Controlling the addition of solute Ti in Al-Mg-Zn-Cu-Ni alloy for enhanced high-temperature creep properties

Abstract

This study aims to fundamentally understand the effect of 0.1 at% Ti addition (for introducing solute Ti with low diffusivity into the α-Al matrix) on the microstructure and high-temperature mechanical performance of a heat-resistant Al–5Mg–3.5Zn–2Cu–2Ni (at.%) quinary alloy subjected to heat treatments. The precipitation morphologies of the T-Al6Mg11Zn11 phase are systematically characterized in terms of the distribution of solute Ti, which is controlled by a peritectic reaction during solidification. High-temperature strength and creep properties (200 °C/105 MPa) are examined using the Ti-added alloy specimen and compared with the results of Ti-free quinary alloy specimens. In the Ti-added alloy, solute Ti is distributed within the dendritic α-Al phases formed through the peritectic reaction. The precipitation morphologies vary depending on solute Ti contents in the α-Al matrix after isothermal aging at 200 and 300 °C. Numerous fine T-phase precipitates are homogeneously dispersed in the α-Al matrix containing high solute Ti content. Fine precipitation morphologies appear stable even after long-term exposure at 200 °C. Ti addition extends creep rupture life (at 200 °C) without the loss of static high-temperature strength and room-temperature ductility. The improved creep properties could be responsible for the reduction in creep rate by the refined precipitation morphologies in the α-Al matrix containing higher solute Ti contents. Local coarsening of the precipitates occurs owing to the solute Ti during creep (under stress). The mechanism is discussed in terms of the effect of Ti addition on the phase equilibria between the α-Al and other intermetallic phases.