The Al-Mn-Sc-based alloys specific for additive manufacturing (AM) have been recently developed and can reach ultrahigh strength and adequate elongation. However, these alloys commonly exhibit non-uniform plasticity during tensile deformation, which is a critical issue hindering their wider application. In this work, the origin of this non-uniform plasticity of the alloys produced by laser powder bed fusion (LPBF) has been systematically investigated for the first time. The results show that the loss of uniform plasticity in the alloy originates from microstructural regions containing equiaxed fine-grains (FGs) (∼650 nm in size) at the bottom of the melt pools. In micro-tensile tests, the strength of these FG regions can reach a peak of ∼630 MPa. After this, an apparent yield drop occurs, followed by rapid strain softening. This FG behavior is associated with intermetallic particles along grain boundaries and a lack of uniform mobile dislocations during deformation. The columnar coarse-grain (CG) regions in the remaining melt pools show uniform plasticity and moderate work hardening. Furthermore, the quantitative calculations indicate that the solid solution strengthening in these two regions is similar. Nevertheless, secondary Al₃Sc precipitates contribute to ∼260 MPa strength in the FG, compared to 310 MPa in the CG due to their different number density. In addition, grain boundary strengthening can reach 230 MPa in the FG region; nearly double the CG region value.

最近开发了专用于增材制造 (AM) 的 Al-Mn-Sc 基合金，可以达到超高强度和足够的伸长率。然而，这些合金在拉伸变形过程中通常表现出不均匀的塑性，这是阻碍其更广泛应用的关键问题。在这项工作中，首次系统地研究了激光粉末床熔融 (LPBF) 生产的合金的这种非均匀塑性的起源。结果表明，合金中均匀塑性的丧失源于熔池底部含有等轴细晶粒 (FG)（尺寸约为 650 nm）的微观结构区域。在微拉伸试验中，这些 FG 区域的强度可以达到约 630 MPa 的峰值。在此之后，发生明显的屈服下降，随后是快速应变软化。这种 FG 行为与沿晶界的金属间粒子和变形过程中缺乏均匀的移动位错有关。其余熔池中的柱状粗晶 (CG) 区域显示出均匀的塑性和适度的加工硬化。此外，定量计算表明，这两个区域的固溶强化相似。尽管如此，二次铝由于数量密度不同，₃ Sc 沉淀物在 FG 中的强度约为 260 MPa，而在 CG 中为 310 MPa。此外，FG区域的晶界强化可达230 MPa；几乎是 CG 区域值的两倍。