Effect of laser power on the forming quality of Al6061 alloy manufactured via selective laser melting

Abstract

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.