| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stringing beam body suppressing the growth of pitting deeply progressing to the inside of the material and maintaining excellent corrosion resistance and fatigue strength over an extremely long period. SOLUTION: In this stringing beam body, an extruded material having a compsn. contg. 0.65 to 0.75% Si, 0.60 to 0.70% Mg, 0.15 to 0.25% Fe, 0.12 to 0.18% Cu, 0.14 to 0.18% Mn, 0.05 to 0.09% Cr, 0.01 to 0.20% Ti, 0.0001 to 0.005% B, <=0.05% Zn, and the balance substantial Al with other impurities by <=0.10% in the total content, and in which, in the cross-section vertical to the extruding direction of the extruded material, excepting the recrystallized structure of <=150μm thickness generated on the surface of the extruded material, a fibrous structure is shown, and, in the cross-section parallel to the extruding direction of the extruded material, the part high in the concn. of Ti and the part low in the concn. of Ti extending to the extruding direction are laminated in layers is used.
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