Since the discovery of aluminium and its production in considerable quantities, it has become a common material in the manufacture of various artistic objects. One of the greatest difficulties, however, in the past has been that there was no perfect solder for aluminium, and various alloys were used which gave unsatisfactory results. This difficulty has now been overcome, and it is possible to solder the metal so perfectly that in tests which have been made the metal itself broke before the solder gave way.

The French manufacturers use five kinds of solder for aluminium, all consisting of zinc, copper, and aluminium, in different proportions. These are given below. Parts by weight.

I.

Zinc.......................................... 80

Copper........................................ 8

Aluminium.................................... 12

II.

Zinc .......................................... 85

Copper ....................................... 6

Aluminium .................................... 9

III.

Zinc ......................................... 88

Copper ........................................ 5

Aluminium .................................... 7

IV.

Zinc .......................................... 90

Copper ........................................ 4

Aluminium .................................... 6

V.

Zinc .......................................... 94

Copper ....................................... 2

Aluminium .................................... 4

There are also other compositions besides these. Bourbouze recommends, for objects which are to be further manipulated or worked on after soldering, a mixture of 45 parts of tin and 10 of aluminium.

Frischmuth gives the following alloys for solders:

The composition B (an ordinary soft solder) is adapted for soldering aluminium by means of the common soldering iron.

In preparing aluminium solders, the alloy of copper and aluminium is always made first, and the zinc added. First of all the copper is melted, and the aluminium put in gradually, usually in three or four portions. The two metals are of very different density, and the mixture should be stirred with an iron rod, to unite them as far as possible. Immediately after adding the last portion of the aluminium, the zinc is put in, and at the same time some fat or resin is thrown into the kettle, the whole is quickly stirred, the kettle removed from the fire, and the alloy poured into iron molds which have been rubbed with coal oil or benzine. The whole work must be done as quickly as possible after the addition of the zinc, or the solder will not remain in a suitable condition.

The zinc used should contain no iron, as a very small amount of the latter would materially affect the fusibility and durability of the solder. The purpose of the fat or resin is to prevent the oxidation of the zinc, and, as before observed, the work must proceed as rapidly as possible from this moment, as the temperature of the mass is so high that if it were left long in fusion much of the zinc would evaporate.

On account of its resistance to chemical influences, aluminium solder is frequently used by dentists to unite the metallic parts of artificial teeth, but alloys for this purpose must not contain copper except in very small quantities, as this metal is easily attacked by acids.

Platinum And Aluminium Solder

Gold ........................................ 30

Platinum.................................... 1

Silver ....................................... 20

Aluminium ................................... 100

Aluminium And Gold Solder

Gold........................................ 50

Silver....................................... 10

Copper ...................................... 10

Aluminium .................................. 20

Solder For Aluminium Bronze

Aluminium and copper make a very beautiful alloy, and one of valuable properties, much used for soldering artistic objects. Aluminium bronze demands a special composition, and for this purpose a common soft (white) solder is generally used, mixed with zinc amalgam in different proportions, either 2, 4, or 8 parts of the solder to 1 of the amalgam. Zinc amalgam is an alloy of zinc and mercury, as evident from its name (amalgam) being the general designation for alloys of mercury with other metals. To prepare it 2 parts of zinc and 1 of mercury are united, with heat. The zinc is melted, the mercury quickly stirred in and the mixture quickly cooled. It is a somewhat brittle alloy, silver white in color. To make the solder for aluminium bronze, the soft solder is melted, the zinc amalgam, finely powdered, added, and the mass at once pound out into molds.

The soldering must be done with a soldering tool made of pure aluminium; the solder would easily enough adhere, to be sure, to other metals, but would alloy itself with them, and its composition would be changed.

In using the five aluminium solders given above, the kind of soldering to be done must be taken into consideration; for small ornamental objects, for instance, No. 1 may be used; for larger articles, such as teapots, coffee pots, etc., No. 4 is most frequently employed.

Originally the solders composed of aluminium and zinc were the only ones used for aluminium articles; large objects were first put together with an easily fusible solder, and the soldering finished with a harder one. The alloys of aluminium and zinc have the disadvantage that they oxidize easily in melting, and the work is made much more difficult thereby. This can be remedied by dipping the fine grains of the solder (in which form it is used) in copaiva balsam, which acts as a reducing agent, besides excluding the air. But this is not necessary if the compositions containing copper are employed.