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Hot deformation studies using torsion testing were conducted on high purity Al and Al-4 at. pct Mg alloy systems in the strain rate range of 0.1 to 1.0 s−1 and temperatures up to 810 K (1000‡F). At all test temperatures, the flow stress of the Al-Mg alloy was higher than that of pure AL The strengthening in hot working (above 522 K (480°F)) is suggested to be due to a higher equilibrium subgrain forest dislocation density. Special quenching procedures were required to show this correlation. Conventional quenching fails to show this because structural details are lost when quenching from high temperatures.

Stress corrosion cracking (SCC) has been studied in an Al-Li alloy with variables of orientation of specimen, heat treatment, and applied potentials. The distribution of the electrochemical potential resulting from precipitate clusters was measured, and the hydrogen content on the specimen surface was detected. The results showed that the SCC susceptibility under the peak- aged (PA) condition was higher than that under the natural (NA) and overaged (OA) conditions. The transverse (TL) specimen was more susceptible to SCC propagation than the longitudinal (LT) specimen. The SCC susceptibility and the hydrogen content on the specimen surface were dependent on the applied potentials. The hydrogen content increased when the applied potential changed to positive or negative directions. There was a critical hydrogen content, below which local anodic dissolution (LAD) plays an important role, above which hydrogen embrittlement (HE) plays an important role.

The microstructure, texture, and whisker orientations in 6061 Al-20 wt pct SiC whisker composites have been examined using transmission electron microscopy and X-ray diffraction. Tension creep tests of the composite material have also been conducted in the temperature range 505 to 644 K (450 to 700 F). The steady state creep rate of the composite depends strongly on the temperature and applied stress. The stress exponent for the steady state creep rate of the composite is approximately 20.5 and remains essentially constant within the range of test temperatures. The activation energy is calculated to be 390 kJ/mol, nearly three times as high as the activation energy for self-diffusion of aluminum. No threshold stress was observed. Fracture surface examination using scanning electron microscopy shows that the composite fails by coalescence of voids in the aluminum matrix which originate at the aluminum-SiC interface. It is demonstrated that SiC paniculate composites are less creep resistant than SiC whisker composites.

This paper describes new rate equations which fit exactly the experimental data of carbon precipitation from supersaturated α iron. The experimental data reported by Abe and Suzuki, electrical resistivity, thermoelectric power, and Vickers hardness, are used. A low carbon steel is quenched from 700°C and aged isothermally in the range from 35 °C to 300°C. Aging curves are separated into two curves corresponding to characteristic precipitates, and superposition of the two curves elucidates the reason why two-stage aging curves often appear. The separation of aging curves clarifies the temperature dependence of each precipitation, and activation energies of 0.57, 1.21, 0.80, and 1.45 eV are obtained for cluster, e carbide formed below 75 °C, ε carbide above 100°C, and cementite, respectively.

The role of interaction between slip dislocations and [110] tilt boundaries in crack nucleation has been analyzed for the face-centered cubic (fcc) and L12 structures. Dislocation absorption into the boundaries is orientation-dependent according to the elastic anisotropy. Whenthe transfer of slip across the boundary is impeded, cleavage fracture is predicted on the (1¯11) plane. Intergranular fracture can be initiated when a symmetric double pileup of primary slip dislocations from both sides of the boundary occurs simultaneously. The available experimental data on slip/grain boundary (GB) interaction and intergranular fracture are in good agreement with the present predictions.