Corrosion Mechanisms in Brazed Al-Base Alloy Sandwich Structures as a Function of Braze Alloy and Process Variables
Final rept. 27 Mar 2006-31 Dec 2012
VIRGINIA UNIV CHARLOTTESVILLE OFFICE OF SPONSORED PROGRAMS
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14 AA 6061 UNS A96061 and AA4047 UNS A94047 were brazed to construct a tapered modelbraze joint with variable braze clearance. Isolated AA 6061 T6 was also exposed to the thermal cycle of a typical dip brazing process without applying filler metal. The braze, mixed, and heat affected zones were modeled by thermochemical computations and characterized experimentally. Corrosion exposures were conducted in accordance with BS 11846 Method B for detection of intergranular corrosion IGC. Each zone developed its own corrosion morphology traced to the unique chemical composition and metallurgical characteristics. The brazing thermal cycle promoted IGC of isolated AA 6061. Moreover, the Al-Si braze and AA 6061 joint promoted additional intergranular corrosion in the Si containing mixed zone exacerbated by grain boundary Q AI4Cu2Mg8Si7 and phases as well as eutectically formed Sineedles at solidification boundaries. Pitting occurred in the Al-Si braze zone.
- Metallurgy and Metallography