Study of in situ formed quasicrystals in Al-Mn based alloys fabricated by SLM

Quasicrystal (QC) phases are often observed in Al-based alloys with Al content< 85 at%, and their particle size is typically greater than 0.3 µm. In this study, an in situ formed QC phase was observed in Al-4.1Mn-0.98Mg-0.8Sc-0.5Zr alloy (Al ≈ 96 at%) when processed using Selective Laser Melting (SLM). The particle size of the QC phase processed by SLM is 55–85% smaller than when processed by other methods, which is likely due to the lower Mn concentration and higher cooling rate. Moreover, the shape of the QC phase is spherical near the bottom of the melt pool and becomes a strip in the center of melt pool with the variation of solidification conditions. At higher cooling rates, it can be inferred that the formation of QCs is promoted while the growth of QC phase is effectively inhibited. According to calculations and electron spectroscopy (EDS) results, the possible chemical composition of the QC phase is considered as Al₈₀Cu_2.83Mn_17.16 (at%) with an e/a of 1.9849 and R_av of ~1.4152 Å. During aging, a portion of the QC phase could transform into Al₆Mn through a peritectoid reaction. The homogeneously dispersed QC transforms the Al₆Mn into a finer and more dispersed phase. Consequently, the mechanical properties are cooperatively improved both by Al₆Mn and the residual QC phase. After aging, the ultimate strength is 548.67 ± 4.66 MPa with an elongation of 12.2 ± 1.09%. These results indicate that SLM expands the formation range of QC and is an ideal processing route to fabricate in situ QC-strengthened Al-based alloys.