Microstructural analysis of germanium modified tin-copper brazing filler metals for transient liquid phase bonding of aluminium

摘要

The present contribution summarises first results that have been achieved with the new brazing material Sn75Cu20Ge5 (wt-%) for transient liquid phase (TLP) bonding of aluminium cast alloy AlSi7Mg0.3 (wt-%). The microstructure of the braze ribbons and the obtained joints have been thoroughly investigated on different length-scales using scanning and transmission electron microscopy as well. Whereas the braze ribbon material is only composed of beta-tin, eta-phase (Cu6Sn5) and some germanium rich precipitates, the transient liquid phase joint displays a much more complex microstructure that consist mainly of beta-tin and different aluminium-copper and aluminium-germanium phases. In addition small silicon oxide rods and a hitherto unreported hexagonal aluminium-copper-magnesium-germanium phase with approximated lattice parameters a = 0.7123 nm, c = 2.40 nm have been found in the seam of the joint.