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Aviation History
1937
1937 - 1108.PDF
SUPPLEMENT TO FLIGHT 420^ 24 THE AIRCRAFT ENGINEER APRIL 29, 1937 Silicon*Aluminium Wire It has been found that the addition of silicon to alumin ium results in many useful features. Since silicon is a lighter element than aluminium the addition of silicon causes a decrease in the specific gravity, which is of extreme importance in those industries in which lightness is an essential feature. The addition of silicon to alumin ium causes the disappearance of hot-shortness, shrinkage is decreased and the melting-point of the metal is reduced. The effect of adding silicon to aluminium is to reduce the melting point of aluminium progressively until a minimum melting point of about 5750 C. is reached in the neighbour hood of 12 to 13 per cent, silicon. The tensile strength and the hardness of the material are increased by the addition of silicon. There are two general types of silicon-aluminium welding wire, the 5 per cent, silicon and the 10 per cent, silicon, and we may consider the properties of each in turn. 5 per cent. Silicon-Aluminium Alloy Welding Wire.— This is a drawn rod consisting of about 95 per cent, alumin ium and 5 per cent, silicon. There are also small amounts of iron, copper, zinc, etc. When deposited by the oxy-acetylene blowpipe flame the structure shown in the micrograph (Fig. 6) is obtained. The mechanical properties of the metal when deposited without any subsequent heat treatment are as follows : — Yield stress Ultimate stress Elongation Brinell hardness Izod impact value 3.7 Tons/sq. in. 7.4 Tons/sq. in. 7% in 2in. 37° 2.7 ft. lb. 10 per cent. Silicon-Aluminium Welding Wire.—This material contains about 10 to 12 per cent, silicon, and naturally it is considerably lighter than pure aluminium. Fig. 7.—Ten per cent, silicon aluminium. The use of this rod is almost entirely confined to castings, particularly those of the Alpax type. The rod has a melting point 60-70 deg. lower than that of pure aluminium. '£*+ *****.•* *r**lm. —V •*, :v.«rr^*?ii» '• ' •* 4* r#^* ^ J^L. %?/• * -v affi ,v/ Fig. 8.—Five per cent, copper aluminium. This rod is used for welding castings which have a composition that includes approximately five per cent, copper. The rod gives a deposit which is harder than that of the other aluminium alloy welding wires described. If the specific gravity of pure aluminium is taken as 2.70, that of the alloy would be only about 2.65. The melting point is considerably lower than pure aluminium, which is an extremely useful property in many cases. When deposited by the oxy-acetylene blowpipe the structure ol the material is as shown in Fig. 7. The mechanical properties of the deposited metal are as follows: — Yield stress . . Ultimate stress Elongation Brinell hardness Izod impact value 5.7 Tons/sq. in. 8.9 Tons/sq. in. 6% in 2in. 46.8 1.6 ft. lb. Copper-Aluminium Wire 5 per cent. Copper-Aluminium Alloy Welding Wire.— Copper-aluminium alloys have been used in industry for a long time for such purposes as domestic utensils, auto mobile parts, etc., and they have many desirable proper ties. They have good tensile strength, ductility and quite a low specific gravity. The rod suitable for the welding of copper and alumin ium alloys is known as the 5 per cent, copper-aluminium alloy. The rod consists of 95 per cent, aluminium and 5 per cent, copper and must not contain more than 0.5 per cent, of impurities. The structure of the deposited material is shown in the micrograph (Fig. 8), and such a deposit gave the following figures for the mechanical properties: — Yield stress . . . . 5.8 Tons/sq. in. Ultimate stress .. 6,2 Tons/sq. in. Elongation .. , . I y0 in 2in. Brinell hardness .. 80.0 Izod impact value .. 1.2 ft. lb.
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