Some aluminum alloys remain unstable for such long

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Some aluminum alloys remain unstable for such long periods after quenching that they are never used in the solution heat treated condition — for example, Unified Numbering System A97075 wrought aluminum alloy. If a solution heat treated alloy is precipitation hardened by heating at relatively low temperature, between 93 and 232 °C (200 and 450 °F), alloying atoms form small particles. At a critical size and distribution of particles, the strength of the aluminum alloy reaches a maximum. Conductivity increases during the precipitation hardening or artificial aging process. If aging is carried beyond the point where optimum strength is obtained, the strength will decrease but conductivity will continue to increase. Figure 12 shows the relationship between conductivity and strength for a typical structural aluminum alloy. Variations from specified heat treatment practice can result in aluminum alloys with strengths below required levels. Heat treatment discrepancies 332 Electromagnetic Testing T ABLE 1. Ranges of electrical conductivity for aluminum alloys. Alloy and Temper a Electric Conductivity _______________________________________________ _______________________________ Unified Numbering Aluminum Minimum Maximum __________________ __________________ System (UNS) Association (AA) MS·m –1 (%IACS b ) MS·m –1 (%IACS b ) UNS A91100 AA 1100 33.1 (57.0) 36.0 (62.0) UNS A92014, untempered AA 2014-0 28.1 (48.5) 29.9 (51.5) UNS A92014, temper 3XX AA 2014-T3XX 18.3 (31.5) 20.3 (35.0) UNS A92014, temper 4XX AA 2014-T4XX 18.3 (31.5) 20.3 (35.0) UNS A92014, temper 6XX AA 2014-T6XX 21.5 (37.0) 24.1 (41.5) UNS A92019, untempered AA 2219-0 24.9 (43.0) 26.7 (46.0) UNS A92019, temper 3XX AA 2219-T3XX 15.7 (27.0) 18.0 (31.0) UNS A92019, temper 62X AA 2219-T62X 18.0 (31.0) 20.6 (35.5) UNS A92019, temper 8XX AA 2219-T8XX 18.0 (31.0) 20.6 (35.5) UNS A92024, untempered AA 2024-0 26.4 (45.5) 29.0 (50.0) UNS A92024, temper 3XX AA 2024-T3XX 16.2 (28.0) 19.1 (33.0) UNS A92024, temper 4XX AA 2024-T4XX 16.5 (28.5) 18.9 (32.5) UNS A92024, temper 6XX AA 2024-T6XX 20.3 (35.0) 23.8 (41.0) UNS A92024, temper 8XX AA 2024-T8XX 20.9 (36.0) 24.7 (42.5) UNS A93003 AA 3003 25.8 (44.5) 29.0 (50.0) UNS A96061, untempered AA 6061-0 27.3 (47.0) 29.6 (51.0) UNS A96061, temper 4XX AA 6061-T4XX 20.6 (35.5) 24.1 (41.5) UNS A96061, temper 6XX AA 6061-T6XX 23.2 (40.0) 26.1 (45.0) UNS A97075, untempered AA 7075-0 25.5 (44.0) 27.8 (48.0) UNS A97075, temper 6XX AA 7075-T6XX 17.4 (30.0) 20.3 (35.0) UNS A97075, temper 73X AA 7075-T73X 22.0 (38.0) 24.7 (42.5) UNS A97075, temper 76X AA 7075-T76X 20.9 (36.0) 22.6 (39.0) UNS A97178, untempered AA 7178-0 24.9 (43.0) 27.3 (47.0) UNS A97178, temper 6XX AA 7178-T6XX 16.8 (29.0) 19.7 (34.0) UNS A97178, temper 76 AA 7178-T76 20.3 (35.0) 22.6 (39.0) a. X s represent numerals unspecified in this list. b. Percentage of International Annealed Copper Standard.
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include deviations or misapplication of the following processes: (1) solution heat treatment temperature, (2) solution heat treatment time, (3) quenching practice, (4) aging temperature, (5) aging time, (6) annealing temperature and time and (7) uncontrolled temperature application. Solution heat treatment temperatures for each aluminum alloy vary over a range. Wider ranges can lead to greater variations in conductivity and mechanical properties. For instance, Unified Numbering System 97075 wrought aluminum alloy can be solution heat treated at temperatures from 460 to 500 °C (860 to 930 °F) depending on product form and size. Solution heat treatment at the higher temperatures results in greater numbers of atoms in solution and in vacancies. These conditions provide slight increases in hardness and decreases in conductivity after quenching. Solution heat treatment at the lower end of the
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  • Fall '19
  • Magnetism, Magnetic Field, Electrical conductivity

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