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Solution Heat Treatment Metal
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Temperature The temperatures used for solution heat treating vary with different alloys and range from 825*F, to 980*F. As a rule, they must be controlled within a very narrow range (plus or minus 10*) to obtain specified properties. If the temperature is too low, maximum strength will not be obtained. When excessive temperatures are used, these is danger of melting the low- melting constituents, of some alloys with consequent lowering of the physical properties of the alloy. Even if melting does not occur, the use of higher-than-recommended temperatures promotes discoloration and increase quenching strains.
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Solution Heat Treatment Metal |
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Time of Temperature The time at temperature, referred to as soaking time, is measured from the time the coldest metal reaches the minimum limit of the desired temperature range. The soaking time varies, depending upon the alloy and thickness, from 10 minutes for thin sheets to approximately 12 hours for heavy forgings. For the heavy sections, the nominal soaking time is 1 hour for each inch of cross-sectional thickness. The soaking time is chosen so that it will be the minimum necessary to develop the required physical properties. The effect of an abbreviated soaking time is obvious. An excessive soaking period aggravates high-temperature oxidation. With clad material, prolonged heating results in excessive diffusion of copper and other soluble constituents into the protective cladding and may defeat the purpose of cladding. Quenching After the soluble constituents are in solid solution, the material is quenched to prevent or retard immediate re-precipitation. Three distinct quenching methods are employed. The one to be used in any particular instance depends upon the part, the alloy, and the properties desired. Cold Water Quenching. Parts produced from sheet, extrusions, tubing, small forgings, and similar type material are generally quenched in a cold water bath. The temperature of the water before quenching should not exceed 85*F. A sufficient quantity of water should be used to keep the temperature rise under 20*F. Such a drastic quench ensures maximum resistance to corrosion. This is particularly important when working with such alloys as 2017, 2024, and 7075. This is the reason a drastic quench is preferred, even though a slower quench may produce the required mechanical properties. Hot Water Quenching Large forgings and heavy sections can be quenched in hot or boiling water. This type of quench minimizes distortion and alleviates cracking which may be produced by the unequal temperatures obtained during the quench. The use of a hot water quench is permitted with these parts because the temperature of the quench water does not critically affect the resistance to corrosion of the forging alloys. In addition, the resistance to corrosion of heavy sections is not as critical a factor as for thin sections.
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