The Rietveld X-ray diffraction analysis was applied to analyze the weight fraction of precipitation phases and microstructure characterizations of rapidly solidified Al-8Zn-4Mg- Cu, = 1, 4, 8, and 10 alloys (in wt.%), prepared by melt spun technique. A good agreement between observed and calculated diffraction pattern was obtained and the conventional Rietveld factors ( , , and GOF) converged to satisfactory values. Solid solubilities of Zn, Mg, and Cu in α-Al were extended to high values. Besides, metastable Al0.71Zn0.29, intermetallic Al2CuMg, Al2Cu, and CuMgZn phases have been observed for = 4, 8, and 10 Cu alloys. The crystal structure and microstructure characterizations exhibit strong Cu content dependence. 1. Introduction The main attributes of rapid solidification are the extension of solid solution, refinement of structures in the nanometer range, production of fine dispersion of the second phase, synthesis of novel crystalline, and amorphous phases [1–4]. The Al-Zn alloys fulfill a significant fraction of industry’s demand for the development of lightweight materials having high strength and toughness characteristics. Cu was added into the 7000 alloys to improve the stress corrosion cracking resistance [5, 6]. 7xxx series (Al-Zn-Mg-Cu) aluminum alloys are widely used in the aircraft industry due to their low density and high strength [7]. It was reported that several intermetallic phases such as (MgZn2), (Al2Mg3Zn3), (Al2CuMg), and (Al2Cu) can occur below the solidus [8–10]. The interaction in Al-Zn alloys is rather weak and Zn atoms (atomic radius 1.39？？) do not tend to form intermetallic phases with Al atoms (atomic radius 1.43？？), which means that this size difference has a great influence upon the crystalline microstructure of Al-Zn alloys [11]. However, metastable Al0.71Zn0.29 phase has been observed by the author in melt spun Zn-22wt.%Al-6wt.%Ce [12]. This metastable phase disappeared by annealing (300°C/20？h) and has been also observed by others [13, 14]. Rietveld method is becoming progressively more popular for microstructure characterization of materials. It is common practice to estimate domain size and strain values from the refined profile width parameters. Moreover, weight fractions of all phases in multiphase sample can be calculated directly by their scale factors which can be obtained by Rietveld fitting. The relationship between relative weight fraction ( ) of each phase in a mixture of phases and its Rietveld scale factor ( ) can be obtained by the following relation [15]: where , , and are number of formula units per cell,
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