[China Aluminum Industry Network] How the age hardening of aluminum rods and (aluminum alloys) without homogenization is performed and completed.
The phenomenon that the strength and hardness of the quenched aluminum alloy significantly increases with the passage of time is called aging, and the age hardening of the aluminum alloy is also called. This is one of the important methods for strengthening aluminum alloys.
According to the definition, the premise of the aging strengthening of aluminum alloys is to first perform quenching to obtain a saturated single-phase structure. In a solid solution obtained by quench hardening, not only is the solute atom supersaturated, but also the vacancy (crystal point defect) is supersaturated, ie, in a double supersaturated state. The study shows that the higher the temperature of aluminum alloy solution treatment, the greater the degree of supersaturation after treatment, and the greater the effect of aging hardening after aging. Therefore, the principle of solution temperature selection is: In the premise of ensuring that the alloy does not burn, the solution temperature is increased as much as possible.
Solution-treated aluminum alloys undergo an aging process when they are left at room temperature or at a certain temperature. This process is essentially the process of precipitation of the second phase from the supersaturated solid solution. This process is carried out by shaping and growth and is a diffusion-type solid phase transition. It proceeds in the following order: What are the factors affecting the age-strengthening effect in a → GP → θ'' phase → θ' → θ phase?
Aging is carried out in a certain order, and the enhancement effect is affected by the following factors.
(1) aging temperature. Fixed aging time, the relationship between aging temperature and aging strengthening effect (hardness) for the same composition of the alloy. At a certain aging temperature, a large hardening effect can be obtained. This temperature is called the preferred aging temperature. The ageing temperature of the different compositional alloys for obtaining a greater aging strengthening effect is different. Statistics show that the following relationship exists between the preferred aging temperature and the alloy melting point: T0 = (0.5–0.6)T
(2) The aging time. The peaks of hardness and strength appear at the end of the phase θ′′ and the initial phase of the θ′ transition phase. After the phase θ′ has elapsed, the softening begins. When a large number of θ phases occur, softening is already severe. Therefore, within a certain aging temperature, in order to obtain a larger aging strengthening effect, there should be a better aging time, that is, the time required for the transition from θ′′ to θ′.
(3) Quenching temperature, quenching and cooling speed and quenching transfer time. Practice has proved that the higher the quenching temperature, the faster the quenching cooling rate, the shorter the intermediate time of quenching, the greater the degree of supersaturation of the obtained solid solution, and the greater the strengthening effect after aging.
(4) aging process. Aging can choose single-stage or graded aging. Single-stage aging refers to an aging process conducted at or below 100°C. The process is simple, but the uniformity of the structure is poor, and the tensile strength, yield strength, conditional yield strength, fracture resistance, and stress corrosion resistance performance are difficult to get a good match. Fractionation aging is performed twice at different temperatures or multiple aging.
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