求翻译：冷却速度不但影响亚共晶Al-Si合金的树枝晶结构，而且对枝晶间的亚共晶组织也有明显的影响。较快的冷却速度使α-Al相先于亚共晶硅组织形核生长，导致金属液中硅含量升高，从而改变了铝硅亚共晶合金的凝固组织形态。在一定冷却速度范围内，冷速的增加有助于细化晶粒，改善铸件表面质量，减少缩松缩孔、气孔等缺陷的形成倾向，提高合金强度，从而提高了合金的综合力学性能。是什么意思？

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Not only cooling rate influence hypo-eutectic Al-Si alloy dentrite structure, moreover also has the obvious influence to the interdendritic hypo-eutectic organization.The quick cooling rate causes α-Al to be before the hypo-eutectic silicon organization shape nucleus to grow, causes in the molten me