Effect of Sr addition on corrosion behavior of Al-Si-Zn brazing alloy

Objective The corrosion properties and mechanism of Al-Si-Zn brazing alloy with different Sr addition were studied. Methods By combining theory and experiment, based on the First-principles, the influence of Sr on the dissolution potential of Al-Si-Zn alloy was investigated. By means of electrochemical testing, scanning electron microscopy and energy spectrum analysis, the surface morphology and the polarization curves of open circuit potential and electromotive potential of Al-Si-Zn alloy with different Sr addition in 3.5% NaCl solution potential were studied. Results The results showed that when the coverage of Al-Zn(100) surface containing Sr increases from 0.25 ML to 0.75 ML, the chemical potential of Al-Zn on the surface increased by 0.13～0.93 eV compared with that without Sr, and potential of the dissolved electrode of Al-Zn atom on the surface also shifted to a negative direction, indicating that Al-Zn(100) containing Sr became more easily corroded.The Mulliken charge population on the surface indicated that the total negative charge number of Al atom in the surface layer increases with the increase of Sr coverage on the surface, it was shown that the decrease of work function makes Al more active, so it was easier to produce electrochemical corrosion reaction. Conclusion Al-Si-Zn-xSr brazing was electrolytically corroded in 3.5% NaCl solution. The corrosion performance of brazing metals decreased compared with that without Sr. When the addition of Sr element was 0.4 %, the corrosion resistance of the brazing metal was the best.