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

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.