Continued from the previous paper (1st report) on "Ductile type striation, " this paper discusses on the detail of brittle type striation by means of electron fractography.
Brittle striations have been observed only in age-hardened aluminum alloys. They were characterized by relatively flat facets periodically marked by deep grooves. Numerous river line markings separating these facets ran normal to the striation. In the brittle crack growth, the crack front was bent in semi-circular form, but the ductile growth was relatively straight fronte d.
In Al-1.5% Mg₂Si alloy, the length of a side of the small facet compristing the striations and river line markings was an order of about 0.10.2μ, which was nearly the same magnitude as the length of acicular particles or interparticle spacings observed by electron microscopy.
The brittle type striations showed different aspects of microfeatures under different conditions. As the results of analysis, the main features of the brittle type striations were as follows.
(1) Even if the appearance of the striations was not distinct, the characteristic feature was observable relating to the distribution of precipitates.
(2) The striations were bent in the neighborhord of large steps and it was suggested that the advence of crack front was arrested in the neighborhood of the steps.
(3) There are many types of intermediate fracture topography with respect to the macroscopic direction of fatigue crack propagation and the orientation of individual grains (namely, microscopic direction of fatigue crack propagation).

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Investigations were made on the effects of the addition of Cr, Ti, and Be on macrostructure and mechanical properties of Al-5% Si-(0.50.8%) Mg-(0.72.0%) Zn alloys and the following results were obtained.
(1) The change in macrostructure of Al-5% Si-0.5% Mg-1% Zn alloy depended upon Be content, and the grain size of the alloy was refined by the addition of 0.1% of Be.
(2) Al-5% Si-(0.50.8%) Mg-(0.72.0%) Zn alloys, which had contained 0.1% of Be and been degassed by ZnCl₂, had refined macrostructure. After cast in sand mold and T6 treated, the tensile strength of these alloys was increased to 42 kg/mm² and their elengation reached over 2%. It was found that the effect of improving tensile strength by the addition of Be was greater in the test pieces of sand mold than those of metallic mold. When sodium was contained in these alloys, they were likely to have coarser macrostructure and lower tensile strength.
(3) When each of Be, Cr, and Ti was added to Al-5% Si-(0.50.8%) Mg-(0.72.0%) Zn alloys, the effect of additional elements on tensile strength and proof stress of test pieces of metallic mold was almost negligible. However, elongation was slightly improved by the addition of Be.

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Several kinds of surface-treated aluminum alloys were dipped in sea water for one year and their corrosion effects were observed.
The results obtained were as follows.
(1) Among surface treatments such as as pre-treated MBV process, anodizing in sulfuric acid, painting of organic poisons, specimens by the latter two treatments were never corroded because of short dipping times.
2) All the specimens treated by MBV process were corroded after dipping for one year and their anticorrosion effect was not very hopeful.
(3) The maximum depth of pits formed on the specimens of non-surface treated or MBV treated increased with the increase of dipping time. The depth was large for pure aluminum (such as 1050 and 1100) and 6063 alloy, but it was relatively small for 3003 and 5052 alloys. In alclad 3003 alloy, the core part of 3003 alloy was protected, though the clad part of 7072 alloy was corroded.
(4) The relationship between corroded parts and location of barnacles was observed and it was known that many deep pits were formed close to their shells and that several parts just underneath the shells seemed to be dissolved. It was supposed that these results were due to crevice corrosion attack or corrosion effects of secretions of barnacles. Accordingly, the sticking of barnacles was not desirable for aluminum.

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Effects of friction and lubrication on the deformation resistance are considered one of the most important problems in compression tests. This paper describes the basic factors in friction behavior of lubricants relating to the aspect ratio (diameter/height) of specimens.
(1) When colloidal graphite oil was used as a lubricant, the following results were obtained on the mechanism of boundary lubrication. A close relationship was found between microstructure of worked surface and coefficient of friction. The rate of effects of lubricant depends on the surface roughness of the specimens. For example, when the side of specimens was roughened to about 8μ (Hmax by polishing with carborandum paper, it had superior lubrication to that of mirror-like finished surface.
(2) When various sorts of lubricants such as liquid, semisolid, and solid were used as lubricants, frictional force and coefficient of friction were fairly varied according to their viscosities. For example, solid lubricants had higher holding power of lubricant films than others, and they were known to be suitable for high plastic workability.
(3) The aspect ratio and friction coefficient of specimens were thoroughly discussed with respect to Siebel's theoretical equation (P/Y=1+μd/3h) in order to develop a new field of compression tests.

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Studies were made on eutectic-melting and micro-fissuring in welds of Al-Zn-Mg alloys.
In this paper, there are discussed the effects of metallurgical factors on micro-fissuring in welds and its mechanism.
The results obtained were summarized as follows.
1) Micro-fissures were often observed in multi-pass welds of Al-Zn-Mg alloys as well as Al-Mg, Al-Mg-Si, Al-Cu and Al-Zn-Mg-Cu alloys.
2) The formation of micro-fissures depended upon inter-layer temperatures, welding conditions, number of passes, thickness of plate, compositions of base and filler metals, restraint and other factors.
3) The more micro-fissures were observed in weld with the increase of heat-input to weld.
4) Micro-fissuring due to eutectic-melting mainly depended upon boundary segregation of eutectic composition with low melting point. However, the peculiar characteristics of grain boundary itself were not negligible.
5) Sequence of formation of micro-fissures in aluminum alloys and its mechanism could be discussed in connection with normal weld cracks.

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Galvanic corrosion of aluminum alloy castings, composed of 99.8% Al, Al-5% Cu, Al-4% Si-4% Cu, Al-11% Si, Al-7% Si-6% Cu, and Al-5% Mg, was investigated in contact with 18-8 stainless steel, mild steel, and copper in 5% NaCl aqueous solution at 35°C and at boiling point under ordinary atmospheric pressure. corrosion behaviors of these alloys at boiling point were quite different from those at 35°C. The increasing order of corrosion rate of the aluminum alloys at 35°C was arranged as follows.
Al-5% Mg=99.8Al<-11% Si<Al-7% Si-6% Cu
However, the above order was observed inversely at boiling point.
Al-5% Mg was most strongly attacked among these alloys when it was coupled with the stainless steel at boiling point. High corrosion rate of this alloy was attributed to Mg(OH)₂ formed in the solution, because of its basicity. The corrosion rate of aluminum would be high under this condition. Al-7% Si-6% Cu was least corroded; in particular, very little galvanic effect was observed when it was coupled with mild steel.
The gravimetric loss of weight on galvanic corrosion of pure aluminum was about three times as large as that calculated from the current flowing through the galvanic couple.
Maximum galvanic current was observed at about 75°C in the couple of pure Al-mild steel or pure Al-copper. However, extraordinary large galvanic current was observed in the couple of pure Al-stainless steel.

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