An extrusion process for finely grained, recycled hot extrusion material fabricated by hot pressing chips obtained in machining of AZ91D, has been investigated for achieving its higher strength and higher strain-rate superplasticity. Fine dispersion of β-phase (Mg₁₇Al₁₂) particles in the matrix of the pressed billet, was obtained through solution heat treatment at 723 K followed by aging at 523 K. Further, by cooling the gate of the extrusion die with nitrogen gas during the hot extrusion, the temperature rise of the extruded billet was suppressed, resulting in fine grain sizes. The combined method of the solution heat treatment and the nitrogen-gas cooling during the extrusion, made it possible to refine average grain size of the extruded material down to less than about 3.5 μm, improving its room temperature strength and superplastic property. The grain refinement was especially effective to improve 0.2% proof stress of AZ91D extrusion alloy. The AZ91D alloy extruded at a temperature of 553 K, showed a superplastic elongation of about 250% at a tensile test temperature of 548 K and a high strain rate of 1×10⁻² s⁻¹. The strain rate sensitivity index m of the observed superplasticity was about 0.56. During the superplastic deformation, grain boundary sliding was observed. Its activation energy was about 94.8 kJ/mol. This value is close to that for the grain boundary diffusion of pure magnesium.

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Stress fluctuation, deformation band, and strain marking in a tensile deformed 5083 aluminum alloy plate at 318K were examined using an Instron tensile machine, a stylus surface profiler, and strain gauges; related temperature dependencies were also investigated. A saw-tooth stress fluctuation was generated in the nominal stress vs. nominal strain curves in two different deformation regions, a yield point region and a region advanced by plastic deformation. A surface profiler revealed that an intermittent formation of the deformation band, known as a parallel band, resulted in both a saw-tooth-like stress fluctuation and a stair-like strain increase. The temperature dependencies of stress fluctuation, deformation band, and strain marking indicated that changes from a wavy stress fluctuation to a saw-tooth-like one with increasing deformation temperature were due to a variation in the propagation velocity and a repetition of the intermittent formation of the deformation band.

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The present authors have found that the in-situ type composite of AlN plus Al can be formed by having Al react with powder BN and by fixing the weight ratio of the former to the later to a suitable value under a certain condition of heating temperature and pressurized atmosphere of N₂. The most recommended conditions for the reaction is such that heating at 1373 K under 1.013 MPa of N₂ with the mass ratio of Al to BN to 6 : 1. Volume fraction of AlN in the primary composite ingot is around 40%. If we secondarily heat-treat this composite under the suitable condition of higher temperature and higher pressure of N₂ than those for the primary composite, the volume fraction of AlN can be raised to a value more than 90%. The properties such as thermal expansion coefficient and hardness of this high ratio AlN composite are very close to those of the commercial AlN which is usually made by the sintering method. So, the present type of AlN+Al composite, which is expected to be produced at a low cost, may be used for such as the heat-sink substrate for semiconductor devices, and also may be used as the light weight heat-resisting material.

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Commercial 1050 aluminum sheets have been cold-rolled in vacuum, to obtain high friction between rolls and sheet. This cold-rolling in vacuum successfully introduced large shear deformation near the sheet surface. The type and sharpness of texture in layers and the degree of inhomogeneity depend mainly on the vacuum degree, that is to say, on the friction between rolls and the material. These high shear strains, which are caused by 37% reduction in thickness, are sufficient to produce so-called shear texture of which main components are {111} ‹110›, {112} ‹110› and {001} ‹110›. The typical features of vacuum-rolled textures are that the intensity of {111} ‹110› component is highly developed in the surface layer, and that the rotation around ‹111› axis or ‹111›//ND fiber is also observed there. {001} ‹100› cold-rolling texture is observed at the mid-thickness of the sheet.

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