Anastasiya Fortuna

An alloy with a nominal composition of Mn55Al36Ga9 is prepared by four different methods which ensure different cooling rates. Two bulk samples are prepared by induction melting followed by water quenching from a homogenizing temperature of 1100oС; one of the samples was sealed in a quartz ampoule and subjected to water quenching, whereas the other sample directly was subjected to water quenching. Two samples are prepared in the form of ribbons by quenching from the melt on a rotating copper wheel at linear speeds of 10 and 40 m/s. Thus, samples quenched at different rates are prepared. For these samples, regularities of phase transitions occurred during heating are determined, and difference in the regularities for the bulk and rapidly quenched samples are found. Based on the data obtained, we make an assumption that the γ2 → τ phase transition has features of a bulk transition. Magnetic hysteretic properties of the rapidly quenched ribbons are measured. The high thermal stability of the rapidly quenched ribbons alloyed with gallium is shown.

Rapidly quenched Mn55Al36Ga9 ribbons were obtained by the spinning method. In the initial quenched state, the ribbons had a two-phase structure of the ε and γ2-phases. It has been established that, upon heating, the alloy undergoes a series of phase transformations, including the precipitation of the equilibrium β-Mn phase and its subsequent dissolution, the formation of the ferromagnetic τ-phase from both the ε and γ2-phases. The largest amount of the τ-phase was obtained by annealing at a temperature of 700 °C for 20 minutes. The work describes both the phase composition obtained as a result of annealing at different temperatures and the features of the microstructure studied by electron microscopy.

An alloy with a nominal composition of Mn₅₅Al₃₆Ga₉ is prepared by four different methods which ensure different cooling rates. Two bulk samples are prepared by induction melting followed by water quenching from a homogenizing temperature of 1100ºС; one of the samples was sealed in a quartz ampoule and subjected to water quenching, whereas the other sample directly was subjected to water quenching. Two samples are prepared in the form of ribbons by quenching from the melt on a rotating copper wheel at linear speeds of 10 and 40 m/s. Thus, samples quenched at different rates are prepared. For these samples, regularities of phase transitions occurred during heating are determined, and difference in the regularities for the bulk and rapidly quenched samples are found. Based on the data obtained, we make an assumption that the γ₂ → τ phase transition has features of a bulk transition. Magnetic hysteretic properties of the rapidly quenched ribbons are measured. The high thermal stability of the rapidly quenched ribbons alloyed with gallium is shown.

Rapidly quenched Mn₅₅Al₃₆Ga₉ ribbons have been obtained using a spinning method. In the initial quenched state, the ribbon structure is a two-phase one consisting of the ε and γ₂ phases. It has been established that, upon heating, the alloy undergoes a series of phase transformations, including the precipitation of the equilibrium β-Mn phase and its subsequent dissolution, the formation of the ferromagnetic τ phase from both the ε and γ₂ phases. The largest amount of the τ phase was obtained by annealing at a temperature of 700°C for 20 min. This work describes both the phase composition obtained as a result of annealing at different temperatures and the features of the microstructure studied via electron microscopy.

The phase composition, microstructure, and mechanical properties of flat-rolled experimental Al-Cu-Mn system alloy with Si and Zr additions have been studied. The experimental results have been compared with data for the AA2219 commercial alloy pertaining to the same alloying system. Hot deformation of an experimental alloy causes the precipitation of ~100 nm sized dispersoids and refinement of the eutectic phase particles. The yield strength and relative elongation of the hot-deformed experimental alloy are 255 MPa and 8.6%, respectively. Subsequent cold deformation reduces the relative elongation by 3.5% and increases the yield strength by 50 MPa, while the ultimate tensile strength does not change. After long-term 350 °C exposure, the mechanical properties of the experimental alloy remain the same as those of the as-deformed one, whereas the yield strength of the 2219 alloy decreases by 2 times and the ultimate tensile strength by 1.4 times. Comparison of these experimental results with data for the 2219 alloy and other Al-Cu-Mn system alloys cited in this work and reported elsewhere suggests that a good thermal stability of Al-2Cu-2Mn-0.4Si-0.2Zr alloy rolled stock can be achieved through treatment using the regimes designed herein.

This work was focused on studying the possibility of increasing the strength of non-heat-treatable sheet alloy Al2Cu1.5Mn (wt.%) by the joint addition of 1% Mg and 1% Zn. The effect of these elements on the structure and mechanical properties of the new sheet Al2Cu1.5Mn alloy designed for Al₂₀Cu₂Mn₃ dispersoids has been studied by calculations and experimental methods. The obtained data on the phase composition, microstructure, and physical and mechanical properties of the new alloy for different processing routes (including hot rolling, cold rolling, and annealing) have been compared with those for the ternary Mg- and Zn-free alloy. It has been shown that the formation of nanosized Al₂₀Cu₂Mn₃ dispersoids (~7 vol.%) provides for the preservation of the non-recrystallized grain structure after annealing at up to 400 °C (3 h), while Mg and Zn have a positive effect on the strength due to the formation of alloyed aluminum solid solution. As a result, cold-rolled sheets of the Al2Cu1.5Mn1Mg1Zn model alloy showed a substantially higher strength performance after annealing at 400 °C in comparison with the ternary reference alloy. In particular, the UTS is ~360 vs. ~300 MPa, and the YS is 280 vs. 230 MPa. For the example of the Al2Cu1.5Mn1Mg1Zn model alloy, it has been shown that the system is promising for designing new heat-resistant alloys as a sustainable alternative to the 2xxx alloys. The new alloy has an advantage over the commercial alloys (particularly, 2219, 2024, 2014), not only in manufacturability but also in thermal stability. The sheet production cycle for the model alloy is much shorter because the stages of homogenization, solution treatment, and water quenching are excluded.