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19 December 2003

How to Solder Aluminum

Adapted from A Thousand and One Formulas 1920 by Sidney Gernsback.

There are various compounds on the mar-ket for soldering aluminum, but this operation depends more on the workman than on the solder and unless considerable experience has been had it is probably better to purchase solder than to attempt making it. Zinc can be used but does not form a very strong joint. Tin can also be used, is more nearly the color of aluminum, is stronger than zinc, but is very difficult to work. A small proportion of phosphor tin added to pure tin makes it work more readily and is the basis of most aluminum solder.

The chief difficulty in soldering alumi-num is that the heat is dissipated so rapidly that it cools the soldering iron and furthermore aluminum oxidizes instantly upon exposure to the air. This extremely thin film effectually prevents a perfect union being made. If the parts are well heated and melted solder kept hot while the iron is allowed to stand on it, the surface can be scraped beneath the melted solder by the point of the soldering iron, thus pre-venting to a certain extent the oxidization. In this way the metal can be tinned. When both parts to be brought together are well tinned, the parts can be united with some chance of success, nitrat of silver, resin, or zinc chloride being used as a flux. A soldering tool of nickel gives more satisfactory results than a copper one as the latter alloys with the tin and soon becomes rough.

Cleaning the Metal: If the surface is of such a shape that it cannot be readily cleaned by scraping, it can be cleaned by dipping it into a solution of nitric acid in three times its bulk of hot water contain-ing about 5 per cent of commercial hydrofluoric acid. This causes a slight action on the surface of the metal as shown by bubbles. Rinse the metal after removing from the acid bath and dry in hot sawdust.

Aluminum Solder

The following formula, in the hands of a competent man, can be used to unite aluminum or aluminoid parts:

Tin: 10 parts.
Cadmium: 10 parts.
Zinc: 10 parts.
Lead: I part.

These parts to be united must be thor-oughly cleansed and allowed to stand two to three hours in a strong solution of Hypo-Sulphate of soda before being operated upon, or cleaned in the acid bath described above.

Solder for Aluminum

Consists of zinc, tin, aluminum phos-phorus. The first two containing the bulk of the alloy. This solder can be used either with the blow pipe or the iron. If the former is used a !ittle silver can be added to it without making it melt and giving it a better color. The surfaces to be soldered are first scraped clean then tinned with the solder itself, no flux being needed. Silver, 2%; Aluminum Phosphorus, 9%; Tin, 34%; Zinc, 50%.