A testing method has been investigated to evaluate quantitatively the toughness of medium-strength aluminum alloys using sheet-type specimens. In this method, toughness was evaluated by the balance of the following two values; the resistance to crack initiation and the resistance to crack propagation, which were obtained by the static tear test at room temperature.
It was considered that notch strength was an index of the resistance to crack initiation. In this method, notch strength was defined by the maximum load in the load-deflection curve of the tear test. For the resistance to crack propagation, the slope of the load-deflection curve during crack propagation was considered as its index.
In the load-deflection curve, the toughness values are expressed as follows:
1) as an index of the resistance to crack initiation
Notch strength: σmax=Pmax/A(kg/mm₂)
Pmax: the maximum load of a load-deflection curve (kg)
A: net sectional area (sectional area at the notch) (mm₂)
2) as an index of the resistance to crack propagation
Unit slope=U. S.=Actual slope/A(kg/mm/mm₂)
Actual slope is the slope of the load-actual deflection curve during crack propagation. (kg/mm)
It was recognized that there existed correlations between σ_0.2 and (σmax)² and between (σmax)² and the U. S. value for about twenty commercial aluminum alloys with no defects. The relation between (σMax)² and σ_0.2, which was considered to show the resistance to crack initiation, was linear in the whole range. The relation between (σmax)² and the U. S. value, which showed the resistance to crack propagation, was linear only in some regions.

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A testing method was proposed, to evaluate the toughness of medium-strength aluminum alloys in the first report.
The toughness of these aluminum alloys was clearly shown to be evaluated with the U. S. value which was defined as the index of the tear resistance instead of the U. P. E. value.
In this report, the relation between the U. S. value and the U. P. E. value was examined. As a result of this investigation, we concluded as follows: the U. P. E. value was not sensitive enough in expressing quantitatively the toughness of the various aluminum alloys. Effects of specimen thickness on the toughness value were also examined experimentally and it was considered that the toughness value was hardly influenced by the specimen thickness if it was less than 10mm.

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Latent hardening in aluminum single crystals has been studied by measuring the flow stress on the secondary slip systems. Parent crystals were prestressed to various stress levels at room temperature. Secondary crystals oriented for the coplanar and intersecting slips were cut from a parent crystal and pulled at room temperature and 77°K.
Results obtained are as follows:
1) The shear stress-shear strain curve, the critical resolved shear stress (CRSS) and the work hardening rate in secondary crystals oriented for the coplanar slip are similar to those for the primary slip. While, in secondary crystals oriented for the intersecting slip, CRSS increases and the work hardening rate decreases compared with those in the parent crystal.
2) Slip lines in secondary crystals oriented for the primary and coplanar slips are fine and distributed uniformly, while those in the intersecting slip are coarse and concentrated.
3) In the coplanar slip, latent hardening is not recognized. In the intersecting slip, the following relations exist between the prestress τp and CRSS τl, τl(RT)=1.25τp(RT)+60 (g/mm²) τl(77)=1.5τp(RT)+100 (g/mm²) For the intersecting slip the dependence of CRSS on the slip system is not observed.
4) The latent hardening ratio in the intersecting slip is high when τp is relatively small and decreases to 1.2-1.4 at room temperature and 1.5-1.7 at 77°K with increasing τp.

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It is widely known that the rate of low temperature ageing of Al-Cu alloys was slowed down with a small addition of In. However, the mechanisms of the aging suppression phenomena in the Al-Cu-In alloy system are still unknown, and remain to be clarified. Then, the experiments to examine the phase constitutions near the Al corner of the Al-Cu-In system were carried out by means of thermal analysis, microscopic observation and X-ray diffraction analysis. Also, the measurements of electrical resistivity at the liquid-nitrogen temperature and the lattice parameter at room temperature were made to examine the limits of solid solubilities of copper in the α-phase at soution-treating temperatures in these alloys.
The results obtained are as follow:
1) It is found that the vertical section from θ (CuAl₂) to In in the Al-Cu-In alloy system constituted the pseudobinary phase diagram as in the θ-Sn and θ-Cd alloy systems.
2) Invariant reactions in the Al-θ-In ternary system are as follows: L₁_??_L₂+Al+θ monotecto-eutectic reaction at 541°C L₂_??_Al+θ+In eutectic reaction at 155°C
The monotecto-eutectic composition is about Al-27wt%Cu-15wt%In.
3) At various solution-treating temperatures (520, 500, 480 and 460°C), the solubilities of copper in the α-phase were little decreased with the addition of In as in the Al-Cu-Cd and Al-Cu-Sn ternary systems.

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