A review of the experimental and computed data on this ternary system was reported recently by [2007Rag] and [2006Pet]. The (Mg)-solvus in Mg-rich alloys was recently determined by [2009Ren] at 320 °C.

Binary Systems

The Al-Mg phase diagram has the following intermediate phases: Mg2Al3 (denoted β; cubic, space group \(Fd\bar{3}m\)), R or ɛ (rhombohedral) and Mg17Al12 (denoted γ; α-Mn type cubic). The Al-Zn phase diagram [Massalski2] contains no intermediate phases. A miscibility gap occurs in the Al-based face centered cubic (fcc) solid solution below 351 °C, where the fcc phase splits into (Al)′ and (Al)′′. The monotectoid reaction (Al)′′ ↔ (Al)′ + (Zn) follows at 277 °C. The Mg-Zn phase diagram [Massalski2] depicts the following intermediate phases: Mg7Zn3 (high-temperature phase), MgZn, Mg2Zn3 (monoclinic), MgZn2 (C14-type hexagonal) and Mg2Zn11 (D8 c -type cubic).

Ternary Phases

Two ternary phases are known in this system. (Al,Zn)49Mg32 (denoted τ) is cubic, space group \(Im\bar{3}\). Al2Mg5Zn2 (denoted ϕ) is orthorhombic and has a range of homogeneity.

Isothermal Section at 320 °C

With starting metals of 99.99% Al, 99.99% Mg and 99.999% Zn, [2009Ren] induction-melted under Ar atm 14 Mg-rich ternary alloys containing up to 33 at.% Al and 40 at.% Zn. The alloys were annealed at 320 °C for 720 h and quenched in water. The phase equilibria were studied with x-ray powder diffraction and scanning electron microscope equipped with energy dispersive x-ray analyzer. The identified phases and their compositions were listed. The partial isothermal section constructed by [2009Ren] at 320 °C is shown in Fig. 1. Figure 2 shows the details at the Mg corner. (Mg) is in equilibrium with both τ and ϕ phases. The homogeneity range of ϕ was found to be 14.7-27 at.% Al and 30.5-17.7 at.% Zn, agreeing with the result of [1997Don] at 335 °C. Aluminum preferentially substitutes for zinc, with the variation in Mg content of ϕ being small (53.7-57 at.%). The maximum solubility of Zn in γ is about 8.3 at.% and that of Al in MgZn is also about 8.3 at.%.

Fig. 1
figure 1

Al-Mg-Zn isothermal section at 320 °C [2009Ren]

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Fig. 2
figure 2

Al-Mg-Zn isothermal section at 320 °C near the Mg corner [2009Ren]

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