Aluminum solder consists of aluminum, phosphor-tin, zinc, antimony, and an acid. In forming the solder, the zinc, tin, and antimony should be melted before the acid is added. The following flux should be used in soldering aluminum: 12 oz. zinc chloride, 1 oz. sal ammoniac, and 13 oz. water.
Zinc chloride as a flux is made by adding zinc shavings or pieces to muriatic acid until the bubbles have disappeared. The zinc chloride formed in this way is often called cut-acid or killed (neutralized) acid to distinguish it from the muriatic acid, which is also used as a flux.
An acid flux, like muriatic acid and zinc chloride, should never be used on an electrical connection or on any article that is to be painted. An alcoholic solution of rosin is a good flux for this work.