On 2018-08-08 14:48:54
T6 heat treatment and T7 heat treatment of aluminum alloy difference between
Can T6 products also be T7? Is the temperature all the same? What is the meaning of T7 stabilization?
1、 T6 -- solution treatment plus complete artificial aging is applicable to products that are not subject to cold processing after solution heat treatment (straightening and leveling can be carried out, but the mechanical property limit will not be affected).
T7 -- solution treatment plus stabilization treatment is applicable to the products whose strength exceeds the peak point on the aging curve during artificial aging to obtain some important characteristics after solution heat treatment.
2、 Solution treatment: refers to the heat treatment process in which the alloy is heated to a high temperature single-phase area and kept at a constant temperature, so that the surplus phase is fully dissolved in the solid solution and then cooled (cooled) quickly to obtain supersaturated solid solution.
Stabilizing treatment: heat treatment to keep the shape and size change within the specified range under the condition of long-term service
3、 Incomplete artificial aging: adopt relatively low aging temperature or relatively short holding time to obtain excellent comprehensive mechanical properties, that is, obtain relatively high strength, good plasticity and toughness, but the corrosion resistance may be relatively low.
Complete artificial aging: high aging temperature and long holding time are used to obtain the maximum hardness and tensile strength, but the elongation is low.
Strengthening principle of aluminum alloy:
Age hardening of aluminum alloy is a very complex process, which not only depends on the composition and aging process of the alloy, but also depends on the defects caused in the production process, especially the number and distribution of vacancies and dislocations. At present, it is generally believed that age hardening is the result of the formation of hardening zone by solute atom segregation. When the aluminum alloy is quenched and heated, vacancies are formed in the alloy. During quenching, these vacancies are "fixed" in the crystal because of the fast cooling. Most of these vacancies in supersaturated solid solution are combined with solute atoms. Because the supersaturated solid solution is in an unstable state, it must change to the equilibrium state. The existence of vacancy accelerates the diffusion speed of solute atoms, thus accelerating the solute atom segregation.
The size and quantity of hardening zone depend on quenching temperature and cooling rate. The higher the quenching temperature is, the higher the vacancy concentration is, the more the number of hardened areas is, and the smaller the size of hardened areas is. The larger the quenching cooling rate is, the more the fixed space in the solid solution is, which is beneficial to increase the number of hardened areas and reduce the size of hardened areas.
One of the basic characteristics of precipitation hardening alloy system is the change of equilibrium solid solubility with temperature, that is, the increase of solid solubility with temperature. Most of the aluminum alloys that can be heat treated and strengthened meet this condition.