Effects of vacuum brazing on microstructure and corrosion of 3003 aluminum alloy welding seam

The paper aims to study influences of brazing temperature and heat preservation time on the weld microstructure and corrosion behavior of 3003 aluminum alloy, and predict weld corrosion life of 3003 aluminum alloy through model. In the simulated marine atmosphere, salt spray corrosion method was used to observe micro-morphology and element distribution of weld seam in combination with SEM and EDS. According to the corrosion weight loss and maximum pitting depth, the corrosion resistance of weld was analyzed. A corrosion dynamic model was established. The micro-morphology and element distribution of weld seam was calculated in reference of outdoor exposure corrosion data to predict the corrosion life. The results showed that when the vacuum degree was 3×10-3 Pa, with the increase of brazing temperature and prolonging of holding time, the segregation of Si in weld zone was reduced, and the corrosion resistance of the weld was enhanced. Whenthe brazing temperature was kept at 610°C for 75 min, the weld microstructure was the most uniform, mainly composed of Al and Si element, and contained a small amount Mn and Mg element. And the weld also contained Al-Mn, Mg2Si and Al3Mg2 alloy phases. The dynamic equations of the corrosion weight loss and the maximum pitting depth of the weld were y1=0.0642t0.897 and y2=0.03t1.63, respectively. Compared with the corrosion kinetics equation of LY12 aluminum alloy in Qionghai for exposure of 10 years, the corrosion equivalent coefficient was 13.39. The maximum corrosion equivalent depth was 87.9 µm in Qionghai for exposure of 10 years. The Si segregation in weld zone has important influences on the corrosion performance. The best brazing condition is that the brazing temperature is 610°C, and the holding time is 75 min. At this time, the corrosion equivalent depth of weld accounts for 87.9 percent of weld thickness 100 µm after 100 years of atmospheric corrosion, which could meet the requirement of 10 years of corrosion life. When brazing temperature is increased and holding time is prolonged, corrosion occurs to the interface between the substrate and weld, and the corrosion resistance is weakened. © 2018, Chongqing Wujiu Periodicals Press. All rights reserved.