ASTM B918-17(R2017) pdf free download

ASTM B918-17(R2017) pdf free download.Standard Practice for Heat Treatment of Wrought Aluminum Alloys
1. Scope
1.1 This practice is intended for use in the heat treatment of wrought aluminum alloys for general purpose applications. 1.1.1 The heat treatment of wrought aluminum alloys used in specific aerospace applications is covered in AMS 2772. 1.1.2 Heat treatment of aluminum alloy castings for general purpose applications is covered in Practice B917/B917M. 1.2 Times and temperatures appearing in the heat-treatment tables are typical for various forms, sizes, and manufacturing methods and may not provide the optimum heat treatment for a specific item. 1.3 Some alloys in the 6xxx series may achieve the T4 temper by quenching from within the solution temperature range during or immediately following a hot working process, such as upon emerging from an extrusion die. Such alternatives to furnace heating and immersion quenching are indicated in Table 2, by Footnote L, for heat treatment of wrought alumi- num alloys. However, this practice does not cover the require- ments for a controlled extrusion press or hot rolling mill solution heat treatment. (Refer to Practice B807 for extrusion press solution heat treatment of aluminum alloys and to Practice B947 for hot rolling mill solution heat treatment of aluminum alloys.) 1.4 Units—The values stated in either SI units or inch- pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non- conformance with the standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. 1.6 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Equipment
4.1 Heating Media—Aluminum alloys are typically heat- treated in air chamber furnaces or molten salt baths; however, lead baths, oil baths, or fluidized beds, may be used. The use of uncontrolled heating is not permitted. Whichever heating means are employed, careful evaluation is required to ensure that the alloy being heat-treated responds properly to heat- treatment and is not damaged by overheating or by the heat-treatment environment. 4.1.1 Air chamber furnaces may be oil- or gas-fired or may be electrically heated. Furnace components that are signifi- cantly hotter than the metal should be suitably shielded for metal less than 0.250 in. [6.35 mm] thick to prevent adverse radiation effects. The atmosphere in air chamber furnaces must be controlled to prevent potential porosity resulting from solution heat treatment (see Note 1). The suitability of the atmosphere in an air-chamber furnace can be demonstrated by testing, in accordance with 7.4.2.1, that products processed in that furnace are free from heat-treat induced porosity. N OTE 1—Heat-treat induced porosity may lower mechanical properties and commonly causes blistering of the surface of the material. The condition is most likely to occur in furnaces in which the products of combustion contact the work, particularly if the gases are high in water vapor or contain compounds of sulfur. In general, the high-strength wrought alloys of the 2xxx and 7xxx series are most susceptible. Low-strength and Alclad (two sides) products are practically immune to this type of damage. Anodic films and proprietary heat-treat coatings are also useful in protecting against porosity resulting from solution heat treatment. Surface discoloration is a normal result of solution heat treatment of aluminum alloys and should not be interpreted as evidence of damage from overheating or as heat-treat induced porosity (see 7.4.2.1). 4.1.2 Salt baths heat the work rapidly and uniformly.