The effect of the addition of Be and Sc on the microstructure and mechanical properties of A357 alloy were systematically investigated. The results show that the addition of small amounts of Be and Sc could change the acicular structure of iron-bearing intermetallic compounds to harmless compact Al-Fe-Si and Sc-Fe iron-bearing intermetallic compounds. Compact iron-bearing intermetallic compounds could improve fluidity, causing a reduction in interdendritic shrinkage during solidification. The addition of 0.05 wt % Be enhanced the quality index of the A357 alloy by 11% and increased the notch-yield ratio of fracture toughness by 4.5%. In contrast, the addition of 0.05 wt % Sc increased the quality index and the notch to yield ratio of fracture toughness up to 17% and 9%, respectively. Therefore, the microstructure and mechanical properties of the A357 alloy could be improved by substituting Be with Sc.
The principal purpose of this research was to evaluate the effects of Zr on the microstructure and thermal stability of an A357 alloy that has been subjected to an aging treatment (T6) and thermal exposure (250 °C). The results show that the addition of Zr had a significant influence on the refinement of the grain size, which enhanced the hardness and tensile strength of the A357 alloy under the T6 condition. During thermal exposure at 250 °C, the rodlike metastable bÕ-Mg 2 Si precipitates transformed into coarse equilibrium phase b-Mg 2 Si precipitates, resulting in a significant drop in the hardness and tensile strength of the T6 heat-treated A357 alloy. However, after thermal exposure, coherent, finely dispersed Al 3 Zr precipitates were found to be formed in the T6 heat-treated A357 alloy. The addition of 0.1% Zr played a critical role in improving the high-temperature strength. Consequently, the A357 alloy with the addition of Zr demonstrated better mechanical properties at room temperature and high temperature than the alloy without Zr, in terms of both microstructure and thermal stability.
With the discrimination in view made by other authors between the materially demonstratable and often visible anodic layer and the one acting as the dielectric-the "active" layer-of the electrolytic condenser, experimental evidence is presented indicating that essentially both layers are identical. It is shown, on the one hand, how "pure active layers" can be produced, composed of nothing but the dielectric component, and on the other hand, that the indicated discrimination of the former investigators is due to the inclusion in the "compound layers" used by them of essentially avoidable, non-dielectric components due to purely accidental features of their formation-features which, with the proper knowledge, may easily be eliminated in the experiment.A systematic connection of the present work with the organization hypothesis that has been advanced in a previous papers is established. The hydratability of different layers is discussed as one of their basic characteristics and a suggestion of their molecular structure is offered.The function of capacity versus formation voltage is found to correspond very nearly to a rectangular hyperbolic relation, and this necessarily follows from our conception of the nature and stratified structure of the layer.Incidentally, the relation between the resistance of the electrolyte and the breakdown voltage is broadly outlined, and also how the breakdown voltage is affected by changing the solvent of the electrolyte. An explanation of these facts is suggested.
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