All of JIS aluminum alloy castings for pistons contain nickel. However, studies were made of new alloys of low prices containing no nickel, but having the same properties as the conventional alloy castings. No nickel alloys such as temporarily called 8C and 8D, corresponding to JIS AC8A and AC8B, respectively, have been studied for practical use. On the other hand, high silicon cast aluminum alloys "hyper silumin" such as temporarily called 10A 10B and 10C having high heat and wear resistances have been developed for high speed or heavy duty pistons. In these studies, the rod specimens of the above developed alloys such as temporarily called 8C, 8D, 10A and 10C were prepared to conduct turning machinability tests and compared their machinabilities with those of existing JIS alloys for pistons. The results showed that 8C and 8D had slightly higher machinabilities than AC8A and AC8B, respectively. However, the degree of tool wear was not negligible for these alloys. In particular, 10A and especially, 10C gave remarkable tool wear, which will be a serious problem in discussing material properties.
In the previous paper, the yield stress in hot extrusion of pure aluminum was determined from the analysis of experimental results and an empirical formula was established to calculate the maximum extrusion pressure. This paper describes that the yield stresses of various aluminum alloys were obtained by the analysis of experimental results in a way similar to that of pure aluminum. In order to determine the yield stress in hot extrusion of pure aluminum, the factors to be taken into account were strain rate, work hardening, and temperature elevation; while, in case of aluminum alloys of especially hard ones, strain rate and work softening had to be considered. An empirical formula for obtaining the maximum extrusion pressure from the chemical compositions was established for various aluminum alloys. Although yield stresses were determined from the experiments by using a number of billets having various lengths, a new experimental method using a billet of only one definite length was proposed in order to minimize the number of tests.
This investigation was made of the dark spotted area on the integrally colored anodic oxidation coatings of an extruded 6063 alloy deposited from organic acid baths. This spotted area was likely to appear on a large sized extrusion. The hardness of that area was little changed by ageing and black smut was formed by etching it with sodium hydroxide solution.The same phenomenon also appeared in the laboratory on the alloy, which had been heat-treated to precipitate β'-phase. It was considered that the spotted area was attributed to an abnormal precipitate by local slow cooling of the extrusion. It was also considered that the area was derived from the co-existence of different stages of ageing in the precipitate. It was confirmed in the laboratory that the current density was considerably varied in different stage of ageing in integrally colored anodic oxidation coatings.
Aluminum is a soft material, which shows a very complicated deformation in cutting. This paper describes dry othogonal cutting of commercial pure aluminum at low speed for the study of its cutting mechanism. The distribution of residual stresses on the surface layer was measured by X-ray diffractiometry and the effects of cutting conditions (such as nose radius of tool edge, depth of cut, and cutting speed) on the residual stresses were discussed. The results obtained were summarized as follows: In low speed orthogonal cutting of aluminum, all the residual stresses near the surface layer appeared on the compression side. Though the nose radius of tool edge increased beyond a range of some value (60 μ in this paper), there were observed no effects of increase in nose radius on the residual stresses. Therefore, the substantial nose radius concerned with cutting was nearly constant (6070 μ in this paper) even if the built-up edge grew up and adhered to the tool nose for increasing nose radius. When the depth of cut increased, the residual stresses were penetrated more deeply and the stress values also increased. In the range of such a low cutting speed, there appeared little effects of cutting speed on the residual stress. However, the residual stresses slightly increased with the increase in cutting speed.
The relation between the ageing processes at low temperatures and compositions of two-phase (α+T) Al-Zn-Mg alloys were studied at 051°C mainly by electric resistivity measurements and also by hardness measurements and transmission electron microscopy. Ten sorts of alloys, having different total amounts of solutes and different Zn/Mg ratios were prepared for specimens. Such factors as quenching and ageing temperatures and quenching rate were different in each specimen. Principal results obtained were as follows: (1) The initial ageing rate increased with increasing total amount of solutes, and it also increased with increasing Zn/Mg ratio among the specimens of the same content of (Zn+Mg) at.%. On the other hand, the slow reaction rate was lower for the specimens of higher Zn/Mg ratio. The binding energy between a vacancy and a Mg atom was supposed to be less than as expected. (2) In each specimen, the quenching temperature had little effect on the initial ageing rate, but the slow reaction rate was lower with the rise of quenching temperature. (3) Air cooling from the quenching temperature resulted in only the mere decrease of the initial ageing rate in every specimen as compared with the normal quenching. However, the rate in the latter stage remarkably increased. It was confirmed that precipitates were formed during the air cooling in every specimen, and their quantity was larger in the specimens of higher Zn/Mg ratios and higher contents of (Zn+Mg). (4) The ageing behavior of these alloys would be explained as follows. Assuming that the interaction between two solutes is negligibly little, the diffusivity of Zn atoms is very greater than that of Mg atoms. Therefore, the migration of Zn atoms leading to the formation of clusters (rich in Zn) had effects on the process of initial ageing, particularly in the alloys rich in Zn. However, the migration of Mg had effects on the process of the latter ageing. It is out of question that the supersaturation of alloys had effects on the ageing process.
