亜鉛拡散処理アルミニウム合金管の腐食挙動について

抄録

Corrosion behavior of 1050 and 3003 aluminum alloy tubes with Zn diffusion layers in the surfaces was studied by intermittent spray and total immersion tests. A correlation was found between the Zn diffusion gradients and corrosion behavior of the alloys. In those tubes with suitably thick diffusion layers and adequately steep gradients of Zn concentration, only general dissolution occurred after a long test period. In the tubes covered by very thin layers with high Zn gradients, the layers were consumed within a short time and then pitting corrosion generated. On the contrary, pitting corrosion occurred even in the diffusion layers when the gradients were very low. A comparison was also made to clarify the difference in corrosion behavior between the Zn diffused tubes and the alclad 3003 alloy tubes. Pitting occurred in the 7072 alloy clad and pits penetrated into the 3003 core, and this suggested that the effective region of the sacrifitial anode action of 7072 alloy clad might be restricted within a limited area by the environmental conditions such as the electrical conductivity of the solution in contact with the alloy-surface and the thickness of the solution film.