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Oxide dispersion strengthened (ODS) alloys with a high content of Al are candidate materials for extreme high temperature applications such as turbine blades and other components working at temperatures significantly above 1000 °C. While oxidation kinetics of Fe–Al ODS steels is frequently studied, the stability and growth kinetics of strengthening oxide dispersion is a rarely studied topic. The Fe-10Al-4Cr-4Y2O3 is an experimental material, fabricated at IPM by powder metallurgy route and contains much higher volume fraction of Y2O3 than similar materials. Stability and growth kinetics of Y2O3 particles of our material are studied on 24 samples aged for 0.5, 1, 2, 4, 8, 16, 32 and 72 h at 1200 °C, 1300 °C and 1400 °C. The sizes of at least 600 individual Y2O3 particles are measured on each sample to obtain extensive statistical analysis of the particle growth. The average particle size coarsens from 28.6 ± 0.7 nm to 36.9 ± 0.9 nm in 1200 °C series and to 81.4 ± 5.6 nm in 1400 °C series. The evaluated activation energy of coarsening of Y2O3 particles is 274 ± 65 kJ. The effects of particle coarsening on mechanical properties is demonstrated by HV measurements, which is in very good agreement with the Orowan theory.

Thermo-mechanical fatigue (TMF) is one of the most detrimental failures of critical engine components and greatly limits their service life. In this study, the out-of-phase TMF (OP-TMF) behavior in Al-Si-Cu 319 cast alloys microalloyed with Mo was systematically investigated under various strain amplitudes ranging from 0.1–0.6% and temperature cycling at 60–300 °C and compared with the base 319 alloy free of Mo. Cyclic stress softening occurred in both experimental alloys when applying the TMF loading, resulting from the coarsening of θ’-Al2Cu precipitates. However, the softening rate of the Mo-containing alloy was lower than that of the base 319 alloy because of its lower θ’-Al2Cu precipitate coarsening rate per cycle. The Mo-containing alloy exhibited a longer TMF lifetime than the base alloy at the same strain amplitude. Microalloying 319 alloy with Mo enhanced the TMF resistance mainly by slowing the coarsening of θ’-Al2Cu precipitates and providing supplementary strengthening from thermally stable Mo-containing α-dispersoids distributed in the Al matrix. The energy-based model was successfully applied for predicting the TMF lifetime with a low life predictor factor, which agreed well with the experimentally measured fatigue cycles.

In the present work, we investigated the possibility of introducing fine and densely distributed α-Al(MnFe)Si dispersoids into the microstructure of extruded Al-Mg-Si-Mn AA6082 alloys containing 0.5 and 1 wt % Mn through tailoring the processing route as well as their effects on room- and elevated-temperature strength and creep resistance. The results show that the fine dispersoids formed during low-temperature homogenization experienced less coarsening when subsequently extruded at 350 °C than when subjected to a more typical high-temperature extrusion at 500 °C. After aging, a significant strengthening effect was produced by β″ precipitates in all conditions studied. Fine dispersoids offered complimentary strengthening, further enhancing the room-temperature compressive yield strength by up to 72–77 MPa (≈28%) relative to the alloy with coarse dispersoids. During thermal exposure at 300 °C for 100 h, β″ precipitates transformed into undesirable β-Mg2Si, while thermally stable dispersoids provided the predominant elevated-temperature strengthening effect. Compared to the base case with coarse dispersoids, fine and densely distributed dispersoids with the new processing route more than doubled the yield strength at 300 °C. In addition, finer dispersoids obtained by extrusion at 350 °C improved the yield strength at 300 °C by 17% compared to that at 500 °C. The creep resistance at 300 °C was greatly improved by an order of magnitude from the coarse dispersoid condition to one containing fine and densely distributed dispersoids, highlighting the high efficacy of the new processing route in enhancing the elevated-temperature properties of extruded Al-Mg-Si-Mn alloys.

The present work has systematically investigated the evolution of dispersoids and elevated-temperature properties including strength and creep resistance during various multi-step heat treatments in Al-Mn-Mg 3004 alloys. Results show that only the α-Al(MnFe)Si dispersoid is observed in the studied temperature range (up to 625 °C), and that it coarsens with increasing temperature to 500 °C, but dissolves at 625 °C. The evolution of elevated-temperature strength and creep resistance is greatly related to the temperature of each step during the multi-step heat treatments. Generally, lower temperature at the first-step heat treatment leads to higher properties, while the properties decrease with increasing temperature of last-step heat treatment. Suitable models have been introduced to explain the evolution of strength and the creep threshold stress at elevated-temperatures during the various heat treatments.

In the present work, the hot rolling at 400°C and post-rolling annealing at 500°C were applied on heat-treated Al-Mg-Si 6082 alloys with different Mn contents to study the evolution of microstructure and elevated-temperature properties. During the pre-heat treatment before rolling (400°C/2h), a number of fine rod-like dispersoids formed in Mn-containing alloy while only high volume of larger Mg 2 Si particles was observed in the matrix of base alloy free of Mn. After hot rolling, the morphology of dispersoids was transferred from rod-like to spherical with finer size and increased number density while the dispersoids gradually coarsened during post-rolling annealing in Mn-containing alloy. The full recrystallization was completed after 1-2 h during annealing in the base alloy, while only partial recrystallization was observed in Mn-containing alloy. The micro-hardness at room temperature and the tensile yield strength at 300°C firstly increased from as-rolled condition to the initial stage of annealing (1 h) for both alloys, which was likely attributed to the dissolution of Mg 2 Si during the beginning of annealing. With further increasing annealing time (2-8 h), both the microhardness at room temperature and the elevated-temperature strengths of the base alloy remained similar, while they were slightly decreased in Mn-containing alloy owing to the partially recrystallization and coarsening of dispersoids. However, the elevated-temperature strengths were always higher in Mn-containing alloy than the base alloy while their differences between two alloys was reducing with prolonging the post-rolling annealing time. The tensile fracture surface was observed to be ductile for all the conditions of both alloys but the dimples in Mn-containing alloy were finer and much more uniformly distributed.

Al-8·5Fe-1·3V-1·7Si (wt-%) alloy consolidated and rolled into sheet from pulverised planar flow cast material has been subjected to exposure times up to 575 h at 625°C. Both as received and exposed samples were investigated to reveal the effect of the exposure on microstructural stability, including dispersoid size. Microstructural characterisation was performed by a combination of X-ray diffraction, differential thermal analysis, and scanning and transmission electron microscopy. The results showed the presence of coarse plate shaped Al 13 Fe 4 particles after 2 h at 625°C and additional polyhedral shaped Al 13 (Fe,V) 3 Si particles were observed evenly distributed within the matrix after exposure at 625°C for 290 h. Even after 575 h at 625°C, the silicide phase in the material retained the same bcc structure as in the as received condition but with a slightly increased lattice parameter. The experimentally determined coarsening rates of silicides in the material were a factor of 2 to 3 lower than predictions based on control by volume diffusion of V in the α-Al matrix.