Although aluminum is a metal of high corrosion resistance, it sometimes suffers local corrosion in exposure test or water immersion test.
With the object of proving the corrosion, tests were conducted in aerated and deaerated pure water at 35°C. In aerated pure water, a milk-white ring was produced around the metallic compound and a pit was formed in the ring.
The results obtained were summarized as follows.
(1) In annealed aluminum of high purity, a kind of zone (like denuded zone) was formed along the grain boundary (perhaps it may be due to a small amount of impurities contained) and intergranular corrosion occurred in these zones in aerated or deaerated pure water at 35°C.
(2) When 1100 aluminum was immersed in aerated pure water at 35°C, a milk-white ring was produced around a compound α (Fe-Si) owing to the potential difference between the compound and aluminum matrix; and a pit was formed in the ring. Even after the formation of the pit, the depth of the pit more increased owing to the action of concentrated cell in aerated water. Aluminum was far more rapidly corroded in deaerated pure water at 35°C as compared with in aerated pure water.
(3) When 3003 aluminum was immersed in aerated pure water at 35°C, a milk-white ring was produced around a compound (Fe-Si) and a pit was formed in the ring. However, no pit was formed around a compound (MnAl₆). On the other hand, in deaerated pure water, a pit was generally formed around the both compounds.
(4) When X8001 aluminum was immersed in aerated or deaerated pure water at 35°C, only a very small pit was formed.
(5) The oxide film formed on aluminum of 99.99% purity, which had been corroded in aerated or deaerated water at 35°C, was bayerite.

View full abstract

The stressed state in cutting is very complicated. For instance, it can be regarded to correspond to the rupture under hydrostatic pressure. The correlation between the rupture characteristics in cutting and the rupture under simple stressed state is still unknown.
In this paper, the rupture under combined stress of torsion and compression was examined on several sorts of wrought aluminum alloys in order to obtain the corresponding rupture characteristics in cutting.
When specimens were twisted under compressive stress, no great change was observed in shearing stress toward rupture, but shearing strain toward rupture remarkably increased resulting in the delay of rupture. It was proved that rupture characteristics under compressive stress was different from the characteristics under no compressive stress. For the purpose of reproducing the state of stress-strain in cutting, the rupture characteristics under combined stress should be evaluated by compression-torsion test, although there may be a few problems still unsolved such as the change in diameter, etc. under compressive load.

View full abstract

Aluminum (such as 2S)plate is very inferior to aluminum alloy plates in drilling machinability. That is, when it is drilled by using conventional drills, the dimension of the hole obtained was not good in accuracy and many problems are brought out in its drilling.
This paper reports drilling machinability of 2S plate by using a twist drill of conventional types with respect to the magnitude of oversize of the hole, heap at the hole inlet, burr at the hole outlet, drilling resistance, shape of chips, etc.; and the experiments were made for the purpose of determining proper drilling conditions for 2S. In addition, a fishtail point drill, having a specially ground shape of tip, was also examined for drilling, because it is told to be effective for drilling 2S.
Drilling tests were conducted under constant feeding speed and constant pressed force by using a commercial twist drill of 10mmφ. The results obtained were as follows:
(1) In drilling by using a non-thinned drill of ordinary type, the magnitude of oversize of the hole inversely increased with the decrease of the heap or burr.
(2) There were no remarkable effects of thinning on magnitude of oversize, heap and burr.
(3) In drilling by using a fishtail point drill, the magnitude of oversize of the hole often increased at the hole outlet, but the drilling conditions were much better, although drilling resistance was higher than ordinary drills.
Accordingly, the above results would be explained by ship of the drill, constrained motion of drill edge, precessional motion of the drill, shape of drill margin, etc.

View full abstract

An attempt was made in statistical method to find out the correlations between various properties of a series of aluminum alloys for casting pistons and alloying constituents or casting conditions. The above alloys contained Si-12-21%, Cu-1-5%, Mg0.5N-1.5%, Ni-0-1%, and P-0.16-0.24% (additional).
Ultimate tensile strength at room temperature increased with the increase in Cu content, but decreased with the increase in Si content. The maximum strength was achieved by the addition of 0.5% of Mg. The contents of Si and Cu had no effects on the strength at elevated temperatures. Increase in Si content (in particular, higher than 18%) was effective for elongation and creep resistance at elevated temperatures.
Hardness at room temperature increased with the increase in Si or Cu content. Si content had a certain effect on fluidity. When P was not contained in binary Al-Si alloys or in quinary high-Si alloys, the fluidity was maximum at 18% of Si. While, P was contained in the above alloys, it was maximum at 24% of Si. Increase in Si content induced the reduction of sinking and the development of macro-shrinkage. Increase in Cu and Mg contents slightly accelerated micro-shrinkage. Primary crystals of Si were coarser when Si content was higher.
The introduction of red phosphorus (up to 0.16% of P) would be more effective for refining Si crystals, and the effects were still unchanged for more amount of P.
Both specific density and thermal expansion decreased with the increase in Si content. Consequently, the most successful properties were achieved at the composition of Si-18%, Cu-5%, Mg-0.5%, Ni-0%, and P-0.16% (additional).

View full abstract

The feathery crystals of Al-Mg (7.08%) and Al-Fe (0.68 & 1.5%) alloys were formed during upward unidirectional solidification in insulating (Isolite) mold with chill plate at the bottom. The crystals formed were studied by various methods such as macroscopic and microscopic observations, etching pit method for estimating crystal orientation, microscopic observations and surface inspection testings on decanted interface. The following conclusions were drawn.
(1) The feathery grains consisted of thin lamination layer of crystals having twin plane of (111), and its growth direction was presumed to be <112>
(2) It seemed that as a single feathery crystal began to grow, numerous lamellae of feathery crystals were successively formed in almost parallel direction, which showed laminated structure.
(3) As the results of microscopic observations and surface inspection testings on structure of decanted solidliquid interfaces, it was concluded that feathery grains grew prior to dendrites.
(4) An excess of iron segregation was recognized at a position, which was assumed to be an original source of feathery crystals in Al-Fe (0.68 & 1.5%) alloys. The segregation would be due to the local accumulation of rejected solute in Al-1.5%Fe alloy, while Al-0.68% Fe alloy caused banded segregation.
(5) By the observations of several cross-sections, 3-dimensional growth behavior of feathery crystals was explained.

View full abstract