The Effect of Thermal Cycle on Hot Cracking Evolution and Formation Mechanism in Thin Wall, Single Layer, and Cubic Samples of High-Strength Al-Cu-Mg-Mn Alloys Fabricated by Laser Powder Bed Fusion.

Thermal cracking is one of the serious issues that deteriorates the processibility of laser powder bed fusion (LPBF) high-strength aluminum components. To date, the effects of processing parameters on crack formation are still not well understood. The purpose of this study is to understand the correlation between the thermal cycle and the hot cracking during LPBF of Al-Cu-Mg-Mn alloys. In this study, we performed a detailed microstructural and morphogical characterization of molten pool to explain the initiation, propagation, and arrest of hot cracking. Thin wall, single layer, and cubic samples with different processing parameters were selected for an in-depth study of thermal cycling. Under the action of single vertical thermal cycling, the solidification crack at the center of the molten pool will heal, but the solidification cracks at the boundary of the molten pool still exist. Under the action of single horizontal thermal cycling, the initiation point and propagation path of solidification cracks are formed at the overlap zone of molten pool. However, under the alternating action of horizontal and vertical thermal cycles, the crack would not disappear, but would always exist and propagate through the multilayer. Adjusting the processing parameters, which could provide preheating, increase the amount of liquid phase, reduce the residual stress, extend the lifetime of the molten pool, and refine the grain size will decrease the hot cracking susceptibility of LPBFed Al-Cu-Mg-Mn alloys.