在半连续铸造过程中施加超声,成功制备了φ1250 mm 2219铝合金铸锭.利用光学显微镜、扫描电镜、能谱仪及直读光谱仪等仪器对铸锭的组织与成分分布进行检测与分析,探究超声对铸锭组织与偏析的内在作用机制.研究结果表明:超声振动引起的空化和声流效应能明显均匀组织结构,细化晶粒,尤其是心部晶粒细化率达到39.6%.超声促进铸锭晶间第二相呈枝丫状断续分布,晶内析出物点状弥散分布.同时,超声有效减小近表面负偏析,降低边部与心部之间的溶质浓度差异,弱化整个横截面的浓度波动,从而改善宏观偏析
1 Preliminary 11 Introduction 12 Cardinality 13 Topology of the Euclidean space 14 Metric space and Baire Category theorem 15 Continuous functions and Distance in metric space 151 Hausdorff distance and Gromov-Hausdorff distance 152 Invariant of domain 2 Lebesgue measure 21 Exterior measure 22 Measure 23 Borel sets and Measurable sets 24 Linear transformation of measurable sets 25 Sets of positive measure 3 Measurable functions 31 Measurable functions 32 Simple functions 33 Littlewood’s Three principles 4 Lebesgue’s integration theory 41 Integration 42 Interchanging limits with integrals 43 Lebesgue vs Riemann 44 Fubini’s Theorem 5 Differentiation 51 Monotone functions 52 Fundamental theorem of Calculus I 521 A detour: Bounded variation functions 53 Fundamental theorem of Calculus II 54 Lebesgue Differentiation Theorem 6 Function spaces 61 L P spaces 611 Normed vector space 612 A detour: Convexity and Jensen’s inequality 613 Completeness: Banach space 614 Separability 62 Hilbert space: