The effect of forging passes on the refinement of high purity aluminum during multi-forging was investigated. The attention was focused on the structure uniformity due to deformation uniformity and the grain refinement limitation with very high strains. The results show that the fine grain zone in the center of sample expands gradually with the increase of forging passes. When the forging passes reach 6, an X-shape fine grain zone is initially formed. With a further increase of the passes, this X-shape zone tends to spread the whole sample. Limitation in the structural refinement is observed with increasing strains during multi-forging process at the room temperature. The grains size in the center is refined to a certain size （110 μm as forging passes reach 12, and there is no further grain refinement in the center with increasing the forging passes to 24. However, the size of the coarse grains near the surface is continuously decreased with increasing the forging passes to 24.
Hot-rolled Fe-（0.75-2.20）Si （mass%） alloys were oxidized in dry air at 600-1200 ℃. The oxidation process was carried out by thermal gravimetric analysis （TGA）. At 600- 1 150 ℃, oxidation gain curves were approximately parabolic. Electron probe mieroanalysis （EPMA） was applied to investigate cross-section morphology of oxide layer and element distribution across the layer. At lower temperature of 700 ℃, the oxide layer consisted of internal oxidation zone （IOZ）, inner Si-rich layer （conglomerate of fayalite and magnetite） and outer hematite layer, while at higher temperature of 1200 ℃, fayalite and wustite were observed in external oxide scale. Liquidus temperature of fayalite was detected by differential scanning calorimetry （DSC）. Through comparing the oxidation mass gain and parabolic rate constant of the alloys, it was found that oxidation resistance of Fe-Si alloy was enhanced by increasing Si content below 1 150 ℃ while increasing Si content of the alloy resulted in higher oxidation rate above 1150 ℃ owing to the liquid fayalite formation.
Xiao-jiang LIUYong-quan HEGuang-ming CAOTao JIATeng-zhi WUZhen-yu LIU
