Improving element uniformity and mechanical properties of Al-Mg-Si alloy fabricated by twin roll casting with superheat melt treatment

The effect of superheat melt treatment(SMT) on microstructure and properties of Al-Mg-Si alloy fabricated by twin roll casting(TRC) was analyzed using optical microscope, scanning electron microscopy, emission electron probe micro analyzer and transmission electron microscopy. SMT increased the subcooling degree of melt during TRC. The solidification microstructure with high dendrite density and small dendrite spacing was obtained. The second phase was evenly distributed between dendrites and the solute concentration gradient was decreased. Intergranular solute aggregation caused by Reynolds’ dilatancy in TRC slab was effectively suppressed. The homogeneous solute distribution of TRC slab with SMT can be realized by short-time homogenization heat treatment. The size of insoluble particles was greatly reduced. The complete decomposition of non-equilibrium eutectic phase increased the solute concentration in α-Al, which promoted the precipitation of precipitates during aging heat treatment. The tensile strength and yield strength of T6 slab were improved, while the uniform elongation are almost not decreased. The strength and uniform of slab in T4P state were both improved. The obtained results can help further shorten the production cycle of TRC slabs and improve mechanical properties.

Rheological characteristics of steel in continuous roll casting-rolling

Problems. In the process of obtaining a strip in a casting and rolling device, the question arises of combining the process of hot rolling of the solidified material and the process of crystallization of the liquid melt. This makes it possible to implement an efficient technology for producing thin-sheet products. Purpose of the study. Determination of rational parameters for performing mathematical modeling of material behavior during roll casting requires clearly defined recommendations. The material for the rolling process is steel. The starting material was used in solid, solid-liquid and liquid states. Implementation technique. The analysis of the properties of steel was carried out on the basis of the results of experiments obtained at the Physico-Technological Institute of Metals and Alloys of the National Academy of Sciences of Ukraine. To analyze the rheological properties of steel, the dependences of the yield stress for alloyed and carbon steels were used in a certain temperature range. The selected temperature range includes solidus and solid-liquid state of steel, located above 0.8 melting point. Research results. Based on the research results, the analysis of the rheological properties of steel in solid, solid-liquid and liquid states during continuous casting-rolling on rolls was carried out. The use of the obtained dependencies makes it possible to perform mathematical modeling of the deformation and hydrodynamics of the material during continuous casting-rolling of steel strips using roll casting-rolling devices. Conclusions. The constructed dependences, together with studies of the viscosity of steel in the liquid state and the resistance of steel to deformation in the solid state, most fully describe the rheological properties of steels during casting-deformation processes. The obtained dependences will make it possible to implement an ultra-efficient technology for producing thin-sheet rolled products.

Microstructure and Hot Workability of Twin-roll Cast Dispersoid-strengthened Al- Mg-Si-Mn alloys

Dispersoid-strengthened Al-Mg-Si-Mn aluminum alloys were produced by twin-roll casting (TRC) and conventional mold casting (MC). An extra-low temperature homogenization was performed at temperature of 430 °C for 6 h, which was followed by uniaxial hot compression tests. The results showed that the as-cast TRC samples had a lower eutectic fraction with a smaller size and a higher solid solution concentration compared to the as-cast MC samples. During the extra-low temperature homogenization, a large number of α-Al(Fe, Mn)Si dispersoids precipitated, and the dispersoids in the TRC sample had a greater number density than those in the MC sample. Precipitation-free zone (PFZ) formed near the eutectic regions, TRC sample had a lower PFZ fraction than that of MC sample. The TRC samples yielded higher flow stresses of hot deformation than MC sample owing to the stronger dispersoid strengthening effect. Severe edge cracking occurred in the deformed MC samples due to the high fraction of coarse AlFeMnSi intermetallic particles, no edge crack formed in the TRC samples owing to its lower fraction and fine intermetallics which improved the hot workability of TRC sample.

MODELING OF ROLL CASTING AND ROLLING OF METALS

В данной работе представлены результаты изучения процесса валковой разливки с применением методов физического и математического моделирования. Показано, что стабильность процесса валковой разливки-прокатки металлов зависит от таких технологических параметров, как температура перегрева, скорость разливки и уровень расплава в межвалковом пространстве. Для использованных в процессе исследования сплавов получены зависимости оптимальной скорости разливки-прокатки от толщины полосы, угла мениска металла, радиуса валков и температуры перегрева расплавов.Экспериментальная составляющая данных исследований, выполненная в лабораторных условиях на установке валковой разливки металлов, подтвердила адекватность и высокое качество расчетных режимов разливки для всех изучаемых сплавов. Полученная для описания изучаемых процессов валковой разливки металлов математическая модель показала высокую корреляцию теоретических и экспериментальных данных, что свидетельствует о корректности данной модели. This paper presents the results of studying the roll casting process using physical and mathematical modeling methods. It is shown that the stability of the roll casting-rolling process of metals is provided by such technological parameters as the overheating temperature, the casting speed and the melt level in the inter-roll space. For the alloys used in the study, the dependences of the optimal casting-rolling speed on such technological indicators as the thickness of the strip, the angle of the metal meniscus, the radius of the rolls and the temperature of overheating of the melts were obtained. The experimental component of these studies, performed under laboratory conditions at the roll casting plant of metals, confirmed the adequacy and high quality of the calculated casting modes for all the studied alloys. The mathematical model obtained to describe the studied processes of roll casting of metals showed a high correlation of theoretical and experimental data.

Fluidity Investigation of Pure Al and Al-Si Alloys

Fluidity tests of pure aluminum 1070 and Al-Si alloys with Si contents of up to 25% were conducted using a die cast machine equipped with a spiral die. The effects of the channel gap, die temperature, and injection speed on the fluidity were investigated. When the channel gap was small (0.5 mm), the flow length of the 1070 was minimized, and the fluidity increased monotonically at a gradual rate with increasing Si content. In contrast, larger gaps yielded convex fluidity–Si content curves. Additionally, heating the die had less of an influence on the fluidity of the 1070 than on that of the Al-Si alloy. These results are discussed in the context of the peeling of the solidification layer from the die based on the thicknesses of foils and strips cast by melt spinning and roll casting, respectively. At lower Si contents, heat shrinkage was greater and the latent heat was lower. When the heat shrinkage was greater, the solidification layer began to peel earlier, and the heat transfer between the solidification layer and the die became smaller. As a result, the fluidity of the 1070 was greatest when the channel gap was 0.8 mm.