Influence of V additions on microstructures, tensile and fatigue properties of Al–Zn–Mg alloys

Abstract V addition with range from 0–0.09 wt% are added in extruded Al–Zn–Mg alloys to study the influence of V addition induced microstructures on the tensile strength and fatigue properties of Al–Zn–Mg alloys under T74 temper. The V addition significantly inhibits the recrystallization behavior of the alloy via forming Al23V4 second phase particles, and the formation of coarse grain layer on the profile surface is gradually inhibited. The aging hardening curve, tensile strength, and fatigue strength of Al–Zn–Mg alloy with different V content are studied. It is discovered that an increase of V content obviously improves the tensile properties and the median fatigue strength of the investigated alloy, but has little effect on the aging hardening rate of the investigated alloys. In fact, the alloy with 0.09 wt% V content has the highest tensile properties, and its tensile strength and yield strength are 374.4 and 329.0 MPa, respectively. The alloy with 0.05 wt% V content achieves the maximum median fatigue strength, which is 183.6 MPa. After T74 aging treatment, the main strengthening mechanism is Orowan bypass strengthening mechanism. However, the excessive V addition has limited effect on the strength improvement of the studied alloys, and has adverse effects on tensile toughness and fatigue strength, mainly because the V atoms will agglomerate in the aluminum matrix and form micron-sized coarse V-rich particles, with an average particle size of about 10 μm.