Additively manufactured AlSi10Mg ultrathin walls: Microstructure and nano-mechanical properties under different energy densities and interlayer cooling times

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. • Characteristics and formation mechanism of sandwich-like microstructure in SLM AlSi10Mg ultrathin walls were explained. • Response of local mechanical properties associated with the alternating changed “sandwich” microstructure was revealed. • Interaction between various strengthening mechanisms comprehensively affects the nano-mechanical properties.