Materials Science Forum Vols. 610-613

Abstract: The magnesium alloy sheets have poor plasticity and formability due to their strong (0002) basal texture. In this paper a new method, repeatedly unidirectional bending (RUB), was used to improve formability of the magnesium alloy sheets. The samples were deformed repeatedly by the unidirectional bending at room temperature and annealed. Firstly, RUB route which is the most infection to formability was investigated. There were two RUB route, single surface RUB and reserve surface RUB. The result showed that better formability can be obtained by the reserve surface RUB. Focused on the development of formability of magnesium alloy sheet, the technological parameters, such as RUB passes, radius of support, annealing temperature and holding time, were determined by orthogonal experiment,and hence the optimal RUB process was acquired. Mechanical property of the samples before and after RUB were characterized and compared. After RUB, (0002) basal textural component of cold rolled magnesium alloy sheet was weakened and σb, σ0.2 decreased obviously. The Erichsen values can be considerably enhanced from 3.53mm to around 6.0mm through RUB.The samples were deformed repeatedly by the unidirectional bending at room temperature and annealed. Firstly, RUB route which is the most infection to formability was investigated. There were two RUB route, single surface RUB and

Abstract: Stronger (0001) basal plane textures mainly include two types: and in AZ31 magnesium alloy thin sheet were formed after hot-rolling. The texture types of hot-rolled AZ31 magnesium alloy thin sheet after annealing at 523K and 673K respectively were as same as that of hot-rolled thin sheet without annealing, but texture intensities became weaker, especially after annealing at 673K. The strong texture of hot-rolled thin sheet caused anisotropy of mechanical properties (tensile strength b, yield strength s and elongation ) significantly , and the anisotropy reduced with the decrease of texture intensity after annealing. Besides texture, the grain shape also effects anisotropy of mechanical properties. The anisotropy becames more significantly with the increase of relative difference of grain diameter between transverse and longitudinal directions.

Abstract: The as-cast microstructures and mechanical properties of Mg-3Ce-1.2Mn-0.9Sc and Mg-3Ce-1.2Mn-1Zn magnesium alloys were investigated and compared. The results indicate that the as-cast microstructure of Mg-3Ce-1.2Mn-0.9Sc alloy was mainly composed of -Mg, Mg12Ce and Mn2Sc phases, and that the as-cast microstructure of Mg-3Ce-1.2Mn-1Zn alloy was mainly composed of -Mg, Mg12Ce and MgZn phases. In addition, the as-cast tensile and creep properties of Mg-3Ce-1.2Mn-0.9Sc alloy were higher than that of the Mg-3Ce-1.2Mn-1Zn alloy. The difference of the two alloys in as-cast tensile and creep properties may be related to the initial microstructures of the two alloys.

Abstract: The hot spot forming tendency during solidification of AZ91D magnesium alloy in permanent mould casting with the dies of different wall thickness via numerical simulation with Anycasting software was studied in the present paper. The experimental results showed that in a single cycle casting the increase in the thickness enhanced the cooling ability of the mould and promoted balanced solidification in a certain degree, while in multi-cycle casting, the thickened die-wall gradually lose its localized chilling effect. In contrast, the die with a decreased wall thickness in a certain range was easier to achieve the desired solidification balance.

Abstract: High quality magnesium casting depends significantly on the purification of its alloy melt. However, it is very difficult to obtain high-quality magnesium alloy melt due to its high reactivity and its tendency of combustion. The fluxing processing, a traditional purification method for magnesium melt, not only bears the risk of flux inclusions but also is facing more and more environmental pressure today. Therefore, the effective substitutes for fluxing processing, such as physical filtering method, are paid more attention recently. In this paper, the effects of technological conditions including the pore size of stainless steel mesh and the filtering temperature on the purification degree of AZ91 alloy melt were investigated in the mesh filtering processing, in which 2 wt.% calcium was added into the melt in order to obtaining ignition-proof property. The results indicated that mesh filtering processing could improve the purification degree markedly, and the purification degree increased with the increase of filtering temperature properly or the decreased of pore size of mesh. However, too high filtering temperature would lead to the increasing of the tendency of oxidation and combustion, and too small pore size would decrease the filtering ability of mesh which would lead to the interrupting of purification operation.

Abstract: Mg scrap is notorious for the high cost and serious pollution of its recycling process due to the good wettability and similar density of Mg melt to its solid inclusions. To support the sustainable growth of Mg industry and application, intensive effort has been contributed to the development high efficiency, flux-free purification techniques for Mg scrap recycling. In the present study, the purification of Mg scrap melt via filtration was theoretically analyzed by multi-phase fluid hydrodynamics. The relationships between the nozzle size in the filtration medium, melt penetrating-through speed and other filtration parameters were formulated. To provide a guideline to filtration engineering, the influence of processing parameters on the filtering efficiency were discussed.

Abstract: In present work, trace elements Sr and Nd were added into AZ91-1wt%Si alloys. The alloys were cast into a permanent mould and then machined into test bars. The microstructure and mechanical properties at room temperature of the specimens were investigated. Results showed that complicated Chinese script Mg2Si phase decreased in size with the increase of Sr addition. When Sr addition increased to 0.1wt%, the Mg2Si phase was changed from Chinese script shape into uniform polygon shape completely. At the same time, mechanical properties improved due to the morphology modification of the Mg2Si phase. An intermetallic compound containing Mg, Al, Nd and Si was found when Nd was added to the alloy. Remarkable modification on the shape and distribution of the Mg2Si phase was observed because of the intermetallic compound, which leads to a great change in mechanical properties. The grain refinement mechanism of Sr and Nd elements on the Mg2Si phase was discussed.

Abstract: The samples with different strontium contents of AE42 magnesium alloy were prepared. The metalloscope and electronic microscope and XRD were used to characterize the microstructure and composition of the samples. The elevated temperature mechanical properties of the samples were tested and the strontium phases in the AE42 and their influence to the mechanical properties analyzed. The results showed that the main strontium phase in the AE42 was Al4Sr. Al4Sr pinned the crystal boundary of magnesium matrix and hindered dislocation climbing and sliding through the crystal boundary effectively. As a result, the crystal axial range was reduced and the crystal grain refined, and hence the creep resistance increased.

Abstract: The species and shapes of impurities in magnesium alloy melt were studied. Floatation Refining method of Magnesium Alloys melt and eduction dynamics analysis were used to judge the floatation condition of gas bubble with MgO impurity. Models of floatation eduction were established to study the dynamics relationship of weight, drag and buoyancy. The relation curve between refining gas bubble radius and floating up rate was established. The choice method of gas bubble radius was provided and a practical process scheme proposed for floatation refining of magnesium alloys melt.

Abstract: In order to study the influence of die structures and process parameters on ECAE for wrought magnesium alloy AZ31 and obtain optimized process parameters, the three-dimension(3D) new geometric models with different corner angles (90o,120o,135o) and with or without inner round fillets in the bottom die were designed. The simulation results showed that the loads of top dies declined mainly with the corner angles increasing and inner round fillets of the bottom dies manufactured, the bottom die with inner round corner and the corner angle of 90o was propitious to improve the plasticity and deformation homogeneity of the billets.