Activation of an Al-Zn-Mg-Li alloy by the presence of precipitates to be used as sacrificial anode

摘要

This work reports the influence of microstructure on the electrochemical efficiency of Al-alloys to be used as sacrificial anodes. The microstructure of as-cast Al-ingots was characterized by X-ray diffractometry and scanning electron microscope (equipped with WDS microanalysis facilities). The electrochemical behavior was investigated in 3% NaCl solution simulating sea water at room temperature. Regarding microstructure, X-ray diffractometry detected the presence of the α-Al phase, and the τ-Al{sub}2Mg{sub}3Zn{sub}3, Mg{sub}7Zn{sub}3 and δ-AlLi precipitates. SEM observations confirmed the presence of α-Al dendrites with τ-Al{sub}2Mg{sub}3Zn{sub}3 and Mg{sub}7Zn{sub}3 particles in matrix. In interdendritic regions, it was observed the presence of the eutectic α-Al+τ-Al{sub}2Mg{sub}3Zn{sub}3 plus some primary Mg{sub}7Zn{sub}3 particles. δ-AlLi particles were identified at this step only by X-ray diffractometry. Finally, it was detected that an uniform distribution of precipitates in the α-Al dendrites together with an uniform distribution of a fine eutectic gave as a result in as-cast ingots an electrochemical efficiency up to 61.4 %.