My great grand father, who worked in the Birmingham jewellery industry in the nineteenth century, could solder aluminium. An uncle of mine, a metallurgist, analysed one of his joints and deemed it worked and was sound. Typically his knowledge died with him.
I have seen demonstrations of aluminium soldering where the oxide layer is scratched away by a stainless steel wire brush. However I do not know of anyone successfully using such a solder. To make me more suspicious, during my working life as an engineer I have not been aware of aluminium solder being used in industry.
As an aside the firm I worked for did braze up cracks in high temperature alloys containing about 5% aluminium. The flux used was gaseous HF.
AVTUR
