Crack mitigation strategies for a high-strength Al alloy Al92Ti2Fe2Co2Ni2 fabricated by additive manufacturing

Abstract

Laser powder bed fusion is capable of fabricating aluminum (Al) alloy parts with great geometrical flexibility and rapid prototyping for various industries. However, high strength Al alloys generally suffer from solidification cracks due to the steep thermal gradient associated with the laser fusion process. Here, we report several strategies to mitigate the hot crack susceptibility of a high strength Al92Ti2Fe2Co2Ni2 alloy. Routine processing parameter optimization based on varying laser power and scanning speed has to trade off porosity for producing crack-free parts, making it not suitable for load-bearing structural applications. Furthermore, secondary printing parameters, including laser strip length, laser defocus, scanning strategies, etc., improved printability but were insufficient to eliminate all the cracks. Crack morphology and residual stress measurements indicate that the cracks are generated in the solid state driven by large tensile residual stress, instead of solidification cracking or liquation cracking. Thus, an attempt was made to alleviate the residual stress in a controlled manner. By properly introducing a compliant, sacrificial, scaffold support structure to regulate crack propagation, near fully dense, crack-free parts could be successfully printed. The results were further verified by micro computed tomography, showing that cracking could be arrested in the support before propagating through the parts. This method can be readily applied to other alloy systems without modifying the chemistry.