对Al-xCu (x=30, 40, 45, 50, 质量分数, %)合金凝固组织进行了系统的观察. 结果表明, 随合金中Cu含量由30% (质量分数, 下同)增加到50%, 合金中初生Al2Cu相形貌由枝晶状逐渐转变为棱面状, 表明Al2Cu相的生长方式由非小平面生长转变为小平面生长. 冷却速率对初生Al2Cu相生长形貌具有重要影响, 冷却速率较低时, 初生Al2Cu相为规则的棱面状; 随着冷却速率增大, 初生Al2Cu相逐渐转变为不规则的非棱面状, 表明Al2Cu相的生长方式由小平面生长转变为非小平面生长. 对凝固过程中初生Al2Cu相形貌转变研究发现, Cu含量为45%时, 初生Al2Cu相形貌由枝晶状向方形转变; Cu含量增加到50%时, 初生Al2Cu相形貌由枝晶状转变为网状.
Intermetallic compounds have unique natures. Due to the natures of high temperature resistance, high strength and high hardness, intermetallic compounds always exist as strengthening phase in many alloys. The primary Al2Cu phase in Al-Cu alloys is an intermetallic phase. The morphology, size and distribution of intermetallic compounds phases have largely effects on the mechanical properties of materials. Morphological evolution of intermetallic compounds is necessarily theoretical basis for controlling the size, morphology and improving the performance of intermetallic compound materials in the solidification process. At present, there are many reports on the research of Al-Cu alloys, the main research is focused on the eutectic point and 4.7%Cu (mass fraction) of Al-Cu alloys, but other composition alloys are less considered. The growth mechanism of Al2Cu phase and the primary Al2Cu phase structure of Al-Cu alloy are studied recently. However, the specific growth mechanism of Al2Cu phase is currently not very clear. Alloy composition and cooling rate are often encountered in the ordinary metal melting and solidification. The change of solidification conditions will lead to the transformation of heat and solute in the melt, which will form different morphologies. In this work, the effect of alloy composition and cooling rate on the morphologies and growth behavior of Al2Cu phase in Al-Cu alloys was studied. Through the microstructure observation of Al-xCu (x=30, 40, 45, 50, mass fraction) alloys, it was found that primary Al2Cu phase morphologies transformed from dendritic shape to regular bulk with the Cu content increased from 30% (mass fraction) to 50% in the alloy, which indicated that Al2Cu phase growth changed from non-faceted growth to faceted growth. Cooling rate also had a vital influence on primary Al2Cu phase morphologies. Under low cooling rate, primary Al2Cu phase morphologies were regular bulk. The morphologies of primaryAl2Cu phases were transformed into dendritic shape with the increasing of cooling rate. The specific morphology transformation rule of primary Al2Cu phases in Al-Cu alloys was also studied in the solidification process. It was found that when Cu content was 45%, the morphology transformation of primary Al2Cu phases was from dendritic shape to square morphologies. While when Cu content was increased to 50%, the morphology transformation of primary Al2Cu phases was from dendritic shape to reticular morphologies.
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