According to the material nature, aluminum alloys are widely applied in aerospace, construction, and automotive applications due to their characteristics of being lightweight, having good formability, and having good corrosion resistance. To further improve the degree of the lightweight quality, introducing a new material with high specific strength and a structure with a lightweight design would be efficient. Scalmalloy (Al-4.49Mg-0.71Sc-0.51Mn-0.27Zr-0.07Fe-0.03Si alloy), which exhibits high specific strength and is made by a 3D printing process with less design limitation, has huge application potential. In this study, the selective laser melting (SLM) process was introduced for sample preparation. Through XRD, EBSD, and TEM, the microstructure of the heat-treated samples at 325 °C with different heat-treatment times was analyzed to evaluate the optimized heat-treatment parameter for 3D printed Scalmalloy. The relationship between the mechanical properties and the variation of precipitation size and volume fraction is discussed in detail in this study.