稀土元素Ce对Al-Cu-Mn-Mg合金显微组织及力学性能的影响

Influence of Ce Addition on Microstructure and Mechanical Properties of Al-Cu-Mn-Mg Alloy

摘要:

采用OM、SEM、TEM及XRD等表征技术研究了微量Ce对Al-Cu-Mn-Mg合金显微组织与力学性能的影响。结果表明：随着Ce含量的增加，合金中会形成两种不同的含Ce化合物，一种是凝固过程中形成的初生Al₂₀Ti₂Ce相，该相的出现消耗了Al熔体中有效的晶粒细化元素Ti，导致合金的晶粒粗化。另一种是凝固后期通过共晶反应形成的Al₁₆Cu₄Mn₂Ce相，该相在高温下不稳定，热处理过程中会转变为Al₂₄Ce₃Cu₈Mn和Al₂₀Cu₂Mn₃，无法使Al₁₆Cu₄Mn₂Ce相中的Cu、Mn元素固溶入Al基体，导致热处理后合金基体中Cu、Mn元素的过饱和度下降。此外，Ce的添加会延缓Al基体中θ′′相向θ′相的转变过程，同等热处理条件下，含Ce合金的Al基体中的主要强化相为θ″，而不含Ce合金中的强化相为θ′。稀土元素Ce对合金相组成及显微组织的影响直接体现在合金力学性能的变化上，当Ce含量由0wt%增加至0.3wt%时，与不含Ce的基础合金相比，含0.3wt% Ce合金的极限抗拉强度和屈服强度分别下降了95.0和45.5 MPa，伸长率下降了约50%。

Abstract:

This study systematically investigated the influence of cerium (Ce) addition on the microstructure and mechanical properties of Al-Cu-Mn-Mg alloys through multi-scale characterization techniques, including OM, SEM, TEM, and XRD. The results reveal that the addition of Ce leads to the formation of two distinct Ce-containing intermetallic compounds. One is the primary Al₂₀Ti₂Ce phase formed during solidification, which induces grain coarsening by consuming the effective grain-refining element Ti in the melt. The other Ce-containing phase is Al₁₆Cu₄Mn₂Ce, which forms through a eutectic reaction at the final stage of the solidification process. Unlike Al₂Cu, this phase is unstable at high temperatures and undergoes transformation into Al₂₄Ce₃Cu₈Mn and Al₂₀Cu₂Mn₃ during heat treatment. Consequently, Cu and Mn from Al₁₆Cu₄Mn₂Ce phase cannot dissolve into the Al matrix, resulting in a reduction in supersaturation degree. Furthermore, the minor addition of Ce retards the phase transformation from θ′′ to θ′ in the Al matrix. Thus, with the identical heat treatment, the primary strengthening phase is θ′′ phase in the Ce-containing alloy, whereas the strengthening phase is θ′ phase in the alloy without Ce addition. These changes in the microstructure and phase composition directly influence the mechanical properties of alloys: with Ce content increasing from 0wt% to 0.3wt%, the ultimate tensile strength and yield strength are decreased by 95.0 and 45.5 MPa, respectively, and the elongation is reduced by about 50%, compared with those counterparts of the alloy without Ce addition.