Quaternary Diffusion in the α Solid Solutions of Al–Zn–Mg–Cu Alloys

Abstract

Quaternary interdiffusion experiments of Al-rich α Al–Zn–Mg–Cu alloys have been performed in the temperature range from 755 to 833 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_ZnZn⁴, \ ildeD_MgMg⁴ and \ ildeD_CuCu⁴ are positive, and indirect coefficients are negative. The impurity diffusion coefficients of Zn (or Cu) in Al–Cu (or Zn)–Mg alloys can be expressed by the following equations.
D_{Zn(Al–1.15Cu–2.01Mg)}^*=3.9×10⁻⁵exp(−124kJ mol⁻¹⁄RT⁻¹)m²⁄s,
D_{Cu(Al–3.37Zn–2.75Mg)}^*=5.7×10⁻⁵exp(−132kJ mol⁻¹⁄RT⁻¹)m²⁄s.
The ratio values of indirect to direct diffusion coefficients suggest that attractive interactions of Zn–Mg, Zn–Cu and Cu–Mg atoms exist in the Al–Zn–Mg–Cu alloys.