This paper reports the study which was carried out on the fatigue properties of welded butt-joints made of 5356 or Al-Zn-Mg alloy filler metals in TIG welding of ZG43 or ZQ50 Al-Zn-Mg alloys.
The fatigue tests were conducted with Schenck's plane-vibrating fatigue tester and the values of fatigue strengths were determined by 10⁷ cycles.
The fatigue strengths of butt-joints without and with reinforcement of weld are shown in Table 6. The effects of difference in the kinds of employed filler-metals or conditions of heat treatment before the welding of base-metals had no remarkable effects on the fatigue strengths of welded butt joints. The tempering treatment after welding slightly depressed the fatigue strengths from those values of as welded.
In order to explain the facts mentioned above, the fatigue tests of ZG43 bar specimens, notched and unnotched, were conducted with a rotary-bending fatigue tester. The notch sensitivity increased with the rise in tempering temperature up to 140°C as shown in Fig. 12.
With respect to the fatigue properties of butt joints in Al-Zn-Mg alloys, the authors concluded as follows:
(1) T4 treatment of base-metal was superior to T6 treatment.
(2) Tempering treatment after welding was undesirable.
(3) The same properties were obtained by the filler metals of 5336 as by those of Al-Zn-Mg Alloys.

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This study was carried out on the notch effect up to 5.8 of theoretical stress concentration in fatigue strengths of 15 sorts of extruded Al-Zn-Mg alloys.
The fatigue properties were examined with Ono's type rotating-beam fatigue tester, and the fatigue strengths were determined in 10⁷ cycles.
The fatigue strengths decreased with the increase of sharpness of notch up to 3.0 of theoretical stress concentration, but they approached to nearly a constant value for further increase of the sharpness. When the notch of specimens was not deep, the alloys having high tensile strength showed higher fatigue strength as compared with these having low tensile strength. Notch fatigue factor of the specimens was smaller than the theoretical stress concentration.
The effect of heat treatment on notch sensitivity was the greatest in the values obtained by as-extruded materials (F). The value of the sensitivity in T4-treatment was smaller than that of T6-treatment.

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The differential volume change method was devised by the authors. As well known, as-quenched alloys have many vacancies which affect ageing rate. Many researches have been published to clarify the effects of these vacancies, but most of the researches were conducted by means of indirect measuring methods; for example, by an electrical resistance method, etc. Moreover, analyses were not accomplished by small angle X-ray reflection, because atomic number 13 of Al is situated at between numbers of Mg and Si, which are 12 and 14, respectively. In this study, the authors newly devised a direct method capable of measuring volume change due to the variation in number of vacancies.
The volume change was measured by the variation in buoyancy of aluminum alloy specimen immersed in special corrosion-resisting solution. For this purpose, the micro-balance of 1/100mg in accuracy (see Fig. 1) was employed. The balance was set in the room at 20°C for prevening the effects of air convection on either of two pans.
The special corrosion-resisting solution (1ppm of Na₂SiO₃ in pure water) was employed. Although the rate of corrosion was extremely low, aluminum specimens were generally corroded in pure water or city water. The corrosion was ascertained by gas bubbles adhered to the surface of specimen after immersed for 1/2 or 1hr. However, they were not the original adhesion of air before immersion. Against all endeavors to inhibit the corrosion of quenched specimen mentioned above, a very trace of corrosion would not possibly be avoided even under the formation of barrier layer. As a countermeasure, the differential measurement was devised. A quenched piece and an annealed one, having same compositions and same dimension (65×45×3mm), were prepared.
The former piece was for use for ageing test and the latter was for balancing weight.
The change of weight corresponding to the variation in buoyancy due to volume change of the quenched specimen under the above conditions was continuouly measured for 500hr. or more. (A wire of the same composition as that of the quenched specimen was employed for hanging both the specimen and the balancing weight in the solution. The vessel, holding the immersing solution, was placed in a larger vessel of holding water for preventing the temperature change of the solution).
Test results: The differential volume change of Al-1.4% Mg₂Si due to ageing at 20°C is shown in Fig. 3. (For comparison, Fig. 2 and 4 show disappearing of quenched-in vacancies of 99.999% pure aluminum after being quenched from 500°C and of Al-1.4% Mg₂Si after artificially aged at 150°C for 20hr. However, no expansions are observed at initial period of ageing).
In Fig. 6, which shows the analysis of ageing conditions of Al-1.4%Mg₂Si at 20°C, ABCD represents the observed differential volume change due to ageing at 20°C immediately after quenched, and OE represents the supposed vacancy sink line drawn in parallel to the region of BC (that is, the observed curve corresponding to disappearing of vacancies).
OFG, which is obtained by the superposition of ABCD and OE, may show the volume change solely due to clustering of the quenched alloy. OFG is nearly parallel to OHI which shows the observed hardness change due to the ageing.
Proceeding of ageing can be expressed by curves of OFG and OHI, which are in parallel each other, and by volume change (represented by OFG) solely due to clustering.
It is most noticeable that the rapid rate of clustering was in advance of the rate of vacancy disappearing at the initial period of clustering.
In other words, clustering rate is slightly greater than the rate of vacancy disappearing. However, the both rates were equal before the lapse of a long period and the vacancy disappearing at 20°C continues for a long time.
In contrast to the ageing at 20°C, volume expansion due to ageing at

