Abstract: A brazing sheet for vacuum brazing is provided wherein the sheet is cladded with an aluminum alloy brazing filler metal having a content of Mg sufficient for vacuum brazing but less than 1.2 wt. % and wherein the Mg.sub.2 Si particle size among Mg contained in the metal is not more than 5 .mu.m as a typical value.

Abstract: A vacuum pump is first driven to start evacuation from the interior of a furnace. At the time when the furnace pressure reaches 8.times.10.sup.-5 Torr, a heater is driven to start elevating the furnace temperature. Then, at the time when the furnace temperature reaches 565.degree. C. that corresponds to the solidus line temperature for a brazing filler metal of Al - 10% Si alloy containing Mg of 0.6 wt. %, a motor is driven to close a shutter, thereby vacuum brazing aluminum with evacuation control under a high-vacuum level. By controlling the evacuation after reaching a high-vacuum level, the amount of water vapor in the furnace becomes sufficiently small and Mg vapor is highly densified, which permits brazing of satisfactory quality even with a brazing filler metal containing Mg of 1.2 wt. % or less, in combination with use of such a brazing filler metal as having the Mg.sub.2 Si particle size fined to be 5 .mu.m as a typical value through soaking and the thickness of a surface oxide film thinned to be 80 .