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- Publisher
- Emerald Publishing
- Copyright
- Copyright © Emerald Group Publishing Limited
- ISSN
- 0002-2667
- DOI
- 10.1108/eb031728
- Publisher site
- See Article on Publisher Site
Abstract
FABRICATION The Electric Welding of TABL E 1.—ELECTRODE GAUGES , CURREN T STRENGTHS , AN D PLATE GAPS Aluminium and its Alloys Thickness Gauge of Current Range Plate Gap of Material Electrode in Amps Recommended 12 40— 45 Close butt A Note on Some of the Problems that Arise and also 1/15 in. 1/33 in. 10 80— 95 ,, ,, J in. 8 95—105 Some of the Pitfalls to be Avoided 3/16 in. 6 130—150 1/15 in. ¼i in . •4 190—210 * in. 4 200—225 ¾ in . -ft in. or bevelled 70 deg. wit h 1/15 in . step By G. FitzGerald-Lee, F.R.S.A., M.I.E.I., A.R.Ae.S. dispensed with if aero-engine castings are welded EW processes have made such an advance available which are particularly suited to welding. immediately after removal from a trichlorethylene during the last two years as has the are weld One of the best known of these is Hiduminium degreasing bath at 80 deg. C. On the other hand, ing of aluminium and its alloys. In the 1945 33, a corrosion resisting medium strength wrought localized are welding is frequently successful impression of the Second Edition of his Engineer alloy containing up to 4 per cent magnesium, 1 without preheating, providing high currents are ing Materials, Machine Tools and Processes per cent manganese, 0·75 per cent iron, 0·6 per used for the early runs; typical values are 130, (Longmans), W. Steeds states, on page 148: cent silicon, 0·5 per cent chromium, and 0·15 per 170, and 200 amps for Nos. 10, 8, and 6 gauge 'It is impossible to weld aluminium by the cent copper. It is particularly suitable for welding electrodes respectively. As would be expected, are process using bare electrodes, but with owing to the sound joins obtainable, combined the amount of spatter is increased when such covered ones it is possible, though somewhat with a high residual strength in the weld zone. high current values are used, and normal currents difficult; the electrode is made positive and Other Hiduminium wrought alloys suitable for should be used as soon as the flow of weld metal should be held nearly vertical. Spot welding is welding are 11, 22, and 44, all being corrosion permits. Direct current should be used for weld quite satisfactory on aluminium but very high resisting low strength wrought alloys. ing, with the electrode connected to the positive currents and very short welding times are The Noral alloy most suitable for welding is terminal of the generator. Tacks should be spaced necessary. 33S, with 5 per cent silicon; it possesses very good at not more than 6 in. intervals. The electrodes That paragraph, quite true at the time it was formability and corrosion resistance, but only should be held vertically, with as close an are as written, is not true today; the are welding of fair machinability. Other Noral wrought alloys possible, and the current strength should be aluminium is now no more 'difficult' than the suitable for welding are 2S (almost pure alumi adjusted carefully to suit the particular thickness nium), 3S, and M57S. oxy-acetylene welding of the same metal, but in of material. The rate of deposition of the electrode each case there is a correct technique to be Cast aluminium alloys which are particularly is very much higher than is used with steel. acquired if successful welds are to be the result. suitable for welding are Noral 125 and 160. The sequence of welding should be designed The technique of welding aluminium by the Noral 125, containing 5 per cent silicon, 1·25 per to reduce the risk of distortion, and in general electric are process differs from that used in the cent copper, and 0·5 per cent magnesium, can, as should be carried out toward the free end, par welding of mild steel, and the principal advantages with all Noral casting alloys, be sand or chill cast, ticularly in such rigid articles as castings. Instead of the metallic are process for welding aluminium and its corrosion resistance and machinability of attempting to weld up cracks in lugs or bosses, are greater speed of welding and reduced dis are good. Noral 160 contains 12 per cent silicon, it is advisable to cut part of the casting away and tortion of the metal. rendering its machinability poor but its corrosion to build up a solid boss which is redrilled. Owing resistance very good. Other Noral casting alloys Many of the difficulties encountered in welding to the interaction of dissimilar alloys, a slight aluminium are due to the inherent properties of suitable for welding are 123, 161, and 162 (or amount of porosity is sometimes found at the the metal. Owing to its higher specific and latent 'Lo-Ex'). weld junction on castings and, where a sound heats, it requires as much heat input per pound More care is necessary in the preparation of surface is required after machining, the fault in to melt as mild steel, although its melting point is welds on aluminium than for many other metals, the casting should be chipped out to ensure the about 800 deg. C lower. The loss of heat by con and it has been found that one of the causes of junction being below the level of the finished duction during welding is also far greater than porosity in welds is the presence of a film of surface. Porosity is also liable to occur on super occurs in steel, and these considerations explain moisture on the surface of the metal to be welded. imposed runs if the slag is not completely cleaned why it is frequently necessary to preheat large This can be removed by heating to about 200 deg. objects of aluminium before welding. Aluminium C. before welding or by scratch-brushing. (Concluded on previous page) and its alloys form on their surfaces an adherent The presence of grease on the surface to be oxide film, which prevents the running together welded is objectionable, and any dirt or oil of globules of molten metal unless a powerful should be completely removed. Owing to the flux is used during welding. fluid character of aluminium and its alloys it is frequently necessary to use a grooved backing It has been found that the corrosion resistance of aluminium is adversely affected by impurities, strip to prevent the weld metal from running especially silicon and iron. For these reasons through. This backing material may be steel, pure sheet aluminium is still used in the manu copper, or asbestos. For the same reason, are welding of aluminium is largely confined to down- facture of vessels for the processing of food and hand welding. Fillet welds are not recommended chemicals in spite of the development of numerous for this process as they are liable to cause an aluminium alloys. The welding of some of these entrapment of flux between the edges of the plate. alloys presents obstacles due to their dependence This flux in the presence of a humid atmosphere for their final properties upon heat-treatment and, is liable to cause pronounced corrosion of the in many cases, upon the effect of forging for pro ducing refinement of the crystal structure and joint and there is no adequate means of cleaning even distribution of the constitutents. On the the joint before service. In welding sections of different thicknesses, there is a tendency for the other hand, many of the non-heat-treatable alloys thinner material to melt away too rapidly unless used in the form of castings such as crankcases, the edge of the thicker section is gradually radiators or other parts in the automobile and reduced in thickness. aircraft industries can be welded satisfactorily. These cast parts, however, are rarely fabricated In repair work on castings the crack is usually from separate castings, and welding on them is bevelled to give an included angle of 60 deg.-90 usually undertaken to repair breakages. deg., an d it is advisable to 'locate' the crack (drill a hole about ⅛ in. diameter just beyond the end of To cover these applications, two main types of the fracture) to prevent its extending any farther. electrode are available; aluminium-silicon and Occasionally it is advantageous to replace a pure aluminium. The aluminium-silicon type deposits an alloy containing about 5 per cent number of small fractured pieces with a patch of silicon; it is ideally suited to the repair of castings, wrought material. even though the casting may not be of the As a general rule, heavy wrought material aluminium-silicon type. The core wire in the pure should be preheated to 150 ± 50 deg. C , and aluminium electrode consists of 99·5 per cent castings to 200 ± 100 deg. C , depending on the minimum purity aluminium, an d its main use is in complexity of the castings. The rate of heating the welding of pure aluminium vessels. must be low and uniform in order to avoid dis Several aluminium alloys are now commercially tortion and cracks. Additional preheating can be February 1949 55
Journal
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Feb 1, 1949