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

doi:10.1007/s40195-023-01553-4

Abstract

Abstract:

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.

Key words: Laser powder bed fusion, High strength aluminum alloy, Hot cracking, Single track

Xiaojia Nie, Ze Chen, Yang Qi, Hu Zhang, Haihong Zhu. Spreading Behavior and Hot Cracking Mechanism of Single Tracks in High Strength Al-Cu-Mg-Mn Alloy Fabricated by Laser Powder Bed Fusion[J]. Acta Metallurgica Sinica (English Letters), 2023, 36(9): 1454-1464.

Figures/Tables 12

Fig. 1 a Relationship between droplets temperature and solidification time, b relationship among solidification time, droplets temperature and scanning speed

Fig. 2 Schematic diagram of the size of the molten pool on XOY plane

Fig. 3 a Relationship between scanning speed and center temperature of molten pool, b relationship between scanning speed and characteristic length of molten pool

Fig. 4 Relationship between viscosity of a metal melt and temperature

Fig. 5 a Relationship between temperature and Ma, b relationship between scanning speed and Ma

Fig. 6 SEM images showing the top views of single tracks fabricated with different scanning speeds: a-f v = 83-500 mm/s, g-i v = 667-1000 mm/s

Fig. 7 Typical cross sections of single tracks: a v = 83 mm/s, b v = 333 mm/s, c v = 667 mm/s

Fig. 8 Cracks on the surface of a single track: a low magnification image, b partial enlarged drawing

Fig. 9 Liquid feeding channel calculated by JMatPro software: a Al-Cu-Mg-Mn alloy, b AlSi10Mg

Fig. 10 SEM image of cross section of single track fabricated at v = 333 mm/s

Fig. 11 Relationship between scanning speed and molten pool existence time

Fig. 12 Effect of temperature gradient G and growth rate R on the morphology and size of solidification microstructure

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