Various aluminum fluoride fluxing treatment were tried to achieve a practical process for demagging from molten aluminum alloys. The tried treatments included pure aluminum fluoride fluxing, aluminum fluoride-open-hearth fluxes mixtures fluxing, and aluminum fluoride fluxing followed by open-hearth fluxes fluxing. Fluxing with mixtures of aluminum fluoride and open-hearth fluxes at temperatures 760°C or above is the most effective. An effect of initial Mg concentration in aluminum alloys on demagging efficiency is determined. An antipollution demagging process using silica (U. S. Pat. 4, 097, 270) was also tested. It is not so applicable economically and has a low and unstable demagging efficiency.

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Fracture toughness of 7079 alloy was evaluated by double torsion bend test. The conventional hot-rolled 7079 plate shows the dimensional anistropy on fracture toughness. The thermomechanical processed 7079 plate is higher in fracture toughness and is lower in the anistropy on fracture toughness in conventional with the comparison hot-rolled plate. The interrelation between microstructure and fracture toughness is discussed on the basis of stereo-fractography.

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The toughness of 7075 and 7475 alloys was examined by tear tests using modified Kahn type specimens of 3mm in thickness. Alloy specimens were solution-treated at 470°C or 495°C, quenched, and were subjected to two-step aging (T73 treatment). verage values of UPE (energy necessary for crack propagation per unit area) are always higher in 7475 than in 7075, when heat-treated in the same way. Fine grained structure is significant for an increase of UPE values in both alloys. Measured individual values of UPE however show a marked fluctuation compared with that of pop-in strength or tear strength. The fluctuation of UPE values is considered to be mainly due to heterogeneous distribution of different kinds of constituent particles in specimens.

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Mechanical properties of fully aged 6061-type alloy, affected by Fe content ranging from 0.1 to 1.1wt%, were studied. Only a slight variation in hardness and tensile properties (ultimate tensile strength, 0.2% proof stress, elongation) was observed in the range of Fe≤0.7%. However, larger amount of Fe brought about harmful effect on the above properties. Tear resistance decreased monotonously with increasing of Fe content. These results could be explained, considering that coarse constituent particles containing Fe, Si, Cu, etc. increase in amount as Fe content increases, leading to the decrease of solute concentration in matrix.

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The Al-Zn eutectoid-base alloys having, equiaxed, initial grain sizes from 0.14 to 3.03μm were deformed in tension at temperatures from 213 to 523 K at different strain-rates. The following five deformation regions were found: a region where cavitation predominates and superplasticity is weak; a region where superplasticity arises; a conventional deformation region where the Hall-Petch relation holds; a transition region from the superplastic to the conventional region; a brittle fractural region. By partitioning these regions on temperature vs. grain size, and, tensile stress vs. grain size diagrams, deformation-mechanism maps were made, which could clearly show the extent of temperature, grain size and strain-rate or stress where the superplasticity arises. There exists a grainsize L_m where the tensile stress σ_uy takes a minimum value σ_m in a ultrafine grain region, in which the grain-size dependence of the stress was expressed as: σ_uy = aL^-1/2+bL = (σ_m/3)(2L^3/2_m+L^3/2)/L^1/2L_m, where a = (6.73γ_BG)^1/2 and b = (G/b){(εRT/AGbD₀)exp(U/RT)}^1/n, where γ_B is a surface energy of the cavity and the other symbols have conventional meanings. On the other hand, the Hall-Petch relation held in a coarse grain region.

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