THERMODYNAMIC ESTIMATION OF STRUCTURAL COMPONENTS OF ALLOY В96Ц
Processy litʹâ, 2019, Tom 136, №4, p.43-51
Keywords:
aluminum alloys, thermodynamics, technological phase diagrams, hot cracks, intermetallicsAbstract
Received 01.07.2019
UDK 669.018.27:536.777
In the article a literary survey of the reasons that significantly affect the formation of hot cracks in high-strength aluminum alloys containing zinc is made. There are various reasons for the formation of hot cracks during casting of high-strength alloys of the Al−Zn−Mg−Cu system, among which one can designate the following: a large crystallization range of alloys, in combination with low temperature solidus; stresses in the cooling interval during crystallization; phases or compounds with a low melting points (eutectics) at the grain boundaries or between the crystals − thin liquid gaps between the grains reduce the strength of the castings; rough grain structure and other reasons. Zinc forms T-phase (Al2Mg3Zn3) during the heat treatment of the high-strength alloys. Excess intermetallic S-phases (Al2CuMg) play a negative role and increase the likelihood of the formation of hot cracks. To obtain qualitative high-strength alloys it is necessary to optimize the chemical composition of all components. To solve this problem we use thermal analysis and thermodynamic calculation method, which is presented in this paper. This technique is based on the use of the software package Thermo-Calc to calculate the solubility of components in the aluminum matrix and the construction of technological phase diagrams. Thus in the article thermodynamic calculations were made and the technological phase diagrams of the alloys system Al−Zn−Mg−Cu with minimum, maximum concentrations of alloying elements and the maximum possible content of impurities were constructed. It has been established that at maximum content of alloying elements S-phase (Al2CuMg) is precipitated along the grain boundaries, which increases the probability of hot cracks formation. With a maximum content of alloying elements, the S-phase is released almost immediately after complete crystallization, just below the solidus line.
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Copyright (c) 2019 В. І. Дубодєлов, А. М. Верховлюк, О. А. Щерецький, Р. А. Сергієнко
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