Chlorine, which is one of the effective gaseous fluxing agents, has widely been used for the degassing of aluminum and its alloys. As it is very poisonous, in practice, utmost caution must be given for its operation as well as perfectness of exhausters. Moreover, degassing by chlorine gives excessive loss of metals, especially a remarkable reduction of Mg content in aluminum alloys.
In recent days, it has been replaced by gaseous mixtures of N₂-Cl₂ as harmless degassing agents, which are attracting the public attention. Though it had previously been reported that the mixture of 10% chlorine in nitrogen was effective, systematic studies of this mixture have not yet been made. The present experiments were undertaken on the efficiencies of degassing by various mixtures of chlorine with nitrogen and on those by fluxes concurrently used in combination with the gaseous mixtures.
The following results were obtained.
(1) The degassing efficiency of nitrogen was nearly 1/5-1/10 of that of chlorine; and the efficiency of N₂-Cl₂ mixture gradually increased with the increase of the ratio of Cl₂:N₂. It is difficult to determine the ratio of Cl₂ for the highest efficiency: however, it should be generally concluded that the efficiency was comparatively high when the ratio of Cl₂ was within 20%. The efficiency of the mixture of 10% or 20% Cl₂ ratio was nearly 1/3.5 or 1/3, respectively, of that of chlorine.
(2) It was more effective when the gas mixture was used in combination with fluxes such as NaF or ZnCl₂; however, almost no effects of chlorine ratio were given on the results of efficiency. Therefore, satisfactory results were given by a harmless mixture of small content of chlorine. NaF seemed to be more effective than ZnCl₂.
(3) The reduction rate of Mg content in Al-Mg alloys increased in propaortion (being expressed in almost a straight line) to the ratio of chlorine.

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It is well known that cast structure of aluminum and its alloys is refined by the addition of rare earth metals (La, Ce, and mischmetal).
The studies reported in this paper are on the effects of rare earth metals on cast structure and recrystallized grain size and also on mechanical and heat resistance of 99.8% Al.
The following results were obtained.
(1) Cast structure was refined by the addition of La (0.01%), Ce (0.048%), or mischmetal (0.11%) to 99.8% Al.
(2) Hardness, tensile strength, and elongation were slightly improved by the addition of rare earth metal to 99.8% Al.
(3) Recrystallized grain size was refined in the highest degree by the addition of La 0.24% to Al.

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The studies reported in this paper are on general phenomena on the figure and out-of-roundness on the counter-sink formed by drilling into pre-drilled hole, then, the drilling conditions and materials for obtaining almost the circular counter-sink with small out-of-roundness were researched. It was proved that out-of-roundness of the counter-sink was not always smaller with the larger diameter of pre-drilled hole, but it greatly depended upon working material and drill dimension; in other wards, number of sides of polygonal figure increased with the larger diameter of pre-drilled hole, while out-of-roundness increased with the hole diameter and then gradually decreased after it attained to the maximum value for a certain diameter. When the diameter was not less than 70% of drill diameter, out-of-roundness was not more than 5% regardless of working materials, drill dimension, and feed. Out-of-roundness of the counter-sink in soft materials was larger than that in hard materials.

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In the 1st report⁽¹⁾, the authors made studies on the structures and various properties of Lo-Ex alloy for cast pistons. Continued from the 1st report, the relation between the structures and properties by several heat-treatment is studied in this paper.
The results are summarized as follows.
(1) Among physical properties, it was conspicuous that coefficient of thermal expansion of hyper-eutectic type was smaller than that of hypo-eutectic type.
(2) Lo-Ex of hyper-eutectic type generally showed better tensile properties than hypo-eutectic type at room temperature. These properties were particularly remarkable at 0.2% of proof stress. However, almost no difference between two types of alloy was seen in hardness.
As to the effects of heat-treatment method, T₆ had the best effects on the both alloys, while little differences were seen among others, T₄, T₅, and T₇.
(3) There was little difference between the both types of Lo-Ex in abrasion resistance at room temperature.
(4) Ultimate tensile strength of the both types of Lo-Ex at any temperatures above 250°C was almost equal in value.
(5) From the standpoint of structural types, creep resistance of Lo-Ex of hyper-eutectic type was higher than that of hypo-eutectic type at both of 200 and 300°C. As to the effects of heat-treatment method, the degree of improvement in creep resistance was arranged in ascending order of T₇, T₆, T₄, T₅, and F.
(6) Lo-Ex of hyper-eutectic type had excellent properties of degassing.
In general, Lo-Ex of hyper-eutectic type is considered to be excellent in various properties. However, the degree of superiority or inferiority of mechanical properties due to the differences of heat-treatment methods is not the same in each item of measurements. Accordingly, it is more desirable to adopt proper structural type of Lo-Ex and method of heat-treatment in consideration of the size of piston produced and other economic factors involved.

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In the previous report, (1) the authors pointed out that the structure of Lo-Ex was affected by the presence of Ca and P. Lo-Ex, containing not more than 0.005% of Ca, showed hyper-eutectic type, while, containing not less than 0.005% of Ca, showed hypo-eutectic type. However, Lo-Ex of hypo-eutectic type was converted into hyper-eutectic type by the addition of P.
The studies on the mechanism of the structural change of Lo-Ex is reported in this paper.
The results obtained are summarized as follows.
(1) In ternary system of Al-Si-Ca, binary eutectic point of Al-Si shifted toward high Si side by the presence of Ca, and eutectic line of Al-Si extremely approached to the axis of Al-Si by further quenching.
(2) The effects of P, a well known element to obtain fine Si eutectics, were inhibited by the presence of Ca. It was considered that the formation of Ca₃P₂ was preferred to that of AlP.
(3) The results of researches by means of microautoradiograph and electron microscope showed that Ca was contained in α-Al solid solution, but its content in Si crystals was very smaller. In the presence of Ca and P together, Ca₃ P₂ was preferentially formed and uniformly distributed. AlP was secondarily formed and made up a heteromorphic nucleus of primary Si crystal. P, having been added to Lo-Ex of hypo-eutectic type, formed Ca₃ P₂ and inhibited the effects of Ca, by which binary eutectic point of Al-Si shifted. As the results, Lo-Ex was converted from hypo-eutectic into hyper-eutectic type.

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The wear and frictional properties of typical aluminum alloys for casting such as lautal, Lo-Ex, Y-alloy, and hyper-eutectic Al-Si alloy were described in the previous reports, hitherto. Among these alloys, hyper-eutectic Al-Si alloy showed a high wear resistance. Accordingly, the details of wear properties of the last alloy are studied in this paper. The results obtained are summarized as follows.
(1) When the alloys of the same composition are combined together, Al-Si alloys of rather low silicon content readily cause seizure. Then, the addition of not less than 20% of silicon should be required for the anti-wear property of Al-Si alloy.
(2) In the combination of Al-Si alloys with carbon steel, Al-Si alloys containing not more than 15% silicon had a tendency to toward seizure in relatively high speed sliding friction. However, in the combination of alloys with cast iron, they showed a high seizure resistance.
(3) It was difficult to find out the effects of refining of pro-eutectic silicon particles on wear resistance of hyper-eutectric Al-Si alloys.
(4) Accordingly, the amount of pro-eutectic silicon was a more important factor as compared with its size for the wear resistance of hyper-eutectic Al-Si alloys.

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The effects of casting pressure on mechanical properties, especially machinability, of pressure die castings of copper silumin are discussed in this paper and the following results were obtained:
When casting pressure was higher, the microscopic structure was more compact and both of shearing strength and hardness were more increased; in addition, the resistant force for turning (especially, its principal component) and drilling became greater so that machinability was deteriorated with the increase of pressure However, it seemed that there was no effects of pressure on the roughness of surface.

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