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Effects of Brazing Time and Temperature on the Microstructure and Mechanical Properties of Aluminum Air Brazed Joints
Author(s) -
Kim Jin Yong,
Weil K. Scott
Publication year - 2007
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.02075.x
Subject(s) - brazing , materials science , microstructure , foil method , joint (building) , sintering , ductility (earth science) , aluminium , metallurgy , composite material , layer (electronics) , oxide , substrate (aquarium) , fracture (geology) , creep , alloy , architectural engineering , oceanography , engineering , geology
High‐purity aluminum foil was used to join alumina substrates directly in air at temperatures ranging from 800° to 1200°C and soak times of 1–100 h. It was found that the bend strengths of the resulting Al 2 O 3 /Al/Al 2 O 3 joints generally increase with increasing brazing temperature and time, with a maximum bend strength of 135 MPa on average achieved in samples joined at 1200°C for 100 h. Additionally it was determined that measurable ductility is retained in the joint even after exposure under extended high‐temperature conditions. During joining, an Al 2 O 3 scale forms along the interface between the aluminum and adjacent substrates. An increase in brazing temperature and/or time leads to intergrowth and sintering between this thermally grown oxide layer and the substrate surface, which appears to be the primary source of improved joint strength. Fracture analysis indicates that the Al 2 O 3 /Al/Al 2 O 3 joints generally fail via one of three mechanisms, (1) by de‐bonding along the foil/substrate interface in specimens that were joined at low temperature or held at temperature for an insufficient period of time; (2) by ductile rupture in specimens that were joined at conditions that promoted sintering between the oxidized foil and adjacent alumina faying surfaces, but left behind a continuous residual aluminum layer within the joint; or (3) by mixed‐mode fracture in specimens joined at high temperature and long exposure times, in which the thermally grown alumina that forms between the two substrates is interrupted by dispersed pockets of residual aluminum metal.