Directional properties in polycrystalline metals are resulted from crystallographic factors which are also called preferred orientations, or mechanical factors such as elongated inclusions, segregation, cavities, primary crystals, elongated crystal grain form, etc.
This paper describes the effects of preheating on directional properties concerning mechanical properties and stress corrosion cracking of Al-Zn-Mg alloy thick plates, and the factors affecting these directional properties were also discussed.
The results obtained were as follows:
(1) The directional properties concerning tensile strength in 3 main directions (L, LT, and ST) were little in variation. The tensile strengths in the directions at an angle of 45°C to the main directions were lower than those in the main directions when the material was preheated at lower temperatures. However, the variation of these directional properties was less with the rise of preheatting temperature. The variation of directional properties was explained by crystallographic factors.
(2) The elongation was largest in the direction at the angle of 45°C to L and LT, and was gradually decreased with the change of direction toward L, LT or ST; it was smallest in ST direction. The elongations in these directions were increased with the rise of preheating temperature. These directional properties were explained by the combination of crystallographic and mechanical factors.
(3) The notch tensile strength was greatest in L direction and was gradually decreased with the change of direction from L to LT or ST; it was least in ST direction. The strength was decreased in L or LT direction, but was increased in ST direction with the rise of preheating temperature. These directional properties were explained by crystal grain forms in mechanical factors.
(4) The stress corrosion cracking resistance was lowest in ST direction and was gradually improved with the change of direction from ST to LT or L; it was highest in L direction. These directional properties were explained by crystal grain forms in mechanical factors.
(5) High stress corrosion cracking resistance was obtained in the material having subgrains and small, disperesed, and insolutble particles. The resistance was decreased with the rise of preheting temperature, because these structures were destroyed by preheating.
(6) The shear crack resistance was decreased with the rise of preheating temperature.

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This study was undertaken to investigate the precipitation phenomena during recrystallization of supersaturated and deformed Al-Mn alloys.
Specimens used were Al-1.34wt%Mn and Al-1.29wt%Mn-0.05wt%Si alloys. They were cold-rolled after solution treatment at 640°C, and were heated at several temperatures of 300600°C. Experiments were carried out by measurements of hardness and electrical resistivity and electron microscopy.
The results obtained were summarized as follows:
(1) Precipitation of manganese was accelerated by cold working. This effect was particularly marked when the specimen was anncaled at temperatures not higher than 400°C.
(2) At lower temperatures(≤400°C), precipitation process reached near the equilibrium state before the end of recrystallization process. Therefore, the nucleation and growth occurred in dislocations or dislocation cell structures (subboundaries). Therefore, the acceleration of precipitation would be due to the easier nucleation in these lattice defects and easier growth by pipe diffusion.
(3) At higher temperatures (≥450°C), precipitation occurred after the end of recrystallization.In this case, the nucleation took place also in the lattice defects, but the growth occurred in the recrystallized matrix. Therefore, the acceleration of nucleation was only due to the easier nucleation.
(4) The addition of 0.05wt%Si accelerated the precipitation process of deformed Al-Mn alloys and made precipitates finely distributed. This acceleration was supposed to be related with the retardation of recrystallization due to the finely distributed precipitates.
(5) Almost all the precipitates were identified as Al₆Mn in the both alloys. However, Al₆Mn precipitates were in globular form at lower temperatures and rectangular thin plates at higher temperatures.It was the first identification ever experienced in the world that the rectangular thin plates of Al₆Mn precipitates were observed in the from of rectangular thin plates.
(6) The crystallographic relation between the rectangular plates and aluminum matrix was found to be <110>Al//<001>Al₆Mn and {111}Al//{110} Al₆Mn and their habit planes were supposed to be{111}Al.
The rectangular plates seemed to be coherent with aluminum matrix at the earlier stage of precipitation.

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This study was conducted to confirm the effects of metal flowlne on the strength of die castings, which has been considered to be strong in the direction parallel to the flowline and weak in the direction normal to that.
As the results of analysis of variance, the effects of metal flowline on the directional dependence of strength were not observed in Al-si-Cu alloy(JIS ADC12)die castings produced by mass production method.
The cause of the above facts was examined and the following results were obtained.
(1) The metal flowline patterns resulted from the difference in the solidification structure. Bright parts were rich in primary α-crystals and drak parts were rich in eutecic silicon. Its thickness ranged from several μ to 50 μ.
(2) Preferred orientation of crystals was not observed on the surface having metal flowline patterns;nor was in the inner parts. The degree of orientation was found to be random.
(3) Therefore, the anisotropy of strength was studied by orienting the α-phase in the heat flow direction by unidirectional solidification of the alloy;but it was not found even under such conditions.
(4) The strength of die castings depended upon porosity and conditions for cooling of dies. Therefore, it was concluded that the effects of metal flowline on the directional dependence of strength are out of the question.

