing atmosphere. As a result of the tensile test with mass spectrometry, it was shown that hydrogen was highly evolved at the moment of fracture. The area fraction of intergranular fracture decreased when the aging condition was changed from peak-aged to over-aged, which was in agreement with the decrease in the amount of hydrogen evolved at the moment of fracture.

Abstract: Tensile properties and deformation-fracture behavior at temperatures ranging from 123K to 293K of a Ti-6Al-4V alloy sheet with a thickness of 1.5mm has been studied, and the effects of testing temperature, specimen orientation and heat-treatment were investigated. An increase in strength and a decrease in fracture strain were found with decreasing tension temperature, and the anisotropy in tensile properties was observed at room and cryogenic temperatures both in the annealed and solution treated and aged (STA) specimens. TEM examinations indicated that plastic deformation occurred within both α and β phases in the STA specimens testing at either room or cryogenic temperature. The dominant deformation mechanism varied from dislocation slip at room temperature to twinning at 123K. SEM observations showed that the amount of dimples and tearing grains on fractured surfaces of the specimens decreased as testing temperature was decreased.

Abstract: Plasma-enhanced ion beams are used for the surface modification of 2024 Al and 7075 Al alloy samples. The morphology of the treated surface of the samples is examined. The corrosion resistance and bending fatigue properties were measured on the treated and untreated samples. The effects of ion beam parameters are discussed. It is indicated that during the ion bombardment, craters are formed and surface melting is produced on the treated surfaces. The effects of ion beam bombardment are limited to the surface layer of samples. With the ion beam energies used in this study, improved corrosion resistance was obtained from the treated surfaces of the samples.

Abstract: The Air-acetylene Flame Atomic Absorption Spectrometry (FAAS) was used to measure Sr content in Mg-Sr Alloys. The experiment conditions including acetylene flow rate, measurement height, flame wavelength were studied and the disturbing factors were discussed. It was found that, as dissolution agent of alloys and LaCl3 as the deionization agent and flame wavelength being 460.7nm, the detection limits is 1.16mg/L and the relative standard deviations is less than 0.3% and the recovery rates of Sr is more than 95%. The advantages of this method were summarized as: high sensitivity and precision, low chemistry disruption, good selectivity, good recurrence characteristics of the measuring conditions. The method is suitable for the control analysis and sample-system analysis of determination Sr content in the Mg-Sr Master Alloys.

Abstract: In this study, it examined recycling of a Mg-Al-Ca based alloy by vacuum distillation. The vacuum distillation used a vacuum distillation apparatus and it evacuated a vacuum and heated the Mg-Al-Ca based alloy to less than 1Pa at 600°C. Condenser temperature changed it into 280-420°C and performed it. It melted and cast the magnesium condensate which I collected by the vacuum distillation and investigated corrosion resistance and mechanical properties. The condensation ratio increased so that condenser temperature was low. The quantity of zinc decreased so that condenser temperature was high. The quantity of calcium increased slightly so that condenser temperature was high. Most of the other elements did not mix it. The corrosion resistance of castings was good. The elongation of castings became bigger than commercial pure magnesium.