The　depth　profiling　of　the　element　content　and　precipitation　phase　distribution　of　the　AA4045/AA3003mod　(Al-1.5Mn-0.35Cu　alloy)/AA4045　brazed　sheets　were　investigated　by　optical　microscope　observation,　electron　probe　microanalysis　(EPMA),　focused　ion　beam-scanning　transmission　electron　microscopy　(FIB-STEM).　The　electrochemical　test　and　sea　water　acetic　acid　test　(SWAAT)　were　performed　to　obtain　the　evolution　of　electrochemical　responses　and　corrosion　forms　of　brazed　sheet.　EPMA　results　showed　that　a　diffusion　layer　with　the　thickness　of　approximately　50　μm　existed　between　the　clad　layer　and　core　layer,　where　the　Cu　diffused　from　the　core　layer　and　Si　diffused　from　the　clad　layer.　It　was　found　that　brazing　led　to　a　significant　low　elements　solid　solution　area　at　the　end　of　the　Si　diffusion　path,　where　the　open　circuit　potential　was　lower　by　25　mV　comparing　to　the　unaffected　region.　Thus　the　diffusion　zone　can　provide　effective　cathodic　protection　to　the　unaffected　region　as　sacrificial　anode　by　the　potential　gradient.　The　SWAAT　analysis　revealed　the　corrosion　mechanism　of　the　residual　cladding　was　pitting　and　intergranular　corrosion.　This　area　with　high　density　of　intermetallic　compounds　and　Si　particles　increased　sensitivity　to　localized　attacks.　These　results　demonstrated　the　successful　application　of　the　FIB-STEM　system　in　illustrating　the　electrochemical　responses　and　corrosion　propagation　by　an　accurate　in-depth　characterization　of　intermetallic　particles　and　the　matrix　solid　solution.　©　2023　The　Authors