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The transition of solid-liquid interface morphology and redistributing behavior of solutes during unidirectional freezing of aluminum alloys were investigated with respect to temperature gradient (G), freezing rate (R), and initial concentration of the solute (C₀). The specimens used were Al-Fe, Al-Zn, and Al-Mn alloys having distribution coefficients (k) of less than 1 and Al-Cr alloys having the coefficient (k) of more than 1.
The critical condition for transition of interface morphology from smooth plane to irregular cell having depressions, was governed by the ratio of G/RC₀. It was found that the ratio for transition was extremely high in Al-Fe alloy and was low in Al-Mn and Al-Cr alloys.
The increase in concentration of solute at local segregation was not confirmed with the transition of interface morphology. The solute which had been condensed during freezing on the solid-liquid interface tended to increase the area of local interfacial segregation region according to the degree of constitutional undercooling.
Cell boundaries parallel to the growth direction were formed by grooves of cell nodes. The concentration of the solute, which had been in liquid state on decantation, was equal to that of the nodes on the interface. The variation in the concentration was not observed at places far away from the solid-liquid interface. However, discontinuous change of concentration was observed on completely solidified grooves. In Al-Fe alloys, the concentration of completely solidified solute on cell boundaries was higher than that on grooves due to the crystallization of FeAl₃. Whereas, reverse results were obtained in Al-Zn and Al-Mn alloys due to the dissolution of the solute. In Al-Cr alloy, the concentation of solute on the grooves was lower than that at cell center and extreme variation of concentration was not observed even when grooves were completely solidified.

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After Al-10%Si alloys were cast in a mould heated at 500°C, they were treated in two ways. Some of them were held in a mould at 500°C for 0.513hrs. Others were quenched in water immediately after solidification and reheated to 500°C and held at that lemperature for 113hrs. The relation between the impact strength and the structures of alloys thus treated was studied by means of Charpy impact tests and metollographic observations.
The following results were obtained:
(1) The size and distribution of eutectic silicon crystals were markedly affected by heating process after casting. After Al-10%Si alloys were cast in a mould heated at 500°C constant and were held there at the same temperature for a long time, there occurred little change in configuration of eutectic silicon crystals during holding, which were distributed in acicular or thin tabular form. As the results of Charpy impact tests, these alloys had little impact strength, which was hardly changed during the further holding.
However, when the alloys were quenched in water immediately after solidification and reheated to 500°C, the configuration in eutectic silicon crystals was gradually changed from acicular to spheroidal form durinng the holding at 500°C.
(2) When the alloys had previously been quenched to room temperature after casting, and then held at 500°C, the shape of eutectic silicon cry stals was converted into spheroidal form and the impact strength was greatly increased.
The difference in impact strength of these alloys would be attributed to the change in configuration of eutectic silicon crystals which may depend on their previous heat history, not on their high temperature heat treatment.
(3) In Al-Si alloys modified by the addition of metallic sodium, the configuration in eutectic silicon crystals showed almost the same behavior as that of unmodified alloys.

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Experiments were conducted to study the effects of distribution of solute elements on the mechanical properties of solidified weld metal in Al-4.5%Mg and Al-4%Zn-2%Mg alloys.
The mechanical properties of welds were more deteriorated with the increase of welding heat input. After homogenizing, tensile strength and hardness of the deposited metal were increased on the whole; but Charpy impact value only showed a reverse result. However, both of the tensile strength and impact value still depended on the initial welding heat input or dendrite cell size even after homogenizing, but the hardness did not.
After the above treatment, principal solute elements such as Mg and Zn were almost homogenized, which led to the vanishing of their segregations on the dendrite cell boundaries; but their concentrations in the cell matrix were increased. However, the distribution of impurities of Fe and Si (particularly, Fe) remained in as welded state even after homogenzing.
It was clear from the above facts that the hardness of welds was markedly affected by the dispersion of the 2nd phases containing Mg or Zn on grain and dendrite cell boundaries and their concentrations in the cell matrix. Whereas, the tensile property and Charpy impact value, which will lead to rupture, would be affected by the distribution of Fe and Si as well as the above two factors.
The above facts were proved by the experimental results that the mechanical properties of welds and permanent mould castings were deteriorated with the increase of Fe and Si. The network of the 2nd phases containing Fe and Si on grain and dendrite cell boundaries seemed to promote the crack propagation in rupture.
However, the effects of Fe and Si were observed in only Al-4.5% Mg and Al-4%Zn-2%Mg alloys containing considerable amounts of Mg and (or) Zn as strengthening elements. Whereas, these effects were not observed in commercially pure aluminum, in which Fe and Si rather act as strengthening elements for mechanical properties.

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