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Heat Treatment of Non-Ferrous Metals and Alloys

Method of Heating Metals such as Duralumin and aluminum are heat treated in a salt bath. This is a mild steel bath containing a mixture of potassium an sodium nitrates, which is heated by gas, oil and electricity. Heat Treatment of Duralumin Anealing: This operation permits the material to be worked and bent. Duralumin is annealed in a salt bath at a temperature between 360 degrees Celsius and 400 degrees Celsius and then quenched in clean cold water. Normalizing: Duralumin is normalized to relieve stresses and strains set up by working. Duralumin is normalized in a salt bath at a temperature between 485 degrees Celsius, and 505 degrees Celsius an then quenched in clean water. Note: Normalized Duralumin gradually becomes harder and stronger (age-hardens) during the three or four days after treatment. Heat Treatment of Aluminium Annealing is the only heat treatment applied to aluminum. Sheet which has been hardened by cold working can be restored to a soft ductile condition
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Anti-Corrosive Treatments

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Critical bodies such as aircraft structures are designed to provide maximum strength with minimum weight therefore unchecked corrosive attack would have serious consequences resulting in the failure of the structure. The following methods are employed to prevent corrosion. (a) By making the metal to form its own protective coating for example, anodizing aluminium and its alloys, chrornating magnesium and cosleitising steel. (b) Covering the surface with another metal less likely to corrode for example, galvanizing steel, hot-rolling aluminium (alclad), and metal spraying. (c) Covering the surface with a protective agent for example, enamel, paint, varnish, oil, grease or lanolin, depending on the material to be protected. Anti-corrosive treatment is given during manufacture to most parts of an airframe as a protection against corrosion and deterioration. The treatment of parts normally provides a very thin anti-corrosive film which is generally covered by a protective finish to
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Corrosion - Types and Recognition

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Corrosion is the conversion of metals to metallic oxides and salts which neither resemble nor possess the physical properties of the base metals. The conditions under which  corrosion may occur are many and varied, but it can be stated that the cause is due to electro-chemical action. Some metals have a greater tendency to corrode than others. The following  table shows various metals in their order of corrodibility.        Surface Corrosion  This is the most common form of corrosion, but is readily detected by the difference in  appearance between the products of corrosion and base metal. Corrosion on steel (commonly  known as rust) is reddish-brown in color; on aluminium‘ and its alloys it is a white or grey  powder and on copper a greenish discoloration. Surface corrosion is caused in a mild form by normal atmospheric conditions,  becoming more pronounced in a moist atmosphere, even more rapid with alternate moist and  dry conditions and greatly accelerated by high temper
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Practical Heat Treatment of Steel

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Method of Heating  Steel should be heated slowly and uniformly, as the temperature to which steel is  heated is one of the factors determining the success of any heat treatment. It is   to use heating equipment which permits rigid control of the temperature. Muffle furnaces ovens usually heated by oil. gas or electricity, are clean to use, capable of high degree of heat  and can be left at any given temperature Without fear of overheating. The use of the black  smith's fire is not a good method of heating, as temperature control and uniform   difficult to maintain. Unless great care is taken, the metal may become overheated and burnt. When using a blacksmith’s fire heat the jobs, if possible, in a steel tube and not directly in  the flame. Baths heated by oil or gas and containing low melting point alloys or molten salts  provide a good method of heat-treating steel. The heating is clean uniform and under strict  control. Irregular shapes can be heated throughout without overhea
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Changes of Carbon Steel Properties During Hardening, Tempering, Annealing, Normalizing and Refining

  Hardening 1. When carbon steel is heated to a temperature, a little above its upper critical point  and then cooled by drastic quenching, the normal structural change does not occur. The  rapid cooling arrests the formation of pearlite, and the austenite is changed into another micro-structure. "Martensite ” which is extremely hard and brittle. If the rate of ‘cooling  is not quite so drastic, then the austenite transforms into another structure called “ Troostite ”  which is less hard but very tough. An even lower rate of cooling will produce “ Sorbite,”  a finely grained structure which is strong and ductile. This hardening effect on carbon steel is  only slightly apparent upto 0.25% carbon content, appreciable above 0.6% carbon and almost  attains its full value in a 0.87% carbon steel. Thus the degree of hardness of steel is dependent upon its carbon content and the rate of cooling.  2. This hardening treatment gives the steel: (a) Small grain size. (b) Maximum hard
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Elementary Heat Treatments of Metals

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Introduction l. Plain carbon steel owes its properties to the presence of carbon. Steels which  owe their properties to elements other than carbon are termed alloy steels. The effects of  carbon when added to iron are best understood by first considering pure iron. Pure iron is very  ductile, and has a tensile strength of 18 tons per sq. in. The addition of carbon to the iron  increases the tensile strength, hardness and brittleness. and at the same time decreases the  ductility (0.87 per cent. carbon steel has a tensile strength of approximately 55 tons per sq.  in.). The increase in strength of steel with increase in carbon content is limited to the amount  of carbon which will remain combined with the iron after any normal heat treatment. Above  1.7 per cent. carbon, the excess carbon is in free state or graphite, which has Very low strength.  The carbon content of plain carbon steel rarely exceeds 1.5 per cent. 2. When steel is heated, the internal structure of  the steel
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How to Identify Metals

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1. Owing to the various grades of material in the same metallic group, metals are  not designated by name, but are marked to indicate clearly the specification with which  they comply. Identification markings are usually made with metal dies, but where such  a procedure may harm the material, stenciling or printing with paint enamel or ink is  employed. 2. Standard Color Code: The markings described above may not be easily observed,  so an additional method, known as the Standard Color Code, is employed to make  identification more obvious. The appropriate identification colors for each specification are  given in A.P. 1086 and in A.P. 1464 B. The colors are marked in bands across corners  of sheets and around the ends of tubes and rods. Should it be necessary to cut o material from a marked sheet, tube or rod, the cutting should be done in such a manner that the  identification colors remain on the material which is not required for use. 3. Practical Tests:  The approximate identifica
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