The mechanism of growth of G. P. zones in Al-20%Ag, Al-5%Ag, and Al-5%Ag-0.04%Sn alloys was examined by electric resistivity measurements and tensile tests.
The existence of two kinds of G. P. zones, ε and η, was confirmed in these alloys, and their ageing characteristics were satisfactorily explained in terms of the metastable miscibility gap given by Baur and Gerold. However, it was shown that the ε-η transition temperature in low silver concentration was much higher than the value expected from the metastable miscibility gap.
It was found that ε was made coarser according to the Ostwald ripening mechanism in later stages of ageing. The activation energy of growth of ε was determined to be 21.7kcal/mol.
Tin retarded the clustering during quenching and in the earliest stages of ageing, but accelerated the G. P. zone development in the next stages. After prolonged ageing, the effects of tin on the growth of ε were very little.
Effects of the quenched-in vacancies in later stages of ageing were also discussed.

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The mechanism of reversion in Al-20%Ag alloy aged at 70° or 130°C for different periods was investigated by measurements of electric resistivity and proof stress.
The resistivity of aged alloys was increased to the maximum, and then, decreased. While, the proof stress was only linearly decreased. The degree of reversion was satisfactorily explained in terms of the metastable miscibility gap given by Baur and Gerold.
The diffusion processes during the reversion was analyzed in reference to the metastable miscibility gap. It was shown that the reversion was due to the transition from η into ε zone, not due to the solution of G. P. zones. The activation energy of the diffusion of Ag during the reversion was determined to be 29.0kcal/mol by considering changes in the matrix concentration and the zone size depending upon the reversion temperature according to the metastable miscibility gap. The value was in remarkable agreement with the activation energy of diffusion of Ag in Al and Al-Ag alloy, or 29.0 and 28.9kcal/mol, respectively. Therefore, it was concluded that the rate controlling step in the reversion of Al-20%Ag alloy was the diffusion of Ag in Al-Ag solid solution.

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Failures due to thermal fatigue often occur in aluminum alloy pistons and cylinder heads of engines, especially in those of Diesel-engines owing to their high operating temperatures.
This paper reports a method for investigating the resistance of aluminum alloys to thermal fatigue and the phenomena in thermal fatigue tests of Al-Si base alloy castings.
The results obtained were summarized as follows:
(1) It was found that a high rate thermal cycling could be achieved with a thermal fatigue testing apparatus of high frequency induction heating type (not the Coffin type.)
(2) The number of cycles to failure was decreased with the increase in temperature amplitude, thermal stress amplitude, and plastic strain amplitude.
(3) Specimens were tested at an average temperature of 300°C; they were radially expanded in the section heated to the maximum temperature and necking appeared in the both ends of the expanded section. The deformation of specimens was related with the distribution and variation of hardness in the specimens. The hardness was decreased in the section heated to above 300°C; and was minium in the necked parts, wehre the fracture took place.

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