Hardening of aluminum profiles to press on ASTM B 807

Under quenching aluminum alloys understand alloy heated to a suitable temperature for a sufficient time to complete the transition of one or more soluble components of the alloy into solid solution and then cooling the material sufficiently rapidly to hold these components in solid solution.

Quenching with a separate heating furnace

Classical hardening aluminum alloys It occurs by separately heating the product in an oven and then rapidly cooling it in a tank with water, as well as other cooling methods.  Tempering is included as a necessary operation when processing aluminum alloys in the T3 condition, T4, T6, T7, T8 and T9, depending on the subsequent regime of aging.

Incomplete quenching aluminum alloys

At the same time, in practice for a long time for some of the profiles of aluminum alloys hardened produce not a single heating, and heating treatment with hot articles, often with the pressing temperature directly at the exit of the press.

It should be noted, that national standards GOST this issue presents a very vague and ambiguous. Quenching hot deformation temperature called incomplete quenching and T5 denote. Under full hardening only understand tempering from the separate heating designation T6. About any possibility to reach a state of complete hardening without a separate heating furnace is not mentioned anywhere.

Without proper control of heating and cooling profiles of the press hardening can really be incomplete. Причинами неполной закалки могут быть:
недостаточно полное растворение упрочняющих компонентов сплава при нагреве заготовки и/или последующем деформационном разогреве металла в ходе прессования;
– insufficiently rapid cooling profiles after exiting the die and therefore premature precipitation hardening components of the solid solution.

Aluminum alloys for full hardening on press

Of all the standards only American Standard ASTM B 807 regulates the procedure hardening aluminum alloys directly on the press. At the same time it limits the possibility of quenching at the press rather narrow circle of alloys of the series 6xxx and 7xxx. It is understandable, because such heat treatment is possible only for those alloys, whose chemical composition makes it possible to make it virtually.

Aluminum alloy, which can be "officially" to harden the press, стандарт относит следующие:

  • 6005, 6005A, 6105;
  • 6061, 6262, 6351;
  • 6060, 6063, 6101, 6463;
  • 7004, 7005;
  • 7029, 7046, 7116, 7129, 7146.

For these alloys, in press hardening it is a cheaper alternative, instead of expensive quenching process with a separate heating furnace. Thus it is possible to achieve the status T3 aluminum alloys, T4, T6, T7, T8 and T9.

For these alloys, in a standard analogues GOST 4784-97 на деформируемые алюминиевые сплавы можно найти только следующие аналоги:

  • alloys 6060 and 6063 – сплав АД31;
  • alloy 6061 - abortion AD33.

Some of these "American" alloys are purely American and have no analogues, for example, in European Standard EN 573-3. It belongs, for example, to alloys 7004, 7046, 7146.

On the other hand, This list does not contain the "European" alloy 6082, analogue of our AD35, which in Europe is also quenched in a press. Judging from the contents of magnesium and silicon, and Mn, условия закалки для сплава АД35 (6082) близки к условиям закалки сплава 6351.

ASTM B 807

Standard ASTM B 807 требует при применении закалки алюминиевых профилей на прессе необходимо жестко контролировать три следующих технологических параметра:

1) температура заготовки при загрузке ее в пресс – различная для различных групп сплавов;

2) максимальный интервал времени между выходом профиля из матрицы и входом его в зону закалки: от 45 by 90 секунд в зависимости от толщины профиля;

3) минимальная скорость охлаждения профиля в зоне закалки до достижения им температуры 200 ºС:
– from 70 ° C / min for the alloy 6060;
– by 500 ° C / min for the alloy 6061 .

The temperature of the workpiece while loading it into a press

The temperature of the workpiece at the beginning of compression should not be below or above, than indicated in the table 1 for the alloy. It should be borne in mind, that the surface temperature of the preform or column can be significantly different from their central part temperature. It is necessary to have data on this visible under temperature and the resulting metallurgical structure, and strength properties. After exiting the billet heating furnace must be loaded into the press as soon as possible, podstuzhivaniya avoid it to a temperature below a minimum value, specified for this alloy in Table 1.

