Quaternary Diffusion in 7000 Aluminum Alloys

Abstract

Quaternary and ternary interdiffusion experiments of 7000 aluminum alloys have been performed at 725 and 755 K. The concentration profiles indicate that the diffusion distance of Cu is shorter than those of Zn and Mg in the solid solutions. The direct interdiffusion coefficients \\ ildeD_ZnZn^Al, \\ ildeD_MgMg^Al are positive, and indirect coefficients \\ ildeD_ZnMg^Al, \\ ildeD_MgZn^Al are negative in the ternary Al–Zn–Mg alloys. The effective interdiffusion coefficients in 7000 aluminum alloys are in the order \\ ildeD_Zn,C^eff>\\ ildeD_Mg,C^eff>\\ ildeD_Cu,C^eff. When the concentration distribution of Zn and Mg are almost constant and the concentration of Cu approaches zero in the Al–Zn–Mg/Al–Zn–Mg–Cu couple, it is obvious that \\ ildeD_Cu,C^eff=\\ ildeD_CuCu⁴=\\ ildeD_{Cu(Al–Zn–Mg)}^∗. The ratio values of indirect to direct diffusion coefficients suggest that attractive interactions of Zn–Mg and Cu–Mg exist in the Al–Zn–Mg–Cu alloys.