To improve the forming efficiency of selective laser melting (SLM), this study systematically investigated the effects of high-energy process parameters (HEP) and low-energy process parameters (LEP) on the microstructure and mechanical properties of Al-4.8 Mg-0.7Sc-0.3Zr alloy under a constant energy density of 83 J/mm3. The results show that despite the same energy density, the melt pool size is significantly larger under HEP conditions, with columnar grains accounting for approximately 42.38% and their long-axis dimensions ranging from 7.32-32.11 μm, along with a strong \(\left\langle {001} \right\rangle\) \(//Z\) fiber texture (where Z denotes the building direction). In contrast, the melt pool is smaller under LEP conditions, the proportion of equiaxed grains increases to 69.11%, the long-axis dimensions of columnar grains are only 6.5-19.1 μm, and the texture intensity is significantly reduced. Mechanical property tests indicate that the LEP sample exhibits a tensile strength of 357.6 MPa, comparable to the 361.4 MPa of the HEP sample, while its elongation is significantly increased to 24.6%—surpassing the typical level of 15-20% for most Al-Mg alloys fabricated by SLM currently. After aging treatment, the strength of the A-LEP sample is further enhanced to 512.5 MPa. The core reason for the improved performance lies in the lower cooling rate under LEP conditions, which promotes the heterogeneous nucleation of Al3(Sc,Zr) nanoparticles. Combined with the smaller melt pool size and lower strain hardening rate, this collectively contributes to a more uniform microstructure and superior plastic coordination ability. This study clarifies the intrinsic mechanism of regulating melt pool characteristics and grain distribution through process parameter combinations under constant energy density, providing a new approach for the efficient and high-performance SLM forming of aluminum alloys.
