| 摘要 |
PROBLEM TO BE SOLVED: To prevent the development of a crank on a rib even in the case of using an aluminum alloy seriously taking the castability by forming the ratio of a cross sectional area of the rib and a peripheral length of the rib in a blank for forging to a specific value. SOLUTION: The casting is executed to the shape having >=1.99 A/L of the cross sectional area A (mm<2> ) of the rib and the peripheral length L (mm) in the blank for forging. Further, the casting is executed to the shape having >=3mm, desirably >=4mm curvature radius Rr at the rising part of the rib, and >=1mm, desirably >=3mm curvature radius Rt at the top part of the rib, and >=5 deg., desirably >=8 deg. draft angleθof the rib. In the case of matching the shape of the casting blank to these conditions, the fluidity of the rib part is improved and the casting defect is not developed. The crank on the rib is developed as the starting point in the case of developing such casting defect as the abnormal structure having Si segregation. Even in the case of using the aluminum alloy for casting and forging deteriorated in the fluidity by seriously taking the forgeability, the crank on the rib in the forging process does not come to develop.
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