This is the 1st progressive report on the growth twin crystals in aluminum and aluminum-base alloys, and describes the morphology of them.
A growth twin crystals in cast aluminum is found in the form of thin plate 30100μ in thickness in which a planar twin plane lies between both boundary surgaces. It originates near the cooling end of the cast block and grows in the direction parallel but opposite to the heat flow, accompanying multiplication or paralleled piling of new growth twin crystals. The (111) planes conjugate the twin plane and facted (100) planes grow at an angle 54.7° from the twin plane. It is therefore determined that prefered growth occurs on the (112) plane macroscopically.
The growth twin dendrite in multi-phase alloys such as aluminum-magnesium alloy has a similar crystallographic orientation. Both the columnar and growth twin crystals have similar dislocation density Dislocations and/or faults, however are dispersed in the former homogeneously, while they are concentrated in the latter on the twin plane. Other features of the growth twin crystal include crystallographic stability at elevated temperature normal segregation of solutes such as magnesium and lesser coring.

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This is the 2nd proqressine report on the growth twin crystals in aluminum and aluminum-base alloys. A theory of origin and multiplication of the growth twin crystals is proposed in inductively from various aspects of originating and multiplicating behaviors.
The (100) facets grow preferentially, in general in the direction opposite to the heat flow during unidirectional solidification of aluminum and aluminum-base alloys. If the preference is disordered by any way such as introducing other solute elements and oscillating the freezing metal, and more of the (112) facets grow in the direction opposite to the heat flow at a deviating angle within 10° degrees two-dimensional nucleation occurrs for growth twinning on the interface growing in such an orientation. The Base crystal grows continuously into the crystallographic lattice which constitutes an either side of the twin plane in the growth twin crystals to be originated.
The two-dimensional nuclei are generated at discontinuities of the crystallographic lattice such as stacking faults, grain boundaries, porosities and inclusions. This principle is substantially applicable to produce growth twin crystals in cast aluminum and aluminum-base alloys.
Both origination and multiplication are attributed to the same cause. The multiplication occurs on the growing interface of the growth twin crystal-neither on columnar nor equi-axed crystals.

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These investingations were undertaken concerning the effects of the ratio of width/thickness in reduced section of sheet-metal tension specimens on the tensile properties of aluminum alloy designated as 5052-0. The dimensions of the specimens for these tests were determined as follows. The width of grip sections was 1.41.5 times and the radius of fillets was 1.01.2 times as large as the width of reduced section.
The principal results obtained were as follows.
1) The size and shape of the test specimens used had little effects on the proof stress observed.
2) The tensile strength was very slightly increased with the increase in the ratio of width thickness. However, the effect was so little that the strength would substantially be unchanged independent of the size and shape of the specimens used.
3) The curve representing the relation between δ and L₀/√S₀ (in which δ: elongation percentage, L₀: gauge length, and S₀ : cross-sectional area of specimens) was very likely to be horizontal for the values of L₀/√S₀≥10, and the values of δ for L₀/√S₀≥10 were almost indifferent to the size and shape of the specimens used.
Accordingly, the gauge length of the sheet-metal tensicn specimens would preferable be determined in the range of L₀/√S₀≥10.
4) The type of fracture was changed at about width/thickness =6. The shearing of fracture appeared in the direction of plate thickness, when the ratio was less than 6, and in the direction of plate width when the ratio was more than 6.

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The effects of the excess of Si and Mg over the composition of Mg₂Si on the ageing behavior of Al-Mg-Si alloys were studied by measuring specific heat and hardness.
The principal results of experiments were obtained as follows.
(1) The heat was generated in two steps during heating of Al-Mg-Si alloys containing excess of Si over Mg₂Si composition, while it was genrated in one step for the alloys containing excess of Mg.
(2) When the alloys had been subjected to pre-ageing, the two-step heat generation was changed to one-step, and the temperature of starting the heat generation was so lowered that the temperature range of the generation was wider.

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The high temperature creep characteristics of dilute aluminum base alloys containing as solute copper, magnesium, silicon and germanium have been investigated with particular emphasis on the activation energy for creep. The activation energies for creep are about 36kcal/mol for all alloys in the temperature range from 250°C to 300°C, and they gradually decrease as the temperature is decreased from 250°C to 200°C.
The measurements of micro-vickers hardness for the specimens subjected to steady state creep show that the larger the difference in size between a solute atom and a solvent atom, the higher the micro-vickers hardness with an exception of Al-Si alloy. These results can be interpreted by the dragging motion of solute atmospheres around the jogs in screw dislocations.

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