Length Scale of the Dendritic Array Tailoring Strength of a 5052 Aluminum Alloy

The present research aims to characterize 5xxx alloy series, considering chemistries based on the commercial 5052 alloy with three Mg contents (2.4wt.%, 2.6wt.% and 3.2wt.%) through transient directional solidification experiments. Very representative incoming impurities to a given twin-roll casting procedure were reached. As such, the Si, Fe, Cu, Mn and Cr-contents in the tested samples typically trend in between the suitable alloying spectrum. Microstructural analyzes were performed using polarized light microscopy of samples taken from various ingot positions. Growth relationships between the secondary dendritic spacing (λ2) and the growth velocity were determined. The 5052 alloys containing higher Mg content may induce a decrease in λ2 for a certain growth velocity. The hardness values measured across the three directionally solidified castings were directly related to the λ2, which can be considered a fundamental variable affecting mechanical strength. For representative conditions vis-à-vis those employed in industry, it was shown that even relatively small changes in Mg content of the 5052 alloy may have some impact on λ2. These results open new ways to predict the final as-cast microstructure characterizing commercial 5052 alloy products, with a view to controlling not only the dendritic growth but also the Mg content during casting operations.

本研究旨在通过瞬态定向凝固实验，对以商用5052合金为基础、设置三种镁（Mg）含量（2.4wt.%、2.6wt.%与3.2wt.%）的5xxx系合金（5xxx alloy series）开展性能表征。实验试样的杂质水平贴合双辊连铸（twin-roll casting）工艺的典型来料杂质特征，其中硅（Si）、铁（Fe）、铜（Cu）、锰（Mn）与铬（Cr）的含量均处于适宜的合金成分区间内。研究对从铸锭不同部位截取的试样采用偏光显微镜（polarized light microscopy）开展微观组织分析，明确了二次枝晶间距（secondary dendritic spacing, λ2）与生长速率之间的关联规律。结果表明，在特定生长速率下，镁含量更高的5052合金会导致λ2降低；三组定向凝固铸锭的硬度测试值与λ2直接相关，而λ2可被视为影响力学强度的核心变量。在贴合工业生产的典型工艺条件下，5052合金的镁含量即使发生小幅变化，也会对λ2产生一定影响。本研究结果为预测商用5052合金产品的最终铸态微观组织提供了新途径，有望在铸造作业中同时调控枝晶生长与镁含量。