Microstructural evolution and phase transformation behavior of Al-8.1Zn-2.0Mg-1.0Cu-0.2Ag-0.15Zr alloy during isothermal compression

In this work, the deformation behavior of Al-8.1Zn-2.0Mg-1.0Cu-0.2Ag-0.15Zr alloy was studied under isothermal compression, with strain rate and temperature in the range of 0.001 s⁻¹−10 s⁻¹ and 330 °C−450 °C, respectively. First, it was found that the deformation temperature significantly affected the dynamic recrystallization (DRX) and phase transformation behaviors of this alloy. At 330 °C, discontinuous dynamic recrystallization (DDRX) and arched grain boundaries were observed, whereas dislocation entanglements dominated continuous dynamic recrystallization (CDRX) was notably detected at 370 °C. Temperatures exceeding 410 °C facilitated the CDRX behavior, as polygonal chain-like subgrains and block-like dislocation loops were found within the new grains. High deformation temperatures also resulted in the amalgamation and growth of adjacent subgrains. Moreover, we found the Ag-containing phase spheroidized and grew at high temperatures, while the deformation had little effect on the Al₃Zr. Strain rate also significantly affected the deformation behavior of this alloy. Samples deformed at 0.001 s⁻¹ exhibited prolonged deformation time with clear dynamic recovery (DRV) and DRX. At 1 s⁻¹, irregular dislocation distribution was observed, while at 10 s⁻¹, shear band formation induced by deformation instability was evident. Furthermore, the deformation induced η′/matrix interfacial transformation from Zn clusters to a Zn–Mg common interface. Particularly, the precipitation order at grain boundary was proved to be Zn atomic clusters → Zn, Mg atomic clusters (GP zone) → η′ (MgZn₂).