A slot bar and a ring in a cage type cast rotor of an induction motor are usually die-cast with pure aluminum. However, high electrical resistance alloys with electrical conductivity below 25% IACS and moderate mechanical properties such as tensile strength of 15kg/mm² and elongation of 2% are required for cast rotor materials of a high starting torque motor used for hoist and machine tools. In this report, effects of Cr, Mn, Ti, Fe and Zr on electrical and mechanical properties of Al-8.5%Si-3%Cu were studied with a statistical analysis. From this study, an Al-8.5%Si-3.0%Cu-1.0%Cr-0.5%Mn-0.3%Ti alloy was obtained as a base alloy of high electrical resistance. The alloy had electrical conductivity of 22-24% IACS, tensile strength of 18-20kg/mm² and elongation of 2-3% and showed good castability. A motor with a rotor, die-cast with the alloy, showed satisfactory motor characteristics as a high starting torque motor.

View full abstract

The phase equilibria in the aluminum-tantalum system were studied by metallography, X-ray analyses and melting point measurement techniques. There are two intermediate phases in this binary system and they were identified as TaAl₃ and Ta₂Al. The TaAl₃ phase is tetragonal structure of TiAl₃ type and the lattice parameters are a = 5.43₂Å, c = 8.580Å and c/a = 1.579. The TaAl₃ phase has an extensive range of solubility at elevated temperatures, ranging from 22at.%Ta to 32at.%Ta. The Ta₂Al phase is tetragonal structure of β-U type and the lattice parameters are a = 9.971Å, c = 5.127Å and c/a = 0.514.
The TaAl₃ phase forms congruently from a melt at 1550° ±50°C and the Ta₂Al phase forms peritectically at 2000° ±50°C. An eutectic reaction occurs at about 42at.%Ta and 1500° ±50°C between TaAl₃ and Ta₂Al. In the tantalum rich region of this system, a peritectic reaction occurs at 2000° ±50°C where liquid reacts with a tantalum solid solution to form Ta₂Al. The aluminum solid solution forms peritectically at 668°C between liquid and TaAl₃. The tantalurm solid solution crystallized out as a primary phase and the maximum solubility of aluminum in the tantalum solid solution is about 12at%Al at the peritectic temperature of 2000° ±50°C and abruptly decreases with decreasing temperatures.

View full abstract

Temperature dependence of 0.2% yield stresses and strain rate sensitivities of precipitation hardening Al-1wt.%Zr alloys, produced by rapid solidification, were studied over the range from 77°K to 500°K and activation parameters for plastic deformation of the alloys were determined as a function of temperature. The results obtaines are as follows:
(1) It was shown that below -400°K, the deformation mechanism in the as-cast (supersaturated) and the precipitation hardened alloys was the same as that in pure aluminum.
(2) Above -400°K, the activation energies in the as-cast and the precipitation hardened alloys became greater than that for the self diffusion in aluminum. The activation volumes in the precipitation hardened alloys, on the other hand, remained constant, -100b³, over the testing temperatures. However, the as-cast alloys exhibited an abrupt increase of the activation volume when the temperature exceeded 200°K.
(3) From the activation energies and volumes of the precipitation hardened alloys above -400°K, it was considered that the high temperature deformation mechanism in the precipitation hardened specimens was similar to that in a dispersion hardened alloy.

View full abstract

The present authors has previously reported that the retardation of aging due to Sn and Cd in Al-Cu-Sn and Al-Cu-Cd alloys was explained by the significant decrease of the Cu solubility in the α-phase by the small addition of Sn and Cd rather than by the vacancy-trapping mechanism. The purpose of this report is to reexamine the above conclusion from a point of view that the quench-clustering might affect properties of as-quenched specimens and aging behavior following quenching. Correction of aging curves was done by means of a usual extrapolation method accompanied by reversion experiments. The results obtained are as follows:
(1) Effects of quench-clustering on the properties were, in the present case, considered not to exist The phase diagram of the aluminum corner of the Al-Cu-Sn (Cd) ternary alloy, previously established, was further confirmed to be correct. The systematic changes in the experimental againg curves, produced by the changes of Sn (Cd) contents remained unchanged even when the aging curves were corrected. Thus, the previous conclusion needed no modification at all.
(2) Further, it was found that the experimental results reported by many research groups in the usual reversion treatment of the Al-Cu systems were not reliable. This was based on the transmission electron microscopic observation that the usual reversion treatment resulted in the θ' precipitation, which was more remarkable in the ternary alloys.

View full abstract

Aging phenomena of Al-Zn-Mg-(Cu) alloys with a small addition of Cr were investigated by means of hardness and electrical resistivity measurements, EPMA analyses and transmission electron microscopy. Various specimens based on the (α + T) type Al-Zn-Mg-(Cu) alloys were solution-treated at 470-580°C for 4hrs, quenched into iced water and aged at various aging temperatures, T_A. The results obtained are as follows:
(1) In the Al-Zn-Mg alloy, the initial aging rate decreased when T_A was below about 125°C, as Cr contents increased and solution-temperatures were lowered. Increases of Cr contents and high temperature aging above 150°C suppressed the age-hardenability remarkably. EPMA analyses showed that the solute contents of Zn and Mg in the E phase were much higher than those in the matrix. Thus, the Zn and Mg contents in the matrix inevitably decreased as the amount of Cr addition increased and solution-temperatures were lowered. This fact was considered to explain the aging suppression at low T_A in the Cr containing alloys. Further, an electron microscopic examination revealed that the preferential precipitation of the T phase took place on the E phse at high T_A. This suggests that the solute contents in the matrix were further decreased by the T phase precipitation. It was considered that the extremely low age hardenability of the Cr bearing alloys at high T_A was caused by this fact together with the simple decreasing effect of the solute content by Cr additions.
(2) In the Al-Zn-Mg-Cu alloy, the suppression of the initial aging rate at low T_A and the low age hardenability at high T_A were also introduced by a small addition of Cr. These were considered to be due to the same effect of Cr as in the ternary alloy.

View full abstract