STUDY OF THE BRAZEABILITY OF ALUMINUM-MATRIX COMPOSITES

The brazeability of several aluminum matrix composites has been evalua ted in the present paper. Tested materials were two different 6061 alu minum alloys, reinforced with 10 and 20% alumina particles, respective ly, and a 7005 aluminum alloy containing 10% alumina also in the form of discrete particles. A drop formation test was selected to evaluate the brazeability of the studied composites, using a commercial filler metal (BAISi4) generally used for brazing of aluminum alloys. Wettabil ity of molten braze on the metal matrix composites (MMCs) was determin ed by measurement of the solidified contact angle in sessile drop test s and determination of the spread area. The wettability and spreading increase with the brazing temperature in the studied range (550-625 de grees C, 1022-1157 degrees F), and decrease when the reinforcement pro portion is increased. Both properties are also influenced by the type of the composite aluminum matrix being enhanced in the Al-Zn-Mg reinfo rced alloy. This study was completed with the microstructural characte rization of the drop test specimens and of real brazed joints made on ''T-shaped'' specimens. The influence of postbrazing heat treatment wa s also studied. Shear mechanical tests were conducted out on brazed ov erlap specimens to determine the joint strength and values controlled by the strength of the brazing filler metal used. Maximum shear streng ths higher than 90% of the nominal BAISi4 filler metal shear strength were obtained for both composites reinforced with 10% of alumina parti cles, representing nearly 50% of the strength of these composites.