ASTM B661-12(2020)

Standard Practice for Heat Treatment of Magnesium Alloys

ABSTRACT
This practice is intended as an aid for establishing a suitable procedure for the heat treatment of magnesium alloys to achieve the proper physical and mechanical properties. Air chamber furnaces that may be either electrically heated, or oil- or gas-fired, are usually used for the heat treatment process. Each furnace must be gas tight, have suitable equipment for protective atmosphere, be equipped with a high-velocity fan or any other comparable means for circulating the atmosphere, and designed so that no direct radiation from the heating elements or impingement of the flame on the magnesium. It is also important that the furnace be calibrated before it is used initially and after any change in the furnace. Likewise, temperature-measurement systems should be regularly checked for accuracy.
SCOPE
1.1 This practice is intended as an aid in establishing a suitable procedure for the heat treatment of magnesium alloys to assure proper physical and mechanical properties.  
1.2 Times and temperatures are typical for various forms, sizes, and manufacturing methods and may not exactly describe the optimum heat treatment for a specific item. Consequently, it is not intended that this practice be used as a substitute for a detailed production process or procedure.  
1.3 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 77.120.20 - Magnesium and magnesium alloys
• Technical Committee: B07 - Light Metals and Alloys
• Drafting Committee: B07.04 - Magnesium Alloy Cast and Wrought Products

Relations

• Refers: ASTM B557-14 - Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products
• Effective Date: 15-May-2014
• Refers: ASTM B557-10 - Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products
• Effective Date: 01-Jul-2010
• Refers: ASTM E21-09 - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 01-Apr-2009
• Refers: ASTM B557-06 - Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products
• Effective Date: 01-May-2006
• Refers: ASTM E21-05 - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 01-Jun-2005
• Refers: ASTM E21-03a - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 01-Dec-2003
• Refers: ASTM E21-03 - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 10-Aug-2003
• Refers: ASTM B557-02a - Standard Test Methods of Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products
• Effective Date: 10-Oct-2002
• Refers: ASTM B557-02 - Standard Test Methods of Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products
• Effective Date: 10-Apr-2002
• Refers: ASTM E21-92(1998)e1 - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 18-Aug-1992
• Refers: ASTM E21-92(1998) - Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
• Effective Date: 18-Aug-1992

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B661 − 12 (Reapproved 2020)
Standard Practice for
Heat Treatment of Magnesium Alloys
This standard is issued under the fixed designation B661; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope aging and age softening, it is the result of precipitation from a
solid solution of one or more compounds whose solubility
1.1 This practice is intended as an aid in establishing a
decreases with decreasing temperature; for each alloy suscep-
suitable procedure for the heat treatment of magnesium alloys
tible to aging, there is a unique range of time-temperature
to assure proper physical and mechanical properties.
combinations to which it will respond.
1.2 Times and temperatures are typical for various forms,
3.1.2 heat treatment—a combination of heating and cooling
sizes, and manufacturing methods and may not exactly de-
operationsappliedtoametaloralloyinthesolidstatetoobtain
scribe the optimum heat treatment for a specific item.
desiredconditionsofproperties;heatingforthesolepurposeof
Consequently, it is not intended that this practice be used as a
hot working is excluded from the meaning of this definition.
substitute for a detailed production process or procedure.
3.1.3 quenching—rapid cooling; when applicable, the fol-
1.3 This standard does not purport to address all of the
lowing more specific terms should be used: still air quenching,
safety concerns, if any, associated with its use. It is the
forced air quenching, hot water/polymer quenching.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.1.4 solution heat treatment—a treatment in which an alloy
mine the applicability of regulatory limitations prior to use.
is heated to a suitable temperature and held at this temperature
1.4 This international standard was developed in accor-
for a sufficient length of time to allow a desired constituent to
dance with internationally recognized principles on standard-
enter into solid solution, followed by rapid cooling to hold the
ization established in the Decision on Principles for the
constituent in solution; the material is then in a supersaturated,
Development of International Standards, Guides and Recom-
unstable state, and may subsequently exhibit Age Hardening.
mendations issued by the World Trade Organization Technical
3.1.5 T4—solution heat-treated and naturally aged to a
Barriers to Trade (TBT) Committee.
substantially stable condition.
2. Referenced Documents
3.1.6 T5—artificially aged only; applied to products which
2.1 ASTM Standards: are artificially aged after an elevated-temperature rapid-cool
fabrication process, such as casting or extrusion, to improve
B557 Test Methods for Tension Testing Wrought and Cast
Aluminum- and Magnesium-Alloy Products mechanical properties or dimensional stability, or both.
E21 TestMethodsforElevatedTemperatureTensionTestsof
3.1.7 T6—solution heat-treated and then artificially aged;
Metallic Materials
applies to products which are not cold worked after solution
heat-treatment.
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
4. Apparatus
3.1.1 aging—describes a time-temperature-dependent
4.1 Furnaces used for the heat treatment of magnesium are
change in the properties of certain alloys; except for strain
usually of the air chamber type and may be electrically heated
or oil- or gas-fired. Because of the atmospheres used for
This practice is under the jurisdiction of ASTM Committee B07 on Light
solution heat treatment, furnaces must be gas tight and contain
Metals and Alloys and is the direct responsibility of Subcommittee B07.04 on
suitable equipment for the introduction of protective
Magnesium Alloy Cast and Wrought Products.
atmospheres, and means for control of those atmospheres. In
Current edition approved Nov. 1, 2020. Published December 2020. Originally
ordertopromoteuniformityoftemperature,furnacesshouldbe
approved in 1979. Last previous edition approved in 2012 as B661 – 12. DOI:
10.1520/B0661-12R20.
equipped with a high-velocity fan or comparable means for
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
circulating the atmosphere. In the design of the furnace it is
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
desirable that there be no direct radiation from the heating
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. elements or impingement of the flame on the magnesium.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B661 − 12 (2020)
4.2 Automatic recording and control equipment to control thermocouples located at front, center, and rear, or at top,
the temperature of the furnaces, which must be capable of center, and bottom of the furnace.
maintaining temperature in the working zone to within 610 °F
5.1.2.5 Perform the surveys in such manner as to reflect the
(66 °C) of the specified temperature.
normaloperatingcharacteristicsofthefurnace.Ifthefurnaceis
normally charged after being stabilized at the correct operating
4.3 There must be a separate manual reset safety cutout
temperature, similarly charge the temperature-sensing ele-
which will turn off the heat source in the event of any
ments. If the furnace is normally charged cold, charge the
malfunctioning or failure of the regular control equipment.
temperature-sensing elements cold. After insertion of the
Thesesafetycutoutsshallbesetascloselyaspracticableabove
temperature-sensing elements, readings should be taken fre-
the maximum temperature for the alloy being heat treated.This
quently enough to determine when the temperature of the
willbeabovethevariationexpected,butshallnotbemorethan
hottest region of the furnace approaches the bottom of the
10 °F (6 °C) above the maximum solution heat treating tem-
temperaturerangebeingsurveyed.Fromthattimeuntilthermal
perature for the alloy being heat treated. Protective devices
equilibrium is reached, the temperature of all test locations
shall also be installed to turn off the heat source in case of
should be determined at 2-min intervals in order to detect any
stoppage of circulation of air, and they shall be interconnected
overshooting. After thermal equilibrium is reached, readings
with a manual reset control.
should be taken at 5-min intervals for sufficient time to
4.4 The furnaces or ovens used for aging treatments may be
determine the recurrent temperature pattern, but for not less
heated by means of electricity, gas, or oil. The temperature at
than30min.Beforethermalequilibriumisreached,noneofthe
any point in the working zone, for any charge, shall be
temperature readings should exceed the maximum temperature
maintained within 610 °F (66 °C) of the desired aging tem-
of the range being surveyed. After thermal equilibrium is
perature after the furnace has been brought up to the aging
reached, the maximum temperature variation of all elements
temperature.
(both load and furnace thermocouples) shall not exceed 20 °F
4.5 Quenching:
(11 °C) and shall not vary outside the range being surveyed.
4.5.1 Normally magnesium work loads are cooled in air.
5.1.2.6 For furnaces used only for treatments other than
This should be by fan cooling the furnace charge after removal
solution heat treatment, after the initial temperature uniformity
from the furnace in such a way that the cooling is uniform on
survey as outlined in 5.1.2.5, surveys need not be made more
various parts of the furnace charge.
often than at each six-month interval, provided that (a) test
4.5.2 Some alloys (notably EV31A, EQ21A, and QE22A)
specimens from each lot are tested and meet applicable
arequenchedinwaterorothersuitablemediafromthesolution
material specifications requirements, (b) the furnace is
heat treating temperature. Quench facilities should be situated
equipped with a multipoint recorder, or (c) one or more
near the heat treatment furnaces. If required, means of heating
separate load thermocouples are employed to measure and
the quench medium should be provided. Handling equipment
record actual metal temperatures.
shall be such that it is possible to quench heat treatment loads
5.1.2.7 Monthly surveys for batch furnaces are not neces-
within 30 s after the opening of the furnace door.
sary when the furnace is equipped with a permanent multipoint
recording system with at least two sensing thermocouples in
5. Calibration and Standardization
each working zone, or when one or more separate load
thermocouples are employed to measure actual metal
5.1 Calibration of Equipment:
temperature, providing that uniformity surveys show a history
5.1.1 Surveys:
of satisfactory performance for a period of at least six months.
5.1.1.1 Perform a temperature survey, to ensure compliance
Thesensingthermocouplesshallbeinstalledsoastorecordthe
with the applicable recommendations presented herein for each
temperature of the heated air or actual metal temperatures.
furnace.
However, periodic surveys shall also be made at six-month
5.1.1.2 Make a new temperature survey after any changes
intervals in accordance with the procedures outlined for the
in the furnace that may affect operational characteristics.
monthly survey.
5.1.2 Furnace Calibration:
5.1.2.8 Do not use furnace control temperature-measuring
5.1.2.1 Make the initial temperature survey at the maxi-
instruments to read the temperature of the test temperature-
mum and minimum temperature of solution heat treatments
sensing elements.
and aging heat treatment for which each furnace is to be used.
3 3
There shall be at least one test location for each 25 ft (0.7 m )
5.1.3 Temperature-measuring System Check—Check the ac-
of air furnace volume up to a maximum of 40 test locations
curacy of temperature-measuring system under operating con-
with a minimum of nine test locations.
ditions weekly. Check should be made by inserting a calibrated
5.1.2.2 After the initial survey, survey each furnace
test temperature-sensing element adjacent to the furnace
monthly, except as provided in 5.1.2.7. The monthly survey
temperature-sensing element and reading the test temperature-
shall be at one operating temperature for solution heat treat-
sensing element with a calibrated test potentiometer. When the
ment and one for aging heat treatment.
furnace is equipped with dual potentiometer measuring
5.1.2.3 For the monthly surveys there shall be at least one
systems, which are checked daily against each other, the above
3 3
test location for each 40 ft (1.13 m ) load volume. checks may be conducted every three months rather than every
3 3
5.1.2.4 For furnaces of 10 ft (0.28 m ) or less the week. Calibrate the test temperature-sensing element,
temperature survey may be made with a minimum of three potentiometer, and cold junction compensation combination
B661 − 12 (2020)
A
TABLE 1 Recommended Heat Treatment Schedules for Magnesium Alloy Castings (for Castings of Up to 2 in. (50.8 mm) in Section)
B C
Alloy Aging Treatment Solution Heat Treatment Aging after Solution
Maximum
Final Temperature, Temperature, Temperature,
ASTM UNS Time, h Time, h Temperature, Time, h
E E
Temper ±10 °F (±6 °C) ±10 °F (±6 °C) ±10 °F (±6 °C)
°F (°C)
D
A—Mg-Al-Zn Group
AM100A M10100 T5 450 (232) 5 795 (424) 16 to 24 810 (432)
T4 a. 775 (413) 6
b. 665 (352) 6
c. 775 (413) 10
T6 450 (232) 5
T61 425 (218) 25
AZ63A M11630 T5 500 (260) or 4
450 (232) 5
T4 725 (385) 10 to 14 735 (391)
T6 425 (218) 5
450 (232) 5
AZ81A M11810 T4 775 (413) 16 to 24 785 (418)
F
a. 775 (413) 6
b. 665 (352) 2
c. 775 (413) 10
F G
AZ91C M11914 T5 335 (169) or 16
420 (215) 4
T4 775 (413) 16 to 24 785 (418)
F
a. 775 (413) 6
b. 665 (352) 2
c. 775 (413) 10
F G
T6 335 (168) 16
420 (216) 5to6
AZ91E M11919 T6 . . 775 (413) 16 to 24 785 (418) 335 (168) 16
420 (216) 5to6
F
a. 775 (413) 6
b. 665 (352) 2
c. 775 (413) 10
F G
AZ92A M11920 T5 500 (260) 4
T4 765 (407) 16 to 24 775 (413)
T6 425 (218) 5
F
d. 765 (407) 6
e. 665 (352) 2
f. 765 (407) 10
F G
G
ZC63A M16331 T6 . . 825 (440) 8 840 (449) 370 (188) 16 to 24
B—Mg-Zr Group
B C
Aging Treatment Solution Heat Treatment Aging after T4
Temperature, Maximum
Temperature, Temperature,
E
Time, h ±10 °F (±6 °C) Time, h Temperature, Time, h
E E
±10 °F (±6 °C) ±10 °F (±6 °C)
°F (°C)
G
EQ21A M12210 T6 . . 970 (521) 4 to 8 980 (527) 400 (204) 8 to 16
G
EV31A M12310 T6 . . 970 (521) 6 to 8 980 (527) 400 (204) 10 to 16
EZ33A M12330 T5 420 (216) or 5
H
650 (343) 2
G
QE22A M18220 T6 980 (527) 4 to 8 1000 (538) 400 (204) 8 to 16
WE43A M18430 T6 975 (525) 4 to 8 990 (530) 480 (250) 16
WE43B M18432 T6 975 (525) 4 to 8 990 (530) 480 (250) 16
WE54A M18410 T6 975 (525) 4 to 8 990 (530) 480 (250) 16
I
ZE41A M16410 T5 625 (329) plus 2
I
350 (177)
ZK51A M16510 T5 350 (177) or 12
424 (218) 8
D
ZK61A M16610 T5 300 (149) 48
T6 930 (499) or 2 940 (505) 265 (129) 48
900 (482) 10
A
Heavy sections may require a longer time than indicated in this table.
B
Castings to T5 temper are aged from “as-cast” condition.
C
After solution heat treatment, and before aging, castings are cooled to room temperature by fast fan cooling, except where indicated differently.
B661 − 12 (2020)
D
Thealloysshowninthistablesection(Mg-Al-ZnGroupandZK61A)areloadedintothefurnaceat500 °F(260 °C)andbroughttoholdingovera2-hperiodatauniform
rate of temperature rise. This does not apply to ZC63A which has zinc and copper.
E
Except where quoted differently.
F
Analternativeheattreatment,ifrequiredtominimizegraingrowth,consistsofasequentialtreatmentasindicatedforalloysAM100A,AZ81A,AZ91C,AZ91E,andAZ92A.
G
Quench from solution heat treatment temperature either in water heated to 150 °F (66 °C) or in other suitable quench media.
H
This alternative aging treatment for EZ33A alloy can be used where maximum resistance to creep at elevated temperature is not of prime importance.
I
The2hat625°F(329°C)isadequatetoobtainsatisfactoryproperties.The16hat350 °F(177 °C)isoptionaltogiveaveryslightimprovementinmechanicalproperties.
againstNationalInstituteofStandardsandTechnologyprimary 5.3.1 Test specimens prepared in accordance with 5.2.1 and
orsecondarycertifiedtemperature-
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