Effect of minor Sc and Zr on recrystallization behavior and mechanical properties of novel Al–Zn–Mg–Cu alloys

• The samples were subject to different annealing and aging treatments.
• The microstructure of the alloys was analyzed with EBSD technique.
• Al-0.6(Sc + Zr) alloy exhibited the best mechanical properties.
• The subgrain strengthening and precipitate strengthening dominated strength.

Effect of trace amount of Sc and Zr on microstructure and mechanical properties of novel Al–Zn–Mg–Cu–Sc–Zr alloys are investigated. The samples were subjected to different annealing temperatures and various aging times. Analysis of microstructure and mechanical properties were carried out on TEM, EBSD technique, Vickers hardness test and tensile test. The results showed that abundant nanometer-sized Al3(Sc, Zr) particles effectively pined dislocations and subgrain boundaries, exhibiting excellent antirecrystallization behavior and precipitates strengthening effect. Al–Zn–Mg–Cu alloys exhibited completely recrystallized structure after annealing at 470 °C for 1 h. However, the two Al–Zn–Mg–Cu–Sc–Zr alloys exhibited equiaxed grains at 600 °C. Besides, with the additions of Sc and Zr increased, a higher density of precipitates was detected obviously with excellent refinement effect. After solution-aging treatment, the maximum values of hardness, tensile strength and yield strength were 240 HV, 668 MPa, 628 MPa respectively, which were obtained by Al–Zn–Mg–Cu–0.22Sc–0.40Zr alloy at 120 °C for 24 h. The grain refinement strengthening and precipitation strengthening play a dominant role in the additional strength of the Al–Zn–Mg–Cu–Sc–Zr alloys.

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