Unravelling crack tip damage mechanisms: In-situ tensile assessment of Al-6Zn-2.1 Mg-2Cu alloy strengthened by Ti, Zr, and Sc micro-alloying

• Published in: Engineering fracture mechanics 2024-12, Vol.312, p.110663, Article 110663
• Main Authors: Mukherjee, Diya, Tiwari, Yoshit, E, Chandrasekar, Mandal, Nilrudra, Qiu, Dong, Mukherjee, Manidipto, Easton, Mark A., Roy, Himadri
• Format: Article
• Language: English
• Subjects: Aluminium alloys; Crack tip damage mechanism; In-situ SEM tensile testing; Scandium; Small scale specimen testing
• ISSN: 0013-7944
• DOI: 10.1016/j.engfracmech.2024.110663

[Display omitted] •In-situ FESEM tensile testing reveals crack tip deformation in microalloyed Al-6Zn-2.1 Mg-2Cu alloys.•Ti, Zr, and Sc additions refine α-Al cell size from 48 µm to 30 µm via intermetallic dispersoids.•Quasi-brittle fracture occurs via cleavage and intermetallic decohesion.•Optimal microalloying enhances crack resistance, but excess causes coarse dispersoids and early fracture.•Void nucleation occurs around coarse S-Al2CuMg and η-MgZn2 particles at grain boundaries. This study investigates the effect of micro-alloying elements (Ti, Zr and Sc) on the crack tip damage behaviour of cast Al-6Zn-2.1Mg-2Cu-X alloys to understand the effect of grain boundary interfaces, matrix, intermetallics and dispersoids on deformation and fracture behaviour. Notched tensile specimens were prepared and subjected to in-situ tensile deformation under FESEM to investigate the crack initiation, propagation, and eventual failure processes under uniaxial tensile loading. The experimental results reveal that fracture in the four Al-6Zn-2.1Mg-2Cu-X alloys is quasi-brittle due to strain accumulation and cleavage fracture mechanisms. The crack mainly initiates from the grain boundary lath S-Al2CuMg and η-MgZn2 intermetallic phases. Adding 0.25 % Sc forms small coherent Al3(Sc, Zr) dispersoids, increasing crack resistance. The ductility of the matrix is due to void nucleation, crack meandering, and crack tip-blunting phenomena. At high additions of microalloying elements (1 wt%), large Al3(Zr, Ti) intermetallics form and agglomerate, contributing to premature fracture. These findings from materials characterization and in-situ tensile testing indicate potential methods to enhance the fracture toughness of Al-6Zn-2.1Mg-2Cu alloys with additions of Zr, Ti, and Sc.