The relation between the ageing processes and various compositions of two-phase (α+T) Al-Zn-Mg alloys were studied mainly by specific heat measurements and also by electric resistivity measurements and transmission electron microscopy. The results obtained were as follows: (1) There were observed two sorts of endothermic change and one exothermic change on the specific heat-temperature curves (S-T curves) in all the specimens aged at low temperatures. However, the detailed shapes of curves considerably varied according to the compositions of specimens. The changes in the shapes of resistivity-temperature curves corresponded well with those in the shapes of S-T curves in each specimen. (2) The changes in S-T curves due to the compositions were mainly explained by the following facts. The amount of G. P. zones formed during pre-ageing was much larger, but the amount reversed during heating was much smaller in the specimens of higher zinc content; and the conversion of GP. zone→η' or η'→η was much easier in these specimens. (3) In particular, a complicated shape (with small endothermic changes) was observed in the exothermic part of S-T curves in zinc rich specimens. It was found that the above endothermic changes were owing to the dissolution of the previous phase into matrix at the end of a certain transformation in the process of continuous precipitation. The changes in S-T curves of the specimens aged at high temperatures were also discussed in detail. (4) The above results were in good agreement with those obtained by electron micrographs. In addition, interesting knowledge was acquired on the nucleation of T phase in η phase, on abnormalities of S-T curves in zinc rich specimens, etc.
The characteristics of crucibles made of graphite, mullite, alumina, and stainless steel (SUS 27) were examined for the purpose of retaining a molten aluminum sample in the extraction tube of gas measuring apparatus. The gas volume extracted by these crucibles or blank gas volume was measured, and hydrogen contents of aluminum samples were also measured from vacuum fusion extraction method by using these crucibles. The results showed that a crucible made of SUS 27 was more excellent in characteristics than those of other ones. Then, the following tests were conducted by using the SUS 27 crucible. (1) Reliability of measured values of hydrogen in aluminum obtained by vacuum fusion extraction method. (2) Distribution of hydrogen in the aluminum castings poured into the Ransley's chill mold. (3) Correspondence of the measured values with those by solid extraction method. The results obtained were as follows: (1) Standard deviation of the measured values of hydrogen in extruded aluminum rod was 0.003cc/100g. (2) Distribution of hydrogen in the castings poured into the Ransley's chill mold was not uniform. (3) Measured values by vacuum fusion extraction method corresponded well with those by vacuum solid extraction method.
Studies were made on corrosion resistance of high aluminum zinc base alloys by electro-chemical method, particularly on the effects of aluminum content, copper addition, addition of small amounts of other elements, and heat treatment. The results obtained by (1) RGY tests and (2) corrosion potential measuring method were summarized as follows: (1) RGY tests It was shown among Zn-Al binary alloys that the current for bath voltage of Zn-22%Al alloy was higher than those of other high aluminum content alloys. In the alloys containing aluminum of more than 22%, the current for bath voltage decreased with the increase of aluminum content. The corrosion resistance of Zn-22%Al alloy was considerably improved by addition of copper of 15%; and the optimum content of copper would be 1%. The above corrosion resistance was reduced to minimum when the alloy was heated at 350°C for 24hrs., and then, water-cooled. The corrosion resistance of Zn-22%-Cu1% alloy was improved by addition of a small amount of Ti, but was deteriorated by addition of a small amount of Ni. (2) Corrosion potential measuring method Among Zn-Al binary alloys, the corrosion potential of Zn-22%Al alloy became less noble after it was dipped in the solution for 1hr. The corrosion potential was nobler with the increase of aluminum content. The corrosion potential was slightly nobler by addition of copper to Zn-22%Al alloy. However, the improvement in corrosion resistance of Zn-22%Al-1%Cu alloy could not be attained by addition of small amounts of other elements such as Mn, Ti, Ni, Mg, Zr, and V.