Influence of Cu/Mg ratio on microstructure and mechanical properties of Al–Zn–Mg–Cu alloys

• Published in: Journal of materials science Vol. 56; no. 4; pp. 3472 - 3487
• Main Authors: Wei, Shilong, Wang, Richu, Zhang, Hui, Xu, Chunting, Wu, Ying, Feng, Yan
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-02-2021; Springer; Springer Nature B.V
• Subjects: Aging (metallurgy); Alloys; Aluminum base alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Copper; Crystallography and Scattering Methods; Degassing of metals; Ductile fracture; Ductile-brittle transition; Grain boundaries; Heat treating; Intergranular fracture; Magnesium; Materials Science; Mechanical properties; Metals; Metals & Corrosion; Microstructure; Morphology; Particle size distribution; Polymer Sciences; Precipitates; Solid Mechanics; Specialty metals industry; Zinc; Zinc compounds
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-020-05438-0

The relationship between microstructure evolution and mechanical performance of Al–Zn–Mg–Cu alloys with varying Cu/Mg ratios was discussed in detail under different two-step aging (T7X). The results showed that the undissolved second-phase particles including
σ
-Al
7
Cu
2
Fe and T-Al
2
Mg
3
Zn occurred in the quenched Al–Zn–Mg–Cu alloys. When the Cu/Mg ratio approaches 1.64, the S-Al
2
CuMg phase was also observed. Although the Cu/Mg ratio did not change the precipitation sequence of the Al–Zn–Mg–Cu alloys, it changed the coarsening rate and precipitate size distribution during aging process. The Al–Zn–Mg–Cu alloy with the lowest Cu/Mg ratio has the slowest coarsening rate and the highest strength (655 MPa). The fracture morphology of Al–Zn–Mg–Cu alloys changes from the typical brittle fracture to the intergranular-dominated mixed fracture mode or ductile fracture when the Cu/Mg ratios increases. Besides, the T79-aged alloys with varying Cu/Mg ratios have similar grain boundary precipitates (GBPs) and precipitate-free zones (PFZs). The T74-aged alloys with higher Cu/Mg ratio have more coarser GBPs and wider PFZs.