アルミニウム合金の高温変形

摘要

アルミニウムの高温変形は，温度，ひずみ速度，ひず み量で分類することができる。工業的には，降伏応力以 下でのクリープと降伏応力以上での熱間加工（圧延，押 出，鍛造など）が重要である。また比較的低応力下で高 延性が得られる超塑性も工業的に利用される状況になっ ている。%Many studies have been reported about high temperature deformation, especially, creep, superplasticity and hot workability of hot rolling or extrusion in aluminum alloys. In this report, the basic concept and the evaluation of these phenomena are reviewed and our fruits of recent research and development about high temperature deformation of aluminum alloys are mainly introduced. In creep, the Al-Mn alloy extrusion with high creep resistance for heat roller in printing machines and the Al-Mn alloy sheet with high creep resistance for battery case of cellular phones are shown. In superplasticity, the characteristics of Al-Zn-Mg-Cu, Al-Li and Al-Mg superplastic alloys are reviewed. In particular, recently, Al-Mg superplastic alloys are used for automotive body panels because these sheets are dynamically recrystallized during deformation in high strain rate. In hot working, the recent evaluation method of workability and our results are summarized. Intermediate thermomechanical treatment is effective in improving the mechanical properties or the stress corrosion resistance in hot rolled plate of high strength aluminum alloys because of reducing the grain boundaries of ingots. In warm rolling, it is found that the subgrains with thermal stability are obtained by rolling at a constant temperature and the sheet with these subgrains shows high stress corrosion resistance or high Lankford value. In extrusion, the microstructures of extrusions, that is, recrystallized, fibrous or their mixed structures depend on homogenizing conditions which change the dispersion of second phase particles and the content of solute atoms. In high strength aluminum alloys, such as Al-Zn-Mg-Cu alloys, it is found that precipitation control in homogenizing process is effective to reducing the flow stress and increasing extrudability, and further reducing the grain growth near the surface of extrusions. Finally, hot tearing about high purity aluminum and Al-Mg alloys is shown. In future, quantitative analysis of structural change during hot working would be required for microstructural control.