高溫無鉛銲料在3.5% NaCl溶液之電化學腐蝕行為

Electrochemical Corrosion Behavior of High Temperature Pb-free Solders in 3.5% NaCl Solution

本研究探討新型高溫無鉛銲料Bi-11 wt.% Ag及Zn-40 wt.% Sn於3.5% NaCl水溶液極化行為，並與Pb-5 wt.% Sn進行比較。實驗結果發現Bi-11Ag具有兩個鈍化區，Pb-5Sn存在一個較大的鈍化區，而Zn-40Sn則沒有鈍化區的產生。腐蝕電位順序為Bi-11Ag > Pb-5Sn> Zn-40Sn，電流密度則是Zn-40Sn試片最大，Pb-Sn最小。由XPS與XRD分析結果得知Bi-11Ag鈍化層為Bi2O3及BiOCl，當掃描電位至+2000 mV時，表面腐蝕物為Bi2O3、BiOCl與AgCl；Pb-5Sn表面腐蝕物主要為PbCl2、PbO以及Sn的氧化物，外側富氧、內側Cl含量較高；Zn-40Sn腐蝕物極表面由ZnO與ZnCl2組成，次表面才偵測到Sn的氧化物。本研究亦證實添加Ag於純Bi中可改善抗腐蝕性，原因為延展性與耐蝕性俱佳之富Ag顆粒散佈於Bi基地，可調適並降低因鈍化層生成所造成的壓應力，可避免鈍化層過早崩潰。

This study aimed at investigating the electrochemical corrosion behavior of novel Pb-free solders, Bi-11 wt.% Ag and Zn-40 wt.% Sn, in 3.5% NaCl solutions using the potentiodynamic polarization method with scanned potentials ranging from -2000 mV to +2000 mV. A Pb-5 wt.% Sn alloy was also examined for comparison. Experimental results showed that the order of the selected solders in terms of corrosion potential (Ecorr) from noble to active was Bi-11Ag, Pb-5Sn, and Zn-40Sn. The corrosion current density (icorr) of Zn-40Sn was the highest, and that of Pb-5Sn was the lowest. The Pb-5Sn sample had a more extended passive region compared to Bi-11Ag, while the Zn-40Sn sample did not showed passive behavior within the scanned potential range. According to the XPS and XRD data, the corrosion products were mainly PbCl2 and PbO for Pb- 5Sn and BiOCl, AgCl2, and Bi2O3 for Bi-11Ag. Zn rich phases (ZnO and ZnCl2) were found on the polarized surface of Zn-40Sn, and tin oxides were detected at the subsurface. It was also demonstrated that an addition of Ag led to an increase in passivation ability of Bi, which could be ascribed to the ductile Ag-rich nodules embedded in the Bi matrix. The matrix was then capable of accommodating compressive stresses stemming from the formation of passive films and thus preventing an early loss of passivity.