Effect of vanadium on the microstructures and mechanical properties of an Al–Mg–Si–Cu–Cr–Ti alloy of 6XXX series

Abstract

Vanadium can be considered as a minor element to improve mechanical properties of wrought aluminium alloys by modifying their microstructures. However, so far, it is not widely used in wrought aluminium alloys due to its indissolubility during smelting and solidification. In the present work, Al–4wt.% V master alloys were prepared with different solidification rates and these master alloys were introduced to a commercial Al–1.6Mg–1.2Si–1.1Cu–0.16Cr–0.03Ti (all in wt.%) wrought alloy to study the effect of vanadium on the microstructures and mechanical properties of this alloy. The results showed that the fast solidification rate resulted in the formation of petal-like shaped Al3V phase in Al–4wt.% V master alloy, while the slow solidification rate resulted in the formation of Al10V phase with coarse plate shape. The addition of Al3V phases into the experimental alloy not only promotes the formation of a fine, equiaxed as-cast grain structure, but also inhibits the recrystallisation nucleation and grain growth during hot extrusion and subsequent T6 heat treatment. In this case, the main vanadium phase in this alloy is the metastable and fine Al(VCrTi)Si phase with elliptical morphology and relatively high vanadium content. And the Al(VCrTi)Si phases developed from Al3V phases could pin the movement of dislocations and impede recrystallisation nucleation and growth, resulting in the improvement of mechanical properties. In the experimental alloy with the addition of Al10V phases, the stable AlVMg phase and Al10V phase with angular shape are observed, which does not show the significant inhibiting effect on recrystallisation, resulting in no improvement of ultimate tensile strength and plasticity. In brief, the introduction of Al–V master alloy into the experimental alloy can improve the mechanical properties, however it strongly depends on the type and shape of phases in the Al–4wt.% V master alloy.