Effect of Cu and Mg on the corrosion behavior of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum alloy brazing sheet

Abstract

Higher strength and better corrosion resistance are necessary to enable the thickness reduction of the aluminum alloy brazing sheets. In this work, an age-hardenable Al-Mn-Cu-Mg-Si core alloy was developed by the addition of Mg, Si and Cu. The corrosion behavior of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum alloy brazing sheet in sea water acidified accelerated test (SWAAT) was investigated and compared with the traditional 4004/3003/4004 aluminum alloy brazing sheet. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). After brazing, it was found that the microstructures of two aluminum alloy brazing sheets from outer to the center were precipitate-free zone (PFZ), the band of dense precipitates (BDP) and core material, respectively. In particular, both Cu and Mg concentration gradients were formed in the BDP region of 4004/Al-Mn-Cu-Mg-Si/4004. Moreover, the SWAAT results showed exfoliation corrosion in 4004/Al-Mn-Cu-Mg-Si/4004, while in 4004/3003/4004, severe inter-granular corrosion in core material was observed after corrosion for 584 h. The theoretical electric potential distribution showed that the presence of Cu and Mg concentration gradient promoted the formation of the electric potential trough in the BDP region, which may be the reason for the occurrence of exfoliation corrosion in 4004/Al-Mn-Cu-Mg-Si/4004.