The load-elongation diagram of a soft steel tested at the temperature of blue shortness indicates continuous serrations after yield point up to the breaking stage. Although this phenomenon has been widely investigated, no satisfactory cxplanation has yet been given. Moreover, such a serrated deformation is not peculiar for a low carbon steel, as it is observable in some ferrous and non-ferrous alloys tested under a suitable condition. In order to contribute some light for this problem, the present author has studied it with carbon steels of various compositions and structures, some special steels, single cr_??_ stals of iron, duralumin, brass, copper, nickel, aluminium and zinc at temperatures ranging from the liquid nitrogen to the red heat. From these experiments two cases are classified for the serrated elongation. The one case is that when the materials having, to a certain extent, impurities or structural flaws are tested at a proper temperature and under a slow rate, if possible. The other is observable when the metals of high purity are tested at a rate as quickly as possible. These results are explained as follows:- In the fomer case the crystal grains are temporarily brought to an unstable state, by concentrated stress due to notch effect and in the latter case they are brought successively to an unstable state by overstress due to rapid loading and followed by yielding.

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Soaking the annealed Al-Cu alloy or duralumin in the nitre-bath heated at 540° or 500° respectively, the solution-velocities of various precipitates in the alloys have been determined rontgenographically. The effect of the rate of dissolution of the precipitates on the aging properties of the alloys has also been investigated. The results obtained may be summarised as follows:
(1) The dissolution of CuAl₂ at 540° in aluminium takes place at first very rapidly; for instance, it is 80% with the 3 minutes-soaking and nearly 90% with the 10 minutes-soaking.
Although no marked difference in hardness of the alloys after aging has been detected, the alloys soaked for a short time in the nitre-bath showed the tendency to harden rapidly during the aging, compared with those soaked for a longer time.
(2) In the case of duralumin, the solution-velocities of various precipitates, namely, CuAl₂, Mg₂Si, Al₁₃ Cu₇Mg₈, AlMn₆, etc., seemed to differ with each other; it is certain that the solution-velocity of Mg₂Si is smaller than that of CuAl₂.
In order to dissolve the precipitates almost completely into a solid solution, the duralumin should be soaked at least for 20 minutes at 500_??_510°

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Following Examinations were carried out.
(1) Change of Tensile Properties of the Billet in Container under Extruding Process.
(2) Relation between Tensile Properties and Deformation by Extrusion, in the Range of large Areal Reduction.
(3) Effect of Forging on the Billet before Extrusion.
(4) Effect of Drawing or Forging Deformation on the extruded Rod.
(5) Change of Tensile Properties of extruded Rod by Heat-treatment.
(6) Xray Examination for the Crystalline Structure of extruded Rod.
On the basis of these experiments, a consideration was made on the peculiar strength of extruded rod. Generally speaking, the strength of heat-treated alloys depend mainly on the crystalline structure and the interatomic configuration of constituent atoms in crystal grains. The latter can hardly explains the results of the present experiment. On the other hand, the micro-examination in the portion of an extruded rod, where the peculiar strength exists, has shown an irregularity of grain boundary, and it changes into a normal structure with the heat-treatment after increasing deformation by forging or drawing, the peculiar strength also diminishes by the same treatment. Similar inclination can be noticed in the Xray examination of the above specimens. The main cause of the peculiar strength of extruded rod has been attributed to the irregularity of the grain boundary due to severe deformation in the course extruding process.

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The Al side or corner of the equilibrium diagrams of Al-Ti and Al-Fe-Ti alloys was studied by thermal analysis, and solubility limits of Ti and Fe in liquid Al at various temperatures were determined.
In the Al-Ti system, there is a peritectic point at 0.05% Ti and at 665°. In the equilibrium diagram of Al-Fe-Ti system, there exist three primary surfaces, (Al), FeAl₃ and TiAl₃, and an invariant point at 658°, the reaction being
L+TiAl₃_??_FeAl₃+(Al).
The segregation of TiAl₃ in Al is also discussed.

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The result obtained are summarized as follows: -Season Cracking always takes place along the Crystal boundaries of alloy, and hence stress alone is not the Cause of it. It does occur less in the air and water but are noticeable in Chloride aqueous solutions, such as brine water. Season Cracking does not occur in all the Mg-Al alloys: Alloys to be susceptible to season cracking must contain a certain amount of Mg, in other wards, it occurs in the alloys which are temper hardenable, except in the state which are quenched or tempered at temperatures heigher than 250°. By quenching and tempering, a structural change takes place with physical and chemical changes, which accompanies with precipitation of particles discernible under the microscope. These changes attain the maximum degree at a range of 175_??_200°, at which the season Cracking is also the greatest. The season cracking in Mg-Al alloys can be greatly lessened by adding Mn or Cr to them.

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The mechanism of disintegrations of crystal grains of 24 S type superduralumin into crystallites during tempering was studied by X-ray back reflection method using Cu K_α radiation. The spot due to reflection of characteristic ray becomes at first somewhat diffuse, showing the process of precipitation of compound being taken place, till about 200°, then the spot is elongated and becomes irregular form, showing the grain being disintegrated into crystallites. This continues till 350° and at this temperature the lattice constant almost coincides with that of pure Al. The orientations of crystallites do not differ more than few degrees to those of original crystal grains.
Next, the effect of Fe upon, the solubility of Cu in Al-Cu alloy was studied, and the solubility curves were determined. When Fe was added, the solubility of Cu at higher temperatures was much reduced, this having much bearings upon the age-hardening of superduralumin which was developed by Nishimura.

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