La添加によるAl-10%Si-2%Cu合金の腐食特性の向上

Enhancement of the Corrosion Properties of Al-10%Si-2%Cu Alloys with La Addition.

抄録

Al-10%Si-2%Cu合金は比重が小さいため、航空宇宙や自動車などの高付加価値産業で広く使用されているが、ガルバニック腐食により耐食性が低下する。そこで、Al-10%Si-2%Cu合金の微細組織と腐食特性をランタン(La)含有量に応じて調べた。すべてのAl合金試料は重力鋳造法を用いて合成され、La添加量は0.00、0.25、0.50、0.75、1.00 wt%であり、組織特性分析および電気化学試験を用いて特性評価を行った。0.5wt%のLa添加(xLa-0.5)は最も微細な組織を示し、Laを含まない合金(xLa-0)よりもα-Al面積率が4%低かった。しかし、1 wt%La添加合金(xLa-1)の面積率はxLa-0より2.4%高かった。xLa-0.5の腐食電流密度()は1.09μA/cmで、xLa-0に比べて68%減少し、xLa-0.5が最も高い分極抵抗値(7.32×10Ω・cm)を示した。xLa-0.5の耐食性向上は、微細構造による不動態化層の迅速かつ緻密な形成と、Cuの分散性向上による析出相によるものである。

Al-10%Si-2%Cu alloys have been widely used in high-value industries (e.g., aerospace and automobiles) because of their lower specific gravity; however, galvanic corrosion rendered these alloys to have poor corrosion resistance. Therefore, the microstructure and corrosion properties of Al-10%Si-2%Cu alloys were investigated with respect to the lanthanum (La) content. All Al alloy samples were synthesized using gravity casting, with added La contents of 0.00, 0.25, 0.50, 0.75, and 1.00 wt%, and were characterized using microstructural characteristics analysis and electrochemical tests. Adding 0.5 wt% La (xLa-0.5) indicated the finest structure, which had a 4% lower α-Al area fraction than the La-free alloy (xLa-0). However, the area fraction of a 1 wt% La-added (xLa-1) alloy was 2.4% higher than that of xLa-0. The corrosion current density () of the xLa-0.5 was 1.09 μA/cm, representing a 68% decrease as compared to that of xLa-0, and xLa-0.5 reached the highest polarization resistance value (7.32 × 10 Ω·cm). The improvement in corrosion resistance of xLa-0.5 was due to the rapid and dense formation of a passivation layer induced by its fine structure, as well as the precipitated phase by enhancing the dispersibility of Cu.