Al-Cu-Zn (Aluminum-Copper-Zinc)

Abstract

The previous update on this ternary system by [2007Rag] reviewed mainly the thermodynamic assessment of [1998Lia]. Very recently, [2009Ren] determined a partial isothermal section at 360°C for Cu-lean alloys and found that Cu stabilizes the miscibility gap of the Al-Zn fcc phase. Binary SystemsThe Al-Cu phase diagram [2004Ria] depicts the following intermediate phases: CuAl 2 (C16-type tetragonal, denoted h), CuAl(HT) (g 1 , orthorhombic) CuAl(LT) (g 2 , monoclinic), Cu 5 Al 4 (HT) (f 1 , orthorhombic, space group Fmm2), Cu 5 Al 4 (LT) (f 2 , orthorhombic, space group Imm2), e 1 (HT) (cubic?), e 2 (LT) (B8 1 , NiAs-type hexagonal), Cu 3 Al 2 (rhombohedral), Cu 9 Al 4 (HT) (c 0 , D8 2 , Cu 5 Zn 8 -type cubic), Cu 9 Al 4 (LT) (c 1 , D8 3 , Cu 9 Al 4 -type cubic), and Cu 3 Al (b, bcc). The Al-Zn phase diagram [1993Che] 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 fcc 1 and fcc 2 . The monotectoid reaction fcc 2 M fcc 1 + (Zn) follows at 277°C. The Cu-Zn phase diagram [1993Kow, Massalski2] is characterized by a series of peritectic reactions, which yield CuZn (b, bcc), Cu 5 Zn 8 (c, D8 2 -type cubic), CuZn 3 (d, B2, CsCl-type cubic), and CuZn 4 (e, cph). Zn (cph) has a c/a axial ratio much larger than e and the two coexisting cph phases are modeled separately with different interaction parameters [1993Kow]. The b phase orders to a CsCl-type B2 phase (b¢) through a second-order transition below $460°C. Ternary PhasesA ternary phase with rhombohedral symmetry and with the nominal composition Al 4 Cu 3 Zn (denoted s) is known in this system [Pearson3]. The homogeneity range of s and its temperature dependence are not clearly defined. The structurally-related, low-temperature form s¢ was found to be stable by [2005Hao] between 400°C and room temperature. Ternary Phase EquilibriaWith starting metals of 99.999% purity, [2009Ren] prepared diffusion couples of Cu-Zn master alloys with pure Al. The diffusion couples were annealed at 360°C for 48 h and quenched in water. The coexisting phase compositions were measured by electron probe microanalysis and listed. The isothermal section at 360°C constructed by [2009Ren] is shown in Fig. 1. In the Al-Zn system, the miscibility gap in the fcc phase closes at 351°C. The addition of Cu stabilizes this gap, which is stable at 360°C, even with as low as 0.1 at.% addition of Cu. The gap increases in width with increasing Cu content. In an earlier study, [2004Ren] determined tie-lines between fcc 1 and fcc 2 at 340 and 320°C for small additions of Cu and these are shown in Fig. 2. The Cu addition shifts the fcc 1 /(fcc 1 + fcc 2 ) and (fcc 1 + fcc 2 )/fcc 2 phase boundaries towards the Al-rich corner. Also, Cu segregates in the fcc 2 phase in preference to fcc 1 .The computed results of [2009Dai] indicate that the stabilizing effect of Cu on the Al-Zn miscibility gap increases with increasing Cu content, culminating in a metastable miscibility gap in the Al-Cu binary system...

Interfacial reactions of Sn–Zn–Ag–Cu alloy on soldered Al/Cu and Al/Al joints

“…Cu 5 Zn 8 was found in the core of the large precipitates . This Cu 5 Zn 8 was dissolved in Al, forming Cu 9 Al 4 (as follows from the phase diagram of Al-Cu-Zn) [25], which in turn was surrounded by the outermost AgZn 3 phase. After 144 h, only small AgZn 3 precipitates and fine precipitates of Cu 9 Al 4 were present.…”

“…In the case of the Al/SnZn0.5Ag1.0Cu/Cu joint, dissolution of Al substrate was observed. From the side of the Cu substrate, a thin layer containing Cu, Al and Zn was formed, corresponding to the Cu 9 Al 4 and γ -phase according to the Al-Zn-Cu phase diagram [25]. In the joint, large precipitates composed of Cu 5 Zn 8 and AgZn 3 IMCs were found, accompanied by small Ag-Zn precipitates in the eutectic SnZn matrix.…”

Zn diffusion and reflow behaviour of Sn-9Zn and Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solders on a Ni/Cu substrate under IR reflow

“…This may be one of the reasons for the non-formation of the Ni-Zn IMC at the interface similar to the Sn-9Zn/Ni/Cu system (Mittal et al, 2009). Cu-Sn compounds were also not found to form at the interface; this is because of the reaction of Al with Zn and Cu and formation of an Al-Cu-Zn compound, as in Sn-Zn-Al/Cu system (Raghavan, 2007).…”