For sheet aluminum an iron tin solder may be used with a flux composed of resin, neutral chloride of zinc, and grease. The metal should not be cleaned or scraped unless it is absolutely necessary to do so, in which ease alcohol or essence of turpentine should be used for the purpose. For 5 per cent. aluminum bronze tin solder may be employed, but this is not possible with the 10 per cent. alloy, in which case the company recommends a preliminary copper plating. If it is difficult to dip the ends to be plated directly into the solution pieces of blotting paper soaked in a solution of CuS04 may be laid on them and a current passed. The flux mentioned above may be used.
Another solder which is recommended is one consisting of: Copper, 56 parts; zinc, 46 parts, and tin, 2 parts, applied with borax. In a test plates of aluminum soldered together, edge to edge, with these solubles required a tractive effort of 16 1/2 to 18 tons per square inch to pull them asunder; if the edges overlapped, 22 1/4 tons per square inch were required. Pieces of cast aluminum bronze, if placed in sand molds, can be joined together autogenously by running in some of the molten metal. If this operation is properly carried out the joint is indistinguishable from the rest of the casting. Thin cylinders of aluminum are made in this way by bending the sheets round end to end, and soldering with molten aluminum.
A solder for aluminum consists in combining cadmium, zinc and tin mixed in substantially the following proportions: Cadmium, 50 parts; zinc, 20 parts; tin, the remainder. The zinc is first melted in any suitable vessel, when the cadmium is added and then the tin in pieces. The mass must be well heated, stirred, and then poured. The soldering metal can be used for a variety of different metals, but is specially adapted to aluminum.