Spreading Behavior and Hot Cracking Mechanism of Single Tracks in High Strength Al-Cu-Mg-Mn Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) technology is a high-precision metal additive manufacturing (AM) technology. Due to the high specific strength of high strength aluminum alloys, high strength aluminum alloys fabricated by LPBF have broad application prospects in the field of light weighting. However, high strength aluminum alloys have high hot cracking susceptibility. In this study, an analysis of the hot cracking susceptibility as a function of processing parameters is presented for single tracks of LPBF processed (LPBFed) high strength Al-Cu-Mg-Mn alloy. The hot cracking in single tracks of LPBFed Al-Cu-Mg-Mn alloy is solidification cracking based on the experimental observations of microstructure. Combining Rosenthal simulations and spreading behavior of a single droplet, the critical scanning speed of single track with balling phenomenon was obtained. It was found that when the laser power was 200 W, the scanning speed exceeded 440.1 mm/s, the droplet will not be able to spread completely, which is consistent with the experimental result of 500 mm/s. Through the calculation and analysis of the microstructure and the existence time of the molten pool, it was pointed out that the reduction in the liquid phase caused by the high scanning speed, the shortening of the solidification time and the high stress caused by the high-temperature gradient promoted the generation of hot cracking. In summary, this work contains a practical guide to optimize processing parameters of LPBFed Al-Cu-Mg-Mn alloys, which provides a basis for fabricating thin walls and cubic samples without hot cracking.