Preparation And Prorperties Of High-strenatn Al-based Brazing Filler Alloys With Low Melting Point

Braze welding is one of the most commonly used technologies for joining aluminum alloys. Up to now, brazing with the Al-12Si filler metal has been recognized as the main method for joining aluminum components. However, due to the high melting temperature, the traditional filler metal has to work above590℃, which would engender the melting erosion of aluminum alloy. In this paper, the effect of Si, Cu etc on the melting temperature, brazability, corrosion resistance etc of the filler metals had been systematically investigated. The properties of filler metals prepared by arc melting and rapid solidification were compared and analyzed. The filler metals for brazing aluminum alloy with a melting point lower than500℃were studied out. Differential scanning calorimeter (DSC), scanning electron microscopy (SEM) and electrochemical method were used to investigate the melting temperature, microstructure and corrosion resistance, respectively. The brazability and joint shear strength were tested in according to the standard of GB/T11364-2008and GB/T11363-2008separately. The results are summarized as follows:The solidus temperature of the Al-9.6Si-20Cu-xGe (0≤x≤20wt.%) filler metals was decreased as addition of germanium, and the reason was that volume fraction of low melting point eutectic was raised in alloy; while the liquidus temperature exhibited an different variation law. The solidus and liquidus temperature of the Al-ySi-20Cu-15Ge (6.5<y<9.6%) filler metals were both decreased with silicon dropped from9.6%to6.5%. the solidus and liquidus temperature were451.1℃and492.1℃separately with the silicon content of6.5%. The solidus temperature of the Al-9.6Si-20Cu-10Ge filler metal was decreased as the addition of tin and zinc, which was due to the low melting point of tin and zinc that could reduce the melting temperature of the low melting point eutectic in the alloy. The liquidus temperature fell to498.6℃by adding4%tin, then rose as the increasing of tin content. The liquidus temperature of the Al-9.6Si-20Cu-10Ge-6Zn filler metal was493.5℃. Owing to smaller grain size, the melting temperature of filler metals that prepared by rapid solidification were lower than arc melting.The Al-9.6Si-20Cu-nGe (0≤n≤15%) filler metals displayed an active behavior in NaCl neutral solution. Ecorr of the filler metal was decreased as increasing the germanium content. While the corrosion current density reached the lowest value by adding5%germanium. The preferential dissolution area was a(Al) in the vicinity of the Al2Cu phase grains.The joints of Al-9.6Si-20Cu-10Ge-4Sn filler metal with different brazing temperature and holding time had the same microstructure, consisted of the α(Al) solid solution, Si-Ge particle and Al2Cu intermetallic compound. If holding time was fixed, the interface boundary of the joint changed into irregular wave-like with increasing of the brazing temperature, the same variation law as brazing temperature was fixed at540℃by prolonging holding time. With different brazing temperature and holding time, the fracture areas were both happened at weld seam. Brittle fracture surface appeared in some brittle Si-Ge particles and Al2Cu intermetallic compounds, which resulted in the weakening of the mechanical properties of brazing joints. Volume fraction of a(Al) solid solution was improved at the interface as holding time prolonged, and the joining strength were increased.