Influence of Secondary Quasicrystalline I-Phase Precipitates on the Grain Structure and Mechanical Properties of the Al–Mg–Mn Alloy

The parameters of the dispersoids precipitated during low-temperature (at 360°C) and high-temperature (at 450°C) homogenization annealing of the Al–4.9Mg–1.2Mn alloy (Alnovi-U type) ingot have been investigated. The effect of homogenization regime upon the subsequent thermomechanical treatment has been studied on the parameters of grain structure and mechanical properties at room temperature. Low-temperature annealing provided a high number density of I-phase dispersoids with a quasi-crystalline structure and an average size of 35 ± 5 nm. The dispersoids have retained their size and morphology after thermomechanical treatment. Al6Mn-phase dispersoids of a platelate shape with an average longitudinal size of 130 ± 10 nm have precipitated during high-temperature annealing. Precipitation-hardening and dislocation strengthening mechanisms facilitated by I-phase dispersoids during low-temperature annealing of the ingot are responsible for a 40 MPa increase in the yield strength of the alloy as compared to that achieved by conventional high-temperature annealing.