Pre-precipitating promoted by microshear bands effectively circumvents strength-ductility trade-off of RT-rolled Al–6Zn–1Mg alloy

Abstract

The aging precipitated phases are of great significance for the strengthening and toughening of Al–Zn–Mg alloys. In this work, pre-precipitating was realized through equal channel angular pressing (ECAP) immediately followed by solid solution treatment at 475 °C for 6 h. Its corresponding strengthening and toughening effect on the room temperature (RT)-rolled Al–6Zn–1Mg alloy was systematically studied. The results indicate that pre-precipitating by ECAP can effectively improve the strength of the RT-rolled Al–6Zn–1Mg alloy and circumvent the strength-ductility trade-off. Microstructure characterization reveals that ECAP induces a large number of microshear bands, which can not only encourage recrystallization but also effectively promote the precipitation of the η′ phase. The synergistic effect of precipitation strengthening and dislocation strengthening contributes to the high strength of Al–6Zn–1Mg alloy, with UTS and YS increasing to ∼522 MPa and ∼400 MPa, respectively. Meanwhile, the ductility remains almost unchanged mainly due to the coordinated grain boundary sliding and the uniform and finely dispersed second phase particles. As a result, the strength-ductility trade-off is effectively avoided. The findings shed some light on optimizing the traditional aging treatment.

Keywords

• Al-Zn-Mg alloys
• Equal channel angular pressing (ECAP)
• Precipitation
• Rolling
• Microstructure
• Mechanical property