Applicability and limitations of using online non-destructive UV-vis spectrophotometer to monitor the dissolution of an Al-Zn-Mg-Cu alloy in HCl-containing solution were studied. ICP-AES results indicate that the spectrum absorbance at 252 nm is mainly attributed to Cu-containing complexes. Surprisingly, an hours-long “induction” period was observed from UV-vis results. This is not a real indicator of induction for Al dissolution as revealed by electrochemical impedance spectrum, actually it reflects the alloy's galvanic corrosion nature that Cu species are released after Al, Zn, Mg species.