高温加熱時のAl-Fe-si合金中の縦ノ木組織の挙動

This study was made to investigate the change of "fir-tree" structure in D. C. cast Al-Fe-Si alloys during heating at elevated temperatures.The specimens used were Al-0.6%Fe and Al-0.6%Fe-0.1%Si alloy, some of which had been hot-rolled or cold-rolled. They were soaked at several temperatures of 560640°C.The experiments were carried out by anodizing, X-ray diffraction, optical microscopy, and electron microscopy.The results obtained were summarized as follows:(1) FeAl3 phase was present in the inner region of "fir-tree" structurs, while FeAl3 phase was found in the outer region. Another unknown phase would possibly be present in the outer region.(2) The "fir-tree" structure was eliminated by the transformation of FeAl6 into FeAl3 during heating at elevated temperatures.(3) The relation between the time required to eliminate the "fir-tree" structure and the reciprocal of the temperature conformed to Arrhenius' equation. The activation energy was evaluated to be 75 kcal/mol from the slope of the equation. The activation energy depended neither on the presence of 0.1%Si, nor on plastic deformation.(4) The following two processes were observed by heating thin foils in an elctron microscope.One was dissolution of FeAl6 phase in matrix and precipitation of FeAl3 phase on grain boundaries. The other was transformation of FeAl6 into FeAl3 in place, though the exact position of nucleation could not be determined.(5) Being derived from the above-mentioned activation energy, the rate determining step of the transformation seemed to be the diffusion of Fe or Al in the intermetallic compounds.