Removing aluminum oxide before galvanic current and potential measurements
sure it's going to affect the test so you have to remove the oxide layer 
Generally, we adopt the method of alkali corrosion to remove the oxide layer on the surface of the aluminum.The purpose of alkali corrosion is removing the oxide layer on the surface of the aluminum. (Note: Technological process of the method is as follows: under normal temperature, 20% nitric acid; the process parameters is about 0.5 minutes. Pre-degrease--degrease--rinsing--rinsing--alkali corrosion--rinsing--rinsing--bright dipping--rinsing--rinsing--pure rinsing. The purpose of bright dipping is to remove surface residual black ash after alkali corrosion.Temperature:50-60 degrees; time:0.5-1 minutes.The purpose of degreasing is to remove grease on the surface of the aluminum.The process parameters is 0.5-1 minutes. You can use acid to wash it