1、 Causes of coarse grain products
Under certain conditions, large recrystallized grains will be formed in the structure of aluminum and its alloy plates, bars and forgings during the subsequent heat treatment. The existence of such coarse particles will reduce the mechanical properties of the material and make the surface of the deep drawing parts rough or produce impact cracks. Therefore, to obtain uniform fine grain structure is to produce coarse grain, alloy with chemical composition, uniform annealing system, deformation temperature. The factors such as deformation degree, solution heat treatment temperature, heating speed, annealing temperature and holding time are analyzed.
2、 How to reduce the coarse grain produced in the heat treatment of aluminum plate
Aluminum alloy plate is not easy to deform and produce coarse grains. The general principle of reducing or eliminating coarse grains in production is to consider the above factors and take appropriate control or elimination measures according to the specific situation.
Third, take 3A21 aluminum plate as an example to see the elimination of coarse particles
The following measures can be taken to prevent or eliminate the 3A21 alloy annealing plate which is easy to produce coarse grains:
(1) When 3A21 alