Hereditary Effect of the Structure of the Charge on Density, Gas Content, and Processes of Solidification of an Al–Si–Cu Alloy System

• Published in: Russian journal of non-ferrous metals Vol. 61; no. 3; pp. 265 - 270
• Main Authors: Nikitin, K. V., Nikitin, V. I., Timoshkin, I. Yu
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.05.2020; Springer Nature B.V
• Subjects: Alloy systems; Alloys; Aluminum base alloys; Anomalies; Backfill; Cast iron; Charge density; Chemistry and Materials Science; Cold molding; Cooling rate; Copper; Crystallization; Eutectic temperature; Foundry; Heredity; Ingot casting; Liquid-solid systems; Liquidus; Low temperature; Materials Science; Metallic Materials; Parabolic bodies; Phase transitions; Process parameters; Silicon; Solidification; Solids; Temperature; Temperature dependence; Thermal analysis; phase-transition temperatures during solidification; silumins; density in liquid and solid states; charge billet; modification; structure; structural heredity
• ISSN: 1067-8212; 1934-970X
• DOI: 10.3103/S1067821220030104

The effect of the structure of the initial charge density in liquid and solid states, as well as on the temperature–time parameters of the process of solidification of the AK6M2 alloy (Al–6% Si–2% Cu), is shown. To obtain a coarse-crystal charge (C charge), part of the melt is crystallized in ceramic forms in a sand backfill with a cooling rate of ~0.5–1.0°C/s. The fine-crystal charge (F charge) in the form of thin ingots weighing 0.2–0.3 kg is obtained by crystallization of the melt in cast-iron cold molds with ~5.0–10°C/s. Further, the charge billets are separately melted, re-refined and degassed, and the samples are poured to determine the gas content and density in the liquid ( d L ) and solid ( d S ) states. It is established that structural information from the original charge of the alloy is stable in the solid–liquid–solid system. Direct thermal analysis is used to find that the melt obtained from the F charge hardens at low temperatures: the decrease in liquidus temperature t L is 3°C; the temperature of the beginning of solidification of the eutectic is reduced by 10°C, and the temperature of the end of solidification of a eutectic is 3°C in comparison with the melt of the C charge. At the same time, the formation of α-Al and eutectic dendrites in the melt from the F charge occurs 0.4 and 0.6 min more quickly, respectively. The results obtained on the Paraboloid-4 installation show that a smaller number of pulses throughout the studied temperature range passes through the melt from the F charge, which confirms its increased density when compared to the alloy from the C charge. Thus, for the melt from the F charge, the values of the degrees of compaction were –Δ J l ~ 278.66 and –Δ J e ~ 129.83 imp/s and, for the melt from the C charge, –Δ J l ~ 302.9 and –Δ J e ~ 163.47 imp/s. The values of the phase-transition temperatures determined by anomalies on the temperature dependence Jt practically coincide with the results of direct thermal analysis. The main technological recommendations of management by structural information in aluminum alloys are formulated from the position of the phenomenon of structural heredity.