Corrosion of brazed joints with aluminum-based filler metals in vacuum

Four kinds of brazed joints brazing with Al-Si-Cu filler metals in vacuum were corroded in 3.5 pct NaCl solution.The microstructures,corrosion patterns,as well as the segregation and diffusion of Cu element in the grain boundary of the as-corroded joints were investigated,and a corrosion mechanism was proposed.The results showed that corrosions such as pitting and intergranular corrosion still existed in the brazed joints,and the corrosion contaminants were AlCl₃,Al(OH)₃ and Al(OH)₂Cl.As Cu content in the Al-Si-Cu filler metals increased,the corrosion of the joints became more serious.It was found that the segregation and diffusion of Cu element significantly affected the corrosion characte-ristics.A poor Cu element area was observed nearby grain boundary,and Al₂Cu phase was found on the grain boundary.Because of the potential difference between the grain and grain boundary,a local corrosion cell was formed and resulted in the intergranular corrosion of the joint.