For additive manufacturing (AM) applications of lightweight aluminum alloy parts such as radiators, it is necessary to understand the relationship between internal microstructure and local mechanical properties. The microstructure characteristics and its formation mechanism of AlSi10Mg ultrathin walls fabricated by selective laser melting (SLM) under different energy densities and interlayer cooling times were investigated, and its evolution regularity with energy density was also analyzed. The nano-mechanical properties of different regions on the ultrathin-walled cross-section and their responses with energy density were also explored. The main results show that non-banding regions and banding regions distributed alternately like sandwiches are formed in ultrathin walls, which have fine solidified cellular structure and columnar dendrite network, accompanied by nano-scale substructure formed in grains. Although the microstructure characteristics and nano-mechanical properties of ultrathin walls are insensitive to interlayer cooling time, the single-track energy density significantly affects the coarsening of solidification structure and its substructure evolution. With the increase of single-track energy density, the interaction between various strengthening mechanisms related to the evolution of microstructure comprehensively affects the nano-hardness of different macro-areas in ultrathin walls, which follows the trend of increasing first and then decreasing, and higher nano-hardness can be obtained when the dimensionless single-track energy density is between 10 and 20. The findings of this work are beneficial to optimize the SLM process of AlSi10Mg alloy to manufacture ultrathin-walled parts with ideal microstructure and mechanical properties for potential applications in aerospace, automotive and other fields.

对于散热器等轻质铝合金零件的增材制造 (AM) 应用，有必要了解内部微观结构与局部机械性能之间的关系。研究了不同能量密度和层间冷却时间下选区激光熔化（SLM）AlSi10Mg超薄壁的组织特征及其形成机制，并分析了其随能量密度的演变规律。还探讨了超薄壁截面上不同区域的纳米力学特性及其对能量密度的响应。主要结果表明，非条带区和条带区呈三明治状交替分布在超薄壁中，具有精细的凝固蜂窝结构和柱状枝晶网络，伴随着晶粒中形成的纳米级亚结构。虽然超薄壁的微观结构特征和纳米力学性能对层间冷却时间不敏感，但单道能量密度显着影响凝固组织的粗化及其亚结构演化。随着单道能量密度的增加，与显微组织演化相关的各种强化机制之间的相互作用综合影响了超薄壁不同宏观区域的纳米硬度，呈现先增大后减小的趋势。无量纲单道能量密度在10~20之间可获得纳米硬度。