Технические науки/1. Металлургия

A.R. Toleuova¹, D.U. Smagulov¹, A.A. Amenova¹

¹- Kazakh National Technical University after K.I. Satbayev, 050013 Almaty, Kazakhstan

On the calculation and representation of multicomponent systems

Introduction

Casting alloys are called, are used for the production of shaped castings. Casting aluminum alloys - widespread (mainly construction) materials consumption is growing every year in almost all sectors of modern industry.

Feature of the production of cast aluminum alloys is the high proportion of recycled materials used. Since only 70 - 85% by weight of the charge for melting of cast aluminum alloys are waste and scrap, which is several times larger than the corresponding figure for deformable aluminum alloys.

Basic requirements for cast aluminum alloys - is a high level of performance (mechanical and corrosion properties) combined with good processability during mlding. Last for the currently used technologies in the industry means lower propensity to hot (crystallization) cracks, good fluidity, minimal shrinkage porosity, ie good casting properties.

In the various branches of technology is now used dozens of cast aluminum alloys. Patented formulations of thousands of alloys. However, almost all of them contain a relatively small number of alloying elements. All the alloying elements that make up the cast aluminum alloys can be divided into three groups: the main alloying elements, small additions and impurities. The same elements can belong to different groups depending on the alloy.

The first and main function of the alloying elements - to increase the strength of aluminum (pure aluminum is too low strength - s_в < to 60 MPa). Hardening is achieved by formation of solid solution, and - in many systems - through precipitation hardening. In addition, the content of alloying elements depends on the properties of casting alloys, which largely determines their technology and, consequently, the degree of industrial use.

Figure 1. Isothermal section of Al-Cu-Mn-Zr - Fe - Si at 0,3% Fe, 0,4% Zr at 540 °C.

The experimental part

Obviously, to make informed choices concentrations of impurities, alloying elements and heat treatment, a careful analysis of Al-2Cu-1, 5Mn-0, 4Zr - 0,1 ÷ 0,3 Fe - 0,1 ÷ 0,3 Si. Therefore, in this paper has been tasked to perform such an analysis using modern software Thermo - Calc. This program allows you not only to build almost any size, but to count on a quantitative level the phase composition of the alloy at different temperatures (including the mass and volume fractions of phases and the concentration of these elements). No calculation to get this information is practically impossible.

The addition of zirconium binary alloys have been known to lead to the formation phase Al₃Zr. Although the literature there are no data on the structure of the diagram Al-Cu-Mn-Zr-Fe-Si, distribution of phase domains in the aluminum corner of the system in the solid state can be predicted based on available information. It is known that zirconium greatly increases the liquidus temperature in binary alloys. It is also known that adding zirconium improves the resistance of various types of corrosion. At the same time be sure to take into account that the positive effect of zirconium can be achieved only in strict compliance with technology. Otherwise, its presence in the alloy may be useless and even harmful. For example, if the temperature of the melt with this addition, the input, usually from the ligature, was too low, then the structure might have a rough castings of primary aluminides, which reduce the mechanical properties.

Figure 2. Isothermal section of Al-Cu-Mn-Zr - Fe - Si at 1,5% Mn, 0,3% Si at 540 °C.

In the non-equilibrium solidification conditions the solubility of manganese in aluminum increases, and the formation of a ternary compound is suppressed. Therefore, in these alloys, together with (Al) phase coexist Al₂Cu and Al₆Mn. After the formation of primary crystals (Al), there is an evolution of phases and Al₂Cu Al₂₀Cu₂Mn₃ by the following reaction: L ® (Al) + Al₂Cu + Al₂₀Cu₂Mn₃ at 547 ° C. With further increase of the concentration of copper significant changes were observed.

Aluminum angle of the phase diagram characterized by a rather complex structure. In equilibrium with the aluminum solid solution phases, except for the binary systems (Al₆Mn and (Si)) is a ternary compound α_m (Al₁₅Mn₃Si₂). In the non-equilibrium solidification conditions in aluminum alloys can also be present phase Al₄Mn and Al₁₀Mn₃Si.

Figure 3. Isothermal section of Al-Cu-Mn-Zr - Fe - Si at 0,3% Fe, 1,5% Mn at 540 °C.

Below is a nonvariant reaction that may occur in the system Al-Cu-Mn-Zr - Fe - Si: L ® b(Al) + Si + α_m at 0,3% Fe, 0,2% Mn and ~ 575 ° C.

Phase Al₁₅Mn₃Si₂ (26,3% Mn, 8,9% Si), denoted as and Al₁₀Mn₂Si, Al₁₂Mn₃Si, Al₉Mn₂Si_{1, 8}, α (MnSi) or α_m, there is a homogeneity range 25 - 29% Mn, 8 - 13 % Si. Phase α_m is skeletal form and has a less harmful effect on the mechanical properties of the alloy as compared to other phases. Primary crystals of this phase have the form of equiaxed polyhedra, they often form clusters. This phase has a cubic lattice (space group Pm3, 138 atoms per unit cell) with a = 1.265 - 1.260 nm . The density of 3.55 g/cm³ phase, while the microhardness at room temperature, 8.8 GPa. Silicon is slightly soluble in phase Al₆Mn. The solubility of manganese in the phase Al₁₅Mn₃Si₂ is 0.7 - 0.8%.

Table 1.

The parameters characteristic of the crystallization of alloys of the Al-Cu-Mn-Zr - Fe – Si

Fe, %	Si, %	Cu, %	tL, °C	tS, °C	Phases
0,1	0,1	0,5	790	639	(Al) +Al6Mn +Al3Zr
0,3	0,3	5	788	557	(Al) +Al20 +Al3Zr + αm

Liquidus temperature (T_L) and solidus (T_S) is one of the most important characteristics of any alloy. With these temperatures determine the modes of heat treatment temperature of melting and casting alloys. The results of calculating the values of T_L and T_S for the alloy of Al - Cu - Mn - Zr-Fe - Si are shown in Table. 1. Based on the calculation results we can conclude that copper does not affect the T_L, but significantly reduces the T_S. On the other hand, iron and silicon in small quantities do not significantly affect the liquidus and solidus.

Conclusions. Using the program Thermo-Calc quantitative analysis of the phase diagram of Al - Cu - Mn - Zr - Fe - Si (isothermal sections, temperature, solidus and liquidus).

The composition of this alloy has a very narrow limits. Copper is added to reduce the pitting corrosion. Allowed up to 0.5% iron and silicon, which leads to some strengthening of the alloy, without significant loss of corrosion resistance. Under equilibrium conditions present in the alloy phase Al₁₅Mn₃Si₂, which does not exert a strong influence on the mechanical properties of the alloy.

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