[NJARC] soldering Alum.

[AMCMATADOR at aol.com]

There is an old refrigeration trade technique for soldering aluminum. It 
dates back to the days when monitor top refrigerators were the order of the day, 
and cast aluminum freezer coils were as standard as the frustrated owner, who 
being impatient to wait for the ice to defrost would chip at it with an 
icepick, and invariably puncture the coils. The trick, is using conventional solder, 
melt a molten pool of it on the surface of the aluminum. Then, with the solder 
still hot, scratch vigorously  in the pool with a sharp implement, (scriber 
etc). The solder should form a halfway decent bond, and also provide decent 
conductivity. The reason for this is because aluminum oxidizes as soon as air 
(and moisture and impurities in the air) hits it. the solder, then sticks to the 
microscopic layer of oxide and not the aluminum when the solder is molten, and 
you scratch beneath the surface of the pool, the solder gets a chance to 
stick before the aluminum oxidizes again. A stainless steel scratching implement 
seems to work best. I wouldn't trust my life to a solder joint made this way, 
but it works quite satisfactorily. I learned this trick from a 90 yr. old, 
retired HVAC man. 

   Good Luck!