In order to obtain a good aging effect, under the condition of no overheating, overburning and grain growth, the quenching temperature is higher and the heat preservation time is longer, which is conducive to obtaining a uniform solid solution with supersaturation. In addition, no precipitation will occur during quenching and cooling, otherwise, the precipitated phase will play the role of crystal nucleus in the subsequent aging heat treatment, resulting in partial non-uniform precipitation and reducing the aging strengthening effect. Aging temperature at different aging temperature, the influence of precipitated phase of critical nucleus size, number, composition, grew up and gathered speed is different, if the temperature is too low, due to the diffusion is difficult, g. P area is not easy to form, strength, hardness, low after aging, when the aging temperature is too high, spread easily, supersaturated solid solution precipitation phase in the critical nucleus size is big, aging after strength and hardness is low, which has exerted a limitation. Therefore, all kinds of alloys have suitable aging temperature.
The regression phenomenon of aluminum alloy
The aluminum alloy (such as aluminum-copper) after quenching heat treatment and natural aging is reheated to 200 ~ 250℃ and then quickly cooled to room temperature, the strength of the alloy will decrease, and the properties will be restored to the just-quenched state. If placed at room temperature, normal natural aging can still be performed, just like the newly quenched alloy. This phenomenon is called regression phenomenon. The explanation of the regression phenomenon is that when the alloy is naturally aged at room temperature, the size of the g-p zone is small. When the alloy is heated to a higher temperature, these small g-p zones are no longer stable and re-dissolve into the solid solution. At this time, if the alloy is quickly cooled to room temperature, the alloy will return to the newly quenched state and can still be naturally aged again. In theory, the regression treatment is not limited by the number of times of treatment, but in practice, it is difficult to make the precipitation phase re-dissolve in the regression treatment, resulting in local precipitation in the aging process later, which weakens the aging strengthening effect one by one. At the same time, in the process of repeated heating, the solid solution grain tends to be larger and larger, which is bad for the performance. Therefore, the regression heat treatment is only used to repair the rivet alloy used in aircraft, which can be used to rivet at any time, and no use value for other aluminum alloys.
On 2018-08-08 11:45:46
