To rapidly absorb heat generated when welding or brazing, and prevent the deformation of a matrix by compounding aluminium, copper and their alloy powder and pieces with a heat insulator.

50% of a water-containing bentonite heat insulating agent with which, for example, 2.5wt.% to 10wt.% (hereinunder wt.% is omitted) of aluminum, copper and their alloy powder and pieces are mixed, is prepared, and this agent is put on a circumference to be welded or brazed in thickness of about 8mm and width of about 30mm, and processed to be welded or brazed. Or, about 5% of an aluminum piece (about 30% mesh) and about 50% of copper and brass powder (about 200 mesh) are mixed with 50% of the water-containing bentonite heat insulating agent, and it is put on a welding piece outside about 3mm from the welding part in thickness of about 8mm and width of about 30mm so as to execute welding. Hereby, the deformation of a matrix accompanied by welding can be prevented.