Crack analysis near vacuum brazing interface of Cu/Al dissimilar materials using Al–Si brazing alloy

Abstract

The present paper concentrates on the factors inducing cracking near the Cu/Al vacuum brazing interface using Al–Si brazing alloy. Various analysis and test methods were adopted to analyse the cause of the cracking. Experiment results indicated that two intermetallic compounds layers – δ phase and θ phase – were formed near the interface of Cu and brazing seam region. The microhardness of both the two intermetallic compounds phases reached 720 and 510 HM respectively. The brazing seam region consisted mainly of θ phase and α-Al (Cu) solid solution. Si presence had led to obvious zone liquation in the brazing seam region. Stress concentration appeared on the margin and edge region of the joint. The crack initiated on the θ phase layer, and then extended towards the brazing seam region and δ phase layer. The separation in the θ phase had an obviously brittle fracture surface.

On the role of transmission electron microscopy for precipitation analysis in metallic materials

“…[209][210][211] For instance, the quantitative characterization of local chemical composition information surrounding precipitates, that is, interstitial and substitutional elements at the matrix-precipitate interface, during the early stage of precipitation is crucial for shedding light on the nucleation and growth mechanisms, and for improving the modeling of precipitation kinetics in metallic materials. For a long time, the quantitative chemical analyses of precipitates within bulk materials and of their interfaces by analytical TEM have been limited using conventional thin-foil specimen due to complex factors influencing the analysis accuracy, e.g., the difficulty in distinguishing signals from embedded precipitates and the matrix, the differential etching rate of phases during specimen preparation, [212] the effect of varying specimen thickness on beam spread, [213] and the influence of interface misorientation with respect to the electron beam on concentration profiles. [214] With the developments of advanced sample preparation methods and high resolution of EDS and EELS in advanced TEM, these issues can be combatted and a reliable chemical composition analysis by high resolution EDS or/and EELS analysis on FIB lamellae with very thin and uniform thickness is now possible.…”

Formation and evolution of intermetallic compounds at interfaces of Cu/Al joints by ultrasonic-assisted soldering

“…However, intermetallic compounds (IMCs) usually form at the interface of joints fabricated by means of almost every welding method, including soldering (Xia et al, 2009), cold pressure welding (Abbasiet et al, 2001), bonding (Xu et al, 2011) or friction stir welding (Abdollah-Zadeh et al, 2008;Ouyang et al, 2006). The IMCs dramatically harm the performance of the joints because of their poor mechanical properties.…”

“…The high strength may result from a very thin IMC layer. When Xia et al (2008;2009) soldered copper and aluminum in a vacuum furnace using Al-Si solders, the IMC layer on copper was as thick as 20 μm.…”

Reliability studies of Cu/Al joints brazed with Zn–Al–Ce filler metals

“…Moreover, brazing is applicable to manufacture of components with complicated shapes and for processing in mass production [7]. Xia et al [8] joined Cu and Al using vacuum brazing with a eutectic Al-12Si filler metal, and studied the microstructure and phase constitution near the interface of the Cu/Al joints. Cu 3 Al 2 and CuAl 2 phases were found in the interface of the copper and brazing seam region.…”