Effective inhibition of hot cracking in Mn-Cu alloys manufactured by laser powder bed fusion

Fabricating crack-free Mn-Cu binary alloys via laser powder bed fusion (LPBF) remains challenging due to their high susceptibility to solidification cracking. This study addresses this issue by increasing Cu content. Experimental results indicate that Mn-15Cu and Mn-17Cu alloys exhibit high susceptibility to hot cracking, whereas Mn-20Cu and Mn-25Cu alloys demonstrate a low tendency for cracking. This enhanced cracking resistance is attributed to a narrowed solidification temperature interval, refined cellular substructures, and the formation of continuous Cu-rich boundaries that effectively accommodate thermal stresses. To elucidate the fracture mechanism, a microstructure-based finite-element analysis was performed. The simulations reveal a two-step fracture mechanism in low-Cu alloys: microcracks initiate in the Mn matrix and subsequently propagate through the intervening Cu regions to form through-thickness cracks. Benefiting from the eliminated defects and optimized microstructure (cell size 1.13 μm and grain size 1.3 μm), the as-printed Mn-25Cu alloy achieves a superior combination of strength and ductility, with a yield strength of 530 MPa, ultimate tensile strength of 624 MPa, and elongation of 28.8%.