纳米AlP变质加高压凝固制备高韧性过共晶铝硅合金基础研究

The Phosphorus modification is the stable and practical method to refine the primary Si in the hypereutectic Al-Si alloy. The primary Si can be refined to 20 μm, but there is no substantial progress in the improvement of its toughness. The fundamental reasons are that the size of AlP as nucleation substrate is too large to get the smaller primary Si, and that the amount of α phase is small and that of the lamellar eutectic Si is large between the primary Si. So the project applicant proposes the method of preparing hypereutectic Al-Si alloy by nano AlP modification and high pressure solidification. The researches are as follows: (1) The forming process and control technology of nano AlP particles; (2) The forming conditions of the hyperfine primary Si; (3) The influence of pressure on the formation of α phase around the hyperfine primary Si. (4) The crack expansion process in the microstructure of α phase and hyperfine primary Si . (5) The relationship between the morphology and amount of α phase and the elongation of the hypereutectic Al-Si alloy. The key scientific problems lie in making sure the dynamic condition of forming nano AlP particles and the forming process of the microstructure of the primary Si surrounded by α phase under high pressure. The research has practical significance and research value for finding the new way of improving the toughness of the hypereutectic Al-Si alloy and achieving high toughness. Moreover, the research also has important scientific significance for exploring the forming processes of the nucleation substrate of in-situ nanoscale primary Si and single α phase transformed by the residual melt in Al liquid.

细化过共晶铝硅合金初生硅效果稳定且实用的方法是磷变质处理，虽然可使初生硅细化到20μm，但韧性的提高却无实质性进展，其根本原因是作为形核基底的AlP尺寸过大无法得到更细的初生硅、初生硅之间α相数量少且片状共晶硅数量多。为此本项目提出了纳米AlP变质加高压凝固制备高韧性过共晶铝硅合金的方法。主要研究(1)铝液中纳米AlP颗粒形成过程与控制技术；(2)超细初生硅形的成条件；(3)压力对超细初生硅周围α相形成的影响；(4)裂纹在α+超细初生硅组织中扩展过程；(5)过共晶铝硅合金中α相的形态和数量与延伸率对应关系等基础问题，以解决铝液内形成纳米AlP颗粒的动力学条件、高压条件下α相包围初生硅组织形成过程的关键科学问题。研究对于探索提高过共晶铝硅合金韧性的新途径并使其获得高韧性具有实际意义与研究价值；探索在铝液内自生纳米级初生硅形核基底、初生硅之间剩余熔体转变成单一α相的形成过程都具有重要科学意义。

P变质时，作为硅相形核基底的AlP尺寸过大无法得到更细的初生硅，加之片状共晶硅为裂纹扩展通道，导致过共晶铝硅合金韧性的提高无实质性进展。.主要研究内容：.Cu-P合金在铝液内的溶解以及自生纳米AlP颗粒形成机理研究；Al-Si合金无共晶硅凝固组织与超细初生硅形成机理与条件的研究；过共晶铝硅合金裂纹扩展过程的研究；磷化铝片剂与纯铝制备Al-P合金的研究；过共晶铝硅合金中硅相与延伸率对应关系的研究。.研究取得了以下重要结果：.（1）Cu-P合金在铝液内溶解过程以及铝液内自生纳米AlP颗粒形成机理。.固态Cu-P合金与铝熔体接触后，首先是表面上的αCu溶解、共晶Cu3P脱落，当Cu-P合金表面形成单相Cu3P后，溶解速度很慢。.Cu-P合金向铝液释放的P原子与Al形成AlP，其尺寸只是几个纳米，熔体搅拌使其立刻离开Cu-P合金颗粒周围的富P区，获得最小尺寸约为10nm的自生AlP颗粒。.（2）Al-Si合金无共晶硅凝固组织形成条件。700℃下加入Cu-P合金，用200r/min的速度搅拌20分钟，当Al-Si合金中Si含量大于10wt%、冷却速度大于16.3K/s时，可得到αAl基底上均匀分布13.1μm初生硅的无共晶硅凝固组织。.（3）过共晶Al-Si合金裂纹扩展过程。裂纹主要在初生硅平直边界处形成，而后在初生硅内直线扩展，在基体内的扩展方向与外力垂直，裂纹将共晶硅冲断后沿共晶硅/基体界面扩展。裂纹在初生硅与基体内扩展速度分别为37μm/s和0.9μm/s。.（4）以工业纯铝与磷化铝片剂为原料材料，用液淬与雾化法可制备出8mm颗粒状和粉末状Al-P合金。变质Al-18%Si合金后其延伸率达9.1%。.科学意义：.揭示了Cu-P合金在铝液内溶解过程以及自生纳米AlP颗粒形成机理、Al-Si合金无共晶硅凝固组织形成机理与条件。弄清了过共晶铝硅合金裂纹扩展行为，明确了Al-P合金中AlP颗粒尺寸的调控机制。