The strength of Al-Zn-Mg alloys are expected to be the highest among the known aluminum alloys. The alloys which have no content of copper are considered to be a kind of excellent structural alloys for welding.
In this report, the ageing characteristics of Al-Zn-Mg alloys (Zn=3.5-5.0%, Mg=1.0-2.0%) at considerably low temperatures were studied by measuring changes in hardness and dissolving rate in 1N HCl aq. solution.
The results obtained were as follows.
1) The dissolving rate continuously increased in the early stage of ageing and reached the maximum, after which it began to decrease with the progress of ageing. Therefore, it can be deduced that cluster and G.P. zone were generated in the primary stage of ageing since the increase in dissolving rate would be due to the concentration cell comprising Zn and Mg atoms; and in the secondary stage, an intermediate phase precipitated after passing through the maximum.
2) No prompt change of hardness appeared immediately after quenching. In other words, incubation period appeared in hardness-ageing curve prior to the onset of hardening and the period was highly affected by the both contents of Zn and Mg as well as ageing temperature.
Relation between incubation period and ageing temperature is represented by curve C. The period was shorter with the increase of the content of forming Mg Zn₂ or the increase of Mg in excess of forming MgZn₂.

抄録全体を表示

For the purpose of determing proper helix angles of twist drill on drilling wrought aluminum, the drilling tests under constant forced pressure were made on 17S-T4, 24S-T4, 56S-H, and 74S-T4 with respect to drilling resistance, drilling time, chip treatment, etc. by using a twist drill, in which the helix angle was varied within the range of 17-45°.
Some differences in results were noted among drilling conditions or kinds of materials. However, in general, torque was small and drilling time (the time required for drilling the unit thickness) was long when the helix angle was small. On the other hand, torque was larger and drilling time was shorter when the angle was larger. The minimum in drilling time was apt to appear at 30-40° of the angle, in particular, in low cutting speed. The change of torque, which was in inverse relation to drilling time, was not so distinct. In the scope of these experiments, the degree of machinability was lowest in 17S-T4 and was ranged in ascending order as 24S-T4, 56S-H, and 74S-T4, regardless of the dimensions of drill.

抄録全体を表示

Interfacial transition (from smooth plane to cellular structure) of Al-Si alloys in unidirectional solidification was investigated. The transition occurred at
where C₀=1.6×10^-6G/R
C₀: Initial content of Si in molten aluminum
G: Temperature gradient in molten metal
R: Rate of solidification
It was assumed that isolated pits on the interface were the starting points of transition. It was observed that the change of the width of elongated cells was inversely proportional to the value of G^1/4×R^3/4 The shape of adhered layer on the decanted interface was often different from that of real interface.

抄録全体を表示

It was expected that mechanical properties and electric conductivity of age-hardenable aluminum alloys will be improved by warm working at the ageing temperature. In order to study the effects of warm working on the said aluminum alloys, aldrey was drawn to the extent of 95% of reduction ratio at room temperature and in the range of 80-160°C after it had been subjected to solution heat treatment. Subsequently, it was again heat treated at 100-160°C and the process of ageing was investigated.
The results obtained were as follows.
(1) The hardness of the wire was the highest, when it was drawn at 140°C, while its electric resistivity was lower with the elevation of drawing temperature.
(2) The differences of tensile strength and electric conductivity were examined among cold drawn wire, the wire heat treated after being cold drawn, and the wire warm drawn at 140°C. The tensile strength of the warm drawn wire was higher than that of the wire heat treated after cold drawing, when the wirer was drawn to the reduction ratio of above 70%; while the electric conductivity of the former was higher than that of the latter, when the wite was drawn to the reduction ratio of above 30%.

抄録全体を表示

The object of this work was to investigate the relation between fatigue strength and number of pin-holes of metal specimens (the latter depended upon the gas content of the molten metal). The specimens were prepared from molten Lo-Ex having various contents of gas, which had been determined by reduced pressure solidification test. The number of pin-holes was counted by improved color check test. In the fatigue test, the number of cycles before rupture under ±12kg/mm² of repeated tension and compression stress was counted with Vibrophore type machine.
The results obtained were summarized as follows.
(1) When the gas content in the molten alloy increased, the number of pin holes on the surface of the specimen increased and the fatigue strength remarkably decreased; whereas, the tensile strength was scarcely affected by the gas content.
(2) The fatigue strength was high when the specimen had only a few (not more than 3-4/cm²) pin-holes and the majority (more than 1/2) of such specimens represented endurance limit of over 10⁷ cycles.
(3) The fatigue strength remarkably decreased when the specimen had many (not less than about 4/cm²) pin-holes and very few of such specimens represented endurance limit of over 10⁷ cycles.
(4) When the endurance limit was not over 10⁷ cycles, the relation between the endurance limit and the number of pin-holes was approximately expressed by a logarithmic linear function.
(5) In the practical work of melting and casting, it was found that fluxes containing moisture reduced fatigue strength owing to the increase of gas content in the molten metal.

抄録全体を表示

In recent years, the demand for wrough alloys of Al-Zn-Mg system has rapidly developed and the usage of their return scrap or secondary ingot will be a matter of importance. The increase of Zn content in the die-casting aluminum alloys derived from these secondary ingots would be supposed. However, the effects of increased Zn content on the properties of the products have not yet been made clear. The present paper reports the effects of Zn, being present as impurity, in the content equivalent to ADC 10 (aluminum die-casting alloy) on mechanical properties, corrosion resistance, etc.
The results obtained were as follows:
(1) When Zn content was up to 1.48%, tensile strength slightly increased with the increase of Zn, but no effects were observed when the content was over the above limit. When the content was up to 2.88%, yield strength of 0.2% was almost no affected. Moreover, Zn content had little effects on hardness.
(2) Zn content had little effects on elongation, but impact value slightly decreased only when the content was in the range of 1.48-2.0% while it was little changed for over 2.0%.
(3) In salt water (3%) immersion test, weight loss slightly increased with the increase of Zn content. Anode potential (saturated calomel electrode) gave a higher absolute value when Zn content was higher; which proved that Zn content also had effects on corrosion resistance.

抄録全体を表示