Effectively mitigated macro-segregation and improved tensile properties of twin-roll cast Al–Mg–Si (6022) alloy strips via Zr addition
Effectively mitigated macro-segregation and improved tensile properties of twin-roll cast Al–Mg–Si (6022) alloy strips via Zr addition
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DOI：
10.1016/j.msea.2023.145318
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发表时间：
2023-07
期刊：
影响因子：
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通讯作者：
M. Zhang;H. Ning;Cheng Wang;K. Guan;Xuan Wang;Zhi-Gang Li;Hong Wang
中科院分区：
文献类型：
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作者：
M. Zhang;H. Ning;Cheng Wang;K. Guan;Xuan Wang;Zhi-Gang Li;Hong Wang
在双辊铸轧过程中，如何避免中心宏观偏析是一个很大的挑战，它严重限制了6xxx系列铝合金的力学性能。研究发现，在Al-1.0Mg-1.2Si（6022）合金中添加0.08wt%的Zr能有效地促进柱状晶向等轴晶的转变，细化凝固组织（尤其是α-Al枝晶和π-AlFeMgSi相）。更重要的是，铸态TRC带材的宏观偏析随着Zr的添加而得到很好的缓解。引入Zr元素后，α-Al枝晶和π-AlFeMgSi相的细化可能是由于（Al，Si）3 Zr相的形成，该相可作为α-Al枝晶和π-AlFeMgSi相的异质形核中心。中心区域的二次枝晶臂间距（SDAS）由原来的0.33 μ m减小到0.16 μm，有利于更多的溶质元素进入Al基体，从而提高Mg（kMg）和Si（kSi）元素的分配系数。因此，在凝固的最后阶段，在残余液相中有较少的溶质原子，导致中心宏观偏析的缓解。铸态、固溶处理（T4）和烤漆处理（T6）合金的拉伸性能随着Zr的加入而同步优化。特别地，T4合金的断裂延伸率从0.309%增加到0.334%，表明优异的可成形性。T6合金的屈服强度从227 MPa提高到239 MPa，满足更苛刻的使用要求。本研究为TRC工艺有效控制宏观偏析、生产高性能合金板带提供了一种策略。
It is a great challenge to avoid the central macro-segregation during the solidification process of twin-roll casting (TRC), which seriously limits the mechanical properties of 6xxx series Al alloys. In this study, we find that the trace addition of 0.08 wt% Zr to Al-1.0Mg-1.2Si (6022) alloy can effectively promote the columnar-to-equiaxed transition and refine the solidification microstructure (particularly α-Al dendrites and π-AlFeMgSi phase). More importantly, the macro-segregation of the as-cast TRC strip is well mitigated with Zr addition. The refinement of α-Al dendrites and π-AlFeMgSi phase may be attributed to the formation of (Al, Si)3Zr phases when introducing Zr element, which can act as heterogeneous nucleation sites for both of them. The secondary dendrite arm spacing (SDAS) in the central region of strips is sharply decreased from ∼33 to ∼16 μm, which facilitates the incorporation of more solute elements into the Al matrix, thus increasing the partition coefficients of Mg (kMg) and Si (kSi) elements. As a result, there are fewer solute atoms in the residual liquid phase during the final stage of solidification, leading to the alleviation of central macrosegregation. The tensile properties of the as-cast, solid solution treated (T4) and paint baking treated (T6) alloys are synchronously optimized with Zr addition. In particular, the fracture elongation of the T4 alloy is increased from ∼30.9% to ∼33.4%, indicating excellent formability. The yield strength of the T6 alloys is increased from ∼227 MPa to ∼239 MPa, satisfying the more demanding service requirements. This work can provide a strategy for the effective control of macro-segregation and produce alloy strips with high performance by the TRC process.