Aluminium Alloy Phase Diagrams

Aluminium-rich solid solutions are often formed and are referred to as ct-phase, ctAi-phase, or a-Al solid solution. Most of the phases occurring in equilibrium with ct-Al are hard. They consist of elements or intermetal-lic compounds such as AI2CU, AlgMgs, AlgMn, AlgEe, and AlLi. 

Aluminium-Copper. Al-Cu forms a simple eutectic system in the range from 0 to 53wt% Cu, as shown in Fig. 3.1-11. The a-Al solid solution and the intermetaUic compound AI2CU (9 phase) are in equilibrium At intermediate temperatures, metastable transition phases may form and precipitate from the supersaturated solid solution. These metastable phases may be characterised according to their crystal structure, the nature of the phase boundary they form, and their size  

The properties of aluminium strongly depend on the concentration of alloying additions and impurities. Even the low residual contents of Fe and Si in unalloyed aluminium (A199 to A199.9) have a marked effect. 

The main alloying elements of Al materials are Cu, Si, Mg, and Zn while Mn, Fe, Cr, and Ti are frequently present in small quantities, either as impurities or additives. Ni, Co, Ag, Li, Sn, Pb, and Bi are added to produce special alloys. Be, B, Na, Sr, and Sb may be added as important trace elements. All of these elements affect the structure and thus the properties of an alloy. The compositions of the more important aluminium materials are discussed below, using the relevant phase diagram. All alloying components are completely soluble in liquid aluminium if the temperature is sufficiently high. However, these elements have only limited solubility in solid solution. Continuous solid solubil- 

These phase transformations are decisive for the precipitation-hardening behavior of Al-Cu-based technical A1 alloys. 

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Wri] Wriedt, H.A., The Al-N (Aluminium-Nitrogen) System , Bull. Alloy Phase Diagrams, 7, 329-333 (1986) (Phase Diagram, Phase Relations, Review,, 54)... 

Rag] Raghavan, V., The Al-Fe-P System (Aluminium-Iron-Phosphorus) , J. Alloy Phase Diagrams, 5(1), 32-39 (1989) (Review, Crys. Structure, Phase Diagram, Phase Relations, 5)... 

Of the generic aluminium alloys (see Chapter 1, Table 1.4), the 5000 series derives most of its strength from solution hardening. The Al-Mg phase diagram (Fig. 10.1) shows why at room temperature aluminium can dissolve up to 1.8 wt% magnesium at equilibrium. In practice, Al-Mg alloys can contain as much as 5.5 wt% Mg in solid solution at room temperature - a supersaturation of 5.5 - 1.8 = 3.7 wt%. In order to get this supersaturation the alloy is given the following schedule of heat treatments. 

When the phase diagram for an alloy has the shape shown in Fig. 10.3 (a solid solubility that decreases markedly as the temperature falls), then the potential for age (or precipitation) hardening exists. The classic example is the Duralumins, or 2000 series aluminium alloys, which contain about 4% copper. 

The aluminium casting alloys are mostly based on the Al-Si system (phase diagram Fig. A1.31). It is a classic eutectic system, with a eutectic point at about 11% Si and... 

G. Ghosh, Aluminium-chromium—copper, in Ternary Alloys A Comprehensive Compendium of Evaluated Constitutional Data and Phase Diagrams, G. Petzow and G. Effenberg, Ed., VCH Publishers, New York, 1992, pp. 311-319. 

Aluminium alloys form one of the most widely used groups of materials in existence. They make products which are often cheap and can be applied to many different areas. Extensive work has been done on the experimental determination of binary and ternary phase diagrams, mainly during the mid-part of this century, and researchers such as Phillips (1961) and Mondolfo (1976) have produced detailed reviews of the literature which provide industry standard publications. However, although some important Al-alloys are based on ternary systems, such as the LM2S/ 356 casting alloy based on Al-Mg-Si, in practice they inevitably include small amounts of Cu, Mn, Fe, Ti etc., all of which can significantly modify the castability and properties of the final product. The situation is further exacerbated by the use of scrap material. It is therefore useful to be able to predict phase equilibria in multi-component alloys. 

According to the ternary phase diagrams of aluminium-chromium-nickel [7] chromium is soluble in p-NiAl up to about 4 at.% at 1000°C. This is in agreement with the EPMA results for these alloys.The 0 at 1 at.% Cr alloys were homogeneous whereas, segregation was observed in the 5 and 10 at.% Cr alloys. In Table 2 the composition of the alloys, determined with XRF, is reported. In the EPMA-micrographs in Fig. 3 chromium enrichment (a-Cr) can be seen at the grain boundaries. 

Soe] Soehnehen, V.E., Piwowarsky, E., About the Influence of Alloying Elements Nickel, Silicon, Aluminium and Phosphorus on the Carbon Solubility in Liquid and Solid Iron (in German), Arch. Eisenhuettenwes., 5(2), 111-121 (1931) (Experimental, Morphology, Phase Diagram, 51)... 

Mor] Morral, F.R., The Constitution of Iron-Rich Iron-Aluminium-Carbon Alloys , J. Iron Steel Inst., London, 130, 419-428 (1934) (Phase Diagram, Experimental,, , 45)... 

Gorl] Gorev, K.V., Gurinovieh, V.I., The Diagram of State of Fe-Al-C Alloys with a Low Content of Aluminium , Vest. Akad. Navuk BSSR (Fiz.-Tekh.) Navuk, (4), 26—30 (1980) (Phase Relations, Phase Diagram, ExperimentaL 7)... 

Rag] Raghavan, V., The Al-C-Fe (Aluminium-Carbon-Iron) System in Phase Diagrams of Ternary Iron Alloys. Parti", ASM International, Metals Park, OH, 89-97 (1987) (Phase Relations, Phase Diagram, Review, 30)... 

Kor2] Kornilov, I.I., New Heat-Resistant Fe-Cr-Al Alloys wifli High Electrical Resistance (in Russian), Izv. Akad. NaukSSSR, Ser. Khim., (5), 751-757 (1940) (Experimental, 15) [1943Mon] Mondolfo, L.F., Al-Cr-Fe , in Metallography of Aluminium Alloys , John Wiley Sons Inc., New York, 70-71 (1943) (Phase Diagram, Review,, , 1)... 

Phi] Phillips, H.W.L., Al-Cr-Fe , in Equilibrium Diagrams of Aluminium Alloy Systems. Information Bulletin 25 , Aluminium Development Association, London, 1-78 (1961) (Phase Diagram, Review, 1)... 

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