アルミニウムはんだ付部の耐食性について(第1報)

Abstract

The external cathodic polarization curves of each cast alloy such as Al-Sn, Al-Zn and Zn-Sn systems, which were dipped in 3% NaCl aqueous solution, were investigated by a potentiostatic method to determine the corrosion behavior of soft-soldered joint in aluminum. The profiles of the polarization curves were conventionally divided into two categories: straight line and curved line type. The former was seen in Al-Sn system only and this phenomenon was presumed as the cathode reaction of Eyring's protrotopic process, because the value of transfer coefficient calculated by using the measured value in this type was about 0.33 and was nearly equal to that of tin having a cathode control of activation process. The latter was seen in all of metals used as alloying elements and the remainder among the alloys tested here and this phenomenon was considered as the concentration polarization, where a cathode reaction is controlled by a diffusion process of dissolved oxygen. To do this consideration, iL, a limiting current density, was approximately calculated by the following equation introduced by using Fick's-Law.iL=2⋅F⋅D01/2[O2]⋅t-1/2/√πWhere F is Faraday constant, D0 is the diffusion constant of oxygen, [O2] is the concentration of disolved oxygen, t is the dipping time of sample. While the measured value for iL was decided by appling an overvoltage intercept method to the external cathodic polarization curve.From the electrochemical measurements mentioned above, it has been concluded that the natural electrode potentials of soldered joints in aluminum were not necessarily the important factor governing the corrosion rate between the aluminum, the various phases in the solder and the layer that forms at the aluminum and solder interface.