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Vacuum Hardening Sensitivity of Aluminum Alloy Profiles

Aluminum and aluminum alloy products account for more than 70% of extrusion products. The development of aluminum alloy profile extrusion technology has therefore led to the development of modern extrusion technology.Vacuum heat treatment of aluminum alloy profiles: through different vacuum hardening and aging systems, the aluminum profiles can get the proper mechanical properties.

The heating and holding time of vacuum hardening of aluminum extrusion profiles mainly depends on the solid solution velocity of the strengthening phase; and the solid solution velocity of the strengthening phase is related to the vacuum hardening heating temperature, the nature of the alloy, the microstructure, the size of the aluminum profile section, the heating conditions, the medium and It depends on factors such as how much furnace is loaded.

Generally, when the heating temperature of vacuum hardening is higher than the upper limit, the holding time is correspondingly shorter; after high temperature extrusion, the deformation degree is larger, the holding time is shorter; and the aluminum profile that has been vacuum annealed in advance, due to the slow precipitation of its strengthening phase, is relatively coarse , so that the dissolution rate of the strengthening phase is slower, so the holding time is correspondingly longer; the holding time of aluminum profiles heated in hot air and heated in a salt bath is quite different; the heating time in a salt bath is much shorter; Most industrial aluminum profiles or bars use vertical air hardening furnaces, and the holding time is calculated when the metal surface temperature or furnace temperature reaches the lower limit of the hardening temperature. The vacuum hardening heating and holding time must ensure that the strengthening phase is fully dissolved in order to obtain the maximum strengthening effect; but the heating time should not be too long, in some cases, it will reduce the performance of the profile.

Many industrial vacuum heat treatment strengthened aluminum profiles such as 2A12, 7A04 and other high-strength profiles, unlike architectural aluminum profiles such as 6063 alloys, can be quenched in air, that is, a small cooling rate can prevent the precipitation of strengthening phases; they are heated from hardening Take it out of the furnace, transfer it to the hardening water tank, and cool it in the air for just a few seconds or even a few seconds, there will be precipitation of the strengthening phase, which will affect the strengthening effect.

Therefore, the hardening transfer time is one of the process parameters that must be specified in the vacuum hardening process of aluminum profiles; that is, the transfer of aluminum profiles from the vacuum hardening furnace to the hardening medium must be completed within the specified maximum transfer time; this time is called the maximum allowable transfer Time or hardening delay time; this time is related to the composition of the alloy, the shape of the profile, and the degree of automation of equipment operation; if conditions permit, the shorter the hardening transfer time, the better; general process regulations: the transfer time of small profiles should not exceed 20s , Large or batch-quenched aluminum profiles should not exceed 40s; for superhard profiles such as 7A04, the transfer time should not exceed 15s.