Intrinsic Diffusivities Ratio Analysis in the Al-Cu System

Abstract

Copper and aluminium electric corrosion rates are investigated experimentally at room temperature and at temperature 100oC. It is founded that copper corrosion is higher than aluminium corrosion, and ratio of electric corrosion rates, kCu/kAl , decreases with temperature increasing. It is calculated that copper corrosion rate is approximately equal to aluminium corrosion at temperature about 300oC due to Cu2+ ions are less mobile than Cu+ ions. It is obvious physically: the higher temperature is, the grater atoms’ displacements in crystal lattice, Cu atoms can diffuse without two electrons, and Cu2+ ions more strongly interact with crystal lattice than Cu+ ions. A theoretical method to calculate intrinsic diffusivities ratio in double multiphase systems is proposed. The method involves the Kirkendall plane displacement and the general phases thickness only. Intrinsic diffusivities ratios in the Al-Cu system are calculated using literature experimental data. Diffusion activation energies and pre-exponential coefficients for the Cu-Al system are calculated combining literature experimental results. Analysis of literature data shows that the Kirkendall shift changes sign at temperature about 460oC in the Cu-Al system because of intrinsic diffusivities ratio, DCu*/DAl*, dependence from temperature. Such result agrees with copper and aluminium electric corrosion rates investigation.

Keywords

• diffusion
• intermetallic compounds
• phases formation kinetics
• copper
• aluminium
• the kirkendall-frenkel porosity
• the kirkendall shift