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The electric discharge grinding of titanium was researched by R-C circuit on machining conditions, state of machined surface, change in the structure around the machined surface, etc.
The results showed that titanium could easily be rough-machined by electric discharge grinding, but the machining speed was greatly affected by the conditions such as source voltage, current for machining, capacity of condenser, circumferential speed of electrode disc, etc. For example, the machining efficiency increased with the rise of source voltage; however, the highest efficiency was found at some degree of current, condenser capacity, circumferential speed of the disc, etc. The efficiency decreased at either below or above that degree.
The machined surface was satin finished, being assembled of many discharge craters, and its degree of roughness was ordinary higher for higher machining speed. Some ground materials were slightly hardened by electric discharge machining; in particular, the hardness was distinguished around the machined surface for low disk speed.

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The effects of alloying elements, their concentrations, and conditions of solidification on the formation of feathery crystals were investigated on 10 kinds of binary aluminum alloys uni-directionally solidified in insulating (Isolite) mold. The possibility of formation of feathery crystals was explained with respect to the rate of solidification (R) and temperature gradient in liquid phase in front of the solid-liquid interface (G_l).
The following results were obtained.
(1) The feathery crystals were formed in the following 6 kinds of binary alloys:
Al-Fe (0.72-2.05%), Al-Sn (3.94-9.76%), Al-Cu (10.47-14.99%), Al-Mg (5.06-10.10%), Al-Ni (1.02-3.75%), and Al-Ti (0.08-0.13%).
On the contrary, the crystals were not found in the following 4 kinds of alloys.
Al-Si (1.0-10.0%), Al-Mn (0.5-4.0%), Al-Cr (1.0-4.0%), and Al-Zn (1.0-10.0%).
(2) The feathery crystals in the above 6 kinds of alloys were not formed in the range of low concentration, but were more easily formed in higher concentration.
(3) The feathery crystals in 5 kinds of alloys were more easily formed with the increase in solidification rate (R), temperature gradient (G_l), and the ratio of G_l/R1/2.
(4) As the results of (2) and (3) described above, it was found that G_l/R1/2 should be increased with the decrease in concentration of alloying elements for the formation of feathery crystals in the Al-Fe alloys.
Furthermore, the mechanism for the formation of feathery crystals was proposed as follows; the formation of twin crystals would be favorable to eliminate the instability due to constitutional supercooling. It was also assumed that the effects of alloying elements on the formation of feathery crystals would depend on distribution and diffusion coefficients of elements in molten state.

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