Effect of Zn and Mg alloying on microstructure and anticorrosion mechanisms of Al-Si based coatings for high strength steel

The effect of Zn and Mg alloying on the microstructure and anticorrosion mechanisms of AlSi coatings for steel was studied combining electrochemical tests, material balance after accelerated corrosion tests, visual observation, phase identification on corroded and uncorroded surfaces by X-ray diffraction, Raman spectroscopy and electron microscopy. Zn alloying promoted an AlZn solid solution therefore improving sacrificial protection of steel at first cycles of the test. With cycling, the AlSiZn coatings were rapidly consumed by selective dissolution of AlZn coupled with cathodic Si. Additional Mg alloying increased the coating life, binding Si in more anodic Mg2Si and stabilizing corrosion products.