The effects of the final-aging condition and the step-quenching treatment on the two-step-aging behavior of a 6063 aluminum alloy were investigated mainly by tensile test together with electrical resistivity and differential scanning calorimetric (DSC) measurements. The results indicated that the clusters formed during the pre-aging treatment at a relatively low temperature for a long time had marked influence on the tensile properties after the two-step-aging treatment. The proof stress of the specimen aged at 413 K for 108 Ks after the pre-aging at 263 K for 604.8 Ks indicated a negative effect, i.e. the proof stress of the two-step-aged specimen fell down by about 40% than that of the specimen only aged at 413 K. It was suggested that this negative effect was caused by the decrease in the amount of β" phase formed in the final aging due to the retained clusters. The decrease in excess vacancies by the step quenching to around 410 K and holding for 1.0 Ks, suppressed effectively the formation of clusters during the pre-aging treatment, which would lead to prevent the negative effect of two-step-aging treatment.

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Magnesium alloys are remarkably corroded in chloride environments. The corrosion behavior of the AZ91 alloy is mainly dependent on Fe/Mn ratio and size and distribution of the intermetallic Al-Mn-Fe phase and Mg₁₇Al₁₂ (β-phases) particles. Grain size and heat-treatment condition also influence both the microstructure and corrosion behavior. The AZ91E was melted and casted into various permanent molds in order to obtained several cast ingots with different grain sizes (110 to 250 μm). Some ingots were heat-treated to control the distribution of β-phase particles. Corrosion characteristics were evaluated by a salt-water immersion testing and the open circuit corrosion potential measurement. Metallographic characteristics were evaluated by the average distance between intermetallic phase particles. The corrosion rate was increased with increasing the grain size in the as-cast (F) specimens. But it was independent of Fe/Mn ratio. Both of grain size and Fe/Mn ratio affected the corrosion behavior in the homogenized (T4) specimens. Independent of grain size and Fe/Mn ratio. Artificially aged (T6) specimens showed a good corrosion resistance. It was found that the β-phase act as a good barrier against salt-water corrosion. Corrosion potential of the Al-Mn-Fe phases depending on the composition.

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Possibilities of the consolidation process using hot extrusion were investigated in order to recycle the cutting chips of the aluminum alloy efficiently. Influences of the size and the cleanliness of the cutting chips and extruding conditions on mechanical properties and corrosion resistance of the recycled materials were examined to optimize the processing condition. Cutting chips were collected from 6061 aluminum alloy round bars using the lathe, and they were pretreated to prepare chips with different cleanliness. The cutting chips were forced into a pure aluminum can, and extruded under various extrusion ratios and temperatures. The obtained extrusions with T6 heat-treatment were defined as “Recycled materials”. Optical microscopic observation, EBSP analysis, tensile tests and immersion corrosion tests were carried out to the recycled materials. Mechanical properties and the corrosion resistance of the recycled materials were almost equivalent to the highest values of the virgin material. Higher extruding temperature was required in order to consolidate finer cutting chips. However, the recycled materials using fine chips showed improved strength parallel to the extrusion direction.

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In order to recycle machined chips, hot extrusion tests were performed on magnesium alloys AZ31B and AZ91D. Two types of extrusion dies were used—one with an exit corner having a sharp rectangular edge (N-die) and the other with an exit corner having a round edge (R-die); the radius of the round edge was 1.5 mm. In the extrusion tests using N-die, peculiar and wavy surface roughness that was almost perpendicular to the extrusion direction was formed in the extrusions obtained from machined chips of both the alloys. This roughness appears to be due to discontinuous metal flow caused by the basal plane slip along the exit corner of N-die. Therefore, the exit corner of R-die was essentially effective in improving the surface roughness of the extrusions because it led to smooth and continuous metal flow. The surface roughness tended to decrease with an increase in the extrusion ratio R from 19 to 100. Grain boundary sliding in the extrusion surface layer at the die exit appears to be a possible mechanism of another type of surface roughness, particularly in the extrusion tests performed with lower extrusion ratios, i.e., at lower strain rates.

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TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile tested in various environmental media as functions of temperature and strain rate. Environmental media used in this study were vacuum, air, water vapor, a mixture gas of 5 vol%H₂+Ar, O₂ gas, N₂ gas and Ar gas. All the TiAl-based intermetallic alloys showed low tensile strength or tensile elongation in air, water vapor and a mixture gas of 5 vol%H₂+Ar compared to those in vacuum. The reduction of tensile strength or tensile elongation (i.e. environmental embrittlement) was observed not only in low temperature range mostly reaching 600 K but also in high temperature range mostly from 600 K to 1000 K (sometimes temperatures higher than 1000 K). The low- and high-temperature environmental embrittlement depended on the alloy composition (or microstructure). The low-temperature environmental embrittlement diminished at higher strain rates. The high-temperature environmental embrittlement diminished not only at higher strain rates but also at lower strain rates. The possible species causing the high-temperature environmental embrittlement is hydrogen atoms decomposed from water vapor (H₂O) or hydrogen gas (H₂), similar to those causing the low-temperature environmental embrittlement. Also, it is suggested that the oxidized scale is effective in reducing the high-temperature environmental embrittlement.

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