Laser rescanning technology is usually used to improve the forming quality of 3D printed parts. In order to investigate the relationship between rescanning strategy and forming quality, this paper proposed an interlayer rescanning strategy, which scans once at each odd-number layer and rescans at each even-number layer. In this work, 3D printed parts with inner structures were manufactured via selective laser melting. White light interference profilometry, scanning electron microscope, and three coordinates were used to analyze the surface quality, overhang sinking distance, and therefore the performance of samples with rescanning. White light interference profilometry-based roughness characterization revealed that the minimum surface roughness measured was 8.338 µm with rescanning and 9.676 µm with interlayer rescanning. The range of overhang sinking distance varied to a minimum of 0.146 mm with rescanning and 0.318 mm with interlayer rescanning. Based on the force analysis of the molten pool of overhang layers, the overhang sinking was mainly due to the increasing gravity of the molten pool and the insufficient supporting force provided by lower layers.

A systematic work was studied to illustrate the influence of laser power on the forming quality of Al6061 alloy by selective laser melting (SLM). The relationship between laser power and molten pool was simulated by finite element analysis (FEA). Phase composition, defects, and microhardness were also measured and analyzed. The results show that, with the increase of laser power, the molten pool gradually changes from rectangular shape to droplet shape. And the cooling rate gradually increases from 3.282 × 104°C/s to 5.189 × 104°C/s. Higher laser power (400 W) is accompanied by higher molten pool maximum temperature (2012.73°C). This may lead to larger temperature gradient inside the sample causing evaporation and spatter of powder. On the contrary, lower laser power leads to unmelt of some powders, which increases the number of pore defects and influences the forming quality of samples. X-ray diffractogram (XRD) displays the Al6061 alloy characterized by the obvious preferred orientation under different laser powers and the grain size increased from 32.57 nm to 35.38 nm. With the increase of laser power, the number of defects, especially holes and microcracks, was first decreased and then increased. However, the microhardness of the sample decreased almost linearly from 98.6 HV0.05 to 88.86 HV0.05. All changes are the result of the comprehensive action of laser power and molten pool state. Besides, the action mechanism of laser power on the forming quality was also clarified in this work.