Characteristics of ZrAl intermetallic crystals during solidification of aluminum wrought alloys

在铝变形合金中经常添加锆，以细化晶粒，提高强度并提供更好的抗再结晶能力。然而，Zr的加入可能会导致不良的锆金属间晶体的析出，并在铸造产品中引起一些与铸造工艺相关的问题和缺陷。在某些情况下，Zr与其他合金元素（Fe、V、Ti和B）的相互作用以及Zr对Ti和TiB2晶粒细化的毒害作用对最终产品的性能有很大的不利影响。本研究的主要目的是为了更好地了解锆及其金属间化合物对制备工艺和最终产品性能的影响。利用热力学计算和受控条件下的物理实验，研究了典型7xxx合金中锆金属间化合物的形成和锆的溶解度极限。采用光学金相、扫描电镜和透射电镜研究Zr水平和冷却条件对锆金属间晶体的成核、生长和形貌的影响。系统研究Zr与其它合金元素（Fe、V、Ti和B）在金属间形成、晶粒细化和抗再结晶方面的相互作用机理。在对典型合金中的锆金属间化合物进行表征后，本研究将通过7xxx系列合金家族分析含锆金属间化合物对材料性能的影响，并对所得材料性能进行评价。通过本研究获得的信息可以极大地帮助铝工业提高许多重要变形合金的生产率和产品质量。

Zirconium is often added in aluminum wrought alloys to refine the grains, increase the strength and provide a better resistance to recrystallization. However, the addition of Zr may lead to the precipitation of undesirable zirconium intermetallic crystals and cause a number of casting process related problems and defects in the cast products. It is observed in some cases that interaction of Zr with other alloying elements (Fe, V, Ti and B) and poisoning effect of Zr on the Ti and TiB2 grain refinement have a great detrimental effect on the properties of final products. The main objective of this study is to better understand the effect of zirconium and its intermetallics on the fabrication processes and final product properties. Using thermodynamic calculation and physical experiments under controlled conditions, the formation of zirconium intermetallics and the solubility limit of zirconium in a typical 7xxx alloy will be investigated. The impact of the Zr level and the cooling condition on the nucleation, growth and morphology of zirconium intermetallic crystals will be examined using optical metallography and scanning and transmission electron microscopes. The mechanisms of the interaction of Zr with other alloying elements (Fe, V, Ti and B) in term of intermetallic formation, grain refinement and anti-recrystallization will be systematically studied. After the characterization of zirconium intermetallics in a typical alloy, the research will go through the 7xxx series alloy family to analyze the impact of complex Zr bearing intermetallics and to evaluate the resulted material properties. The information gained through this study can greatly help the aluminum industry to enhance the productivity and product quality for a number of important wrought alloys.