 Table 1 - The temperature of the workpiece for pressingtemperatura-nagreva

 The pause between the metal matrix and the release of quenching

 The maximum time interval between the output of the molded profile of the matrix and its entrance into the quench zone should not exceed the value, indicated in table 2. The maximum permissible time between the release of the metal matrix and its entry into the quench zone is usually determined by the thinnest portion of the profile.

This condition depends on the pressing speed, as well as the duration of idle press process at restart preform. As can be seen from the table 2, minimum pause between the output of the matrix metal and the beginning of the quenching is 45 seconds. This time is quite enough to restart the workpiece in the press and passing 1-1,5 meters from the matrix to the entrance of the cooling unit on the press.

Table 2 - Permissible interval between the metal matrix and the release of
beginning its hardeningpauza-pered-zakalkoy

Minimum permissible quenching rate

Quenching profile must achieve a temperature below the 200 ° C within a specified short period of time, which depends on the quantity of alloy. This requirement depends on the cooling rate of the quenching profile in the press zone.  The minimum cooling rate for various alloy groups should meet the table 3. In this case it should be excluded repeated thawing metal.

Table 3 - Minimum metal cooling rate in the quench zoneskorost-oxlazhdeniya

Adjustment of process parameters

The above requirements for temperature and time parameters can be narrowed in the above range in view of the specifics of production equipment, as well as the pressing conditions, for example, отношения прессования (вытяжки) и формы поперечного сечения профиля. These changes should have statistical evidence of strength and other properties of profiles.

Organization of control on the press hardening technology

Profiles can be considered hardened on the press, if this ensures proper control of process parameters needed, as well as their registration and storage.

Control of preform temperature prior to compression

control technologies should ensure the exclusion of metal overheating or damaging pollution furnace atmosphere. for instance, induction heating requires measurements of temperature gradients along the workpiece. When applying a direct gas heating is necessary to correctly position the thermocouple due to the potential inhomogeneity of the surface temperature.

Temperature monitoring should include, как минимум:
1) температуру заготовки в печи нагрева и
2) температуру заготовки на выходе из печи непосредственно перед загрузкой в пресс.

metal temperature control after the release from the press

After leaving the press the control measuring points of the temperature profile is, как минимум:
1) температура металла на входе в закалочное устройство;
2) температура металла на выходе из закалочного устройства.

Control of timing

Контролируют и регистрируют следующие временные параметры:
время от выхода заготовки из печи нагрева и началом прессования;
время между выходом металла из пресса и его входом в закалочное устройство;
– residence time profile in the quenching device.

cooling rate control

Применяют следующие методы охлаждения:

  • прохождение профиля через воду или смесь воды и гликоля в стоячей волне;
  • погружение профиля закалочный бак;
  • подачу на профиль воды из спрейеров;
  • подачу на профиль водовоздушной смеси;
  • подачу на профиль сжатого воздуха;
  • комбинация указанных выше методов;
  • other methods.

hardening alloys 6060 and 6061 (АД31 и АД33)

To understand the essence of quenching at the press it is useful to compare the conditions for alloys 6060 and 6061. aluminum alloy 6060 - analogue AD31 alloy with a minimum content therein magnesium and silicon, a raft 6061 - full analogue AD33 alloy. The figure schematically shows the differences required of cooling rates of these alloys for quenching, i.e. creation of a solid solution of magnesium and silicon falling by preventing particles Mg2Si.

Recommended methods for cooling and the minimum cooling rate are indicated in Table 4. As seen, for profiles of alloy 6060 (АД31) с тонкими стенками, for example, most construction system profiles, enough cooling fans on the output table press. For profiles of alloy 6061 until thick 10 mm is sufficient cooling the water-air mixture, and it must have spreyernoe water cooling for profiles with a greater thickness.

 sxema-zakalki-6060-6061Figure - Scheme different cooling modes and the highlight area coarse Mg2Si alloys 6060 and 6061

Table 4 - Recommended quenching rate and cooling methods
hardening alloys on the press 6060 and 6061zakalka-6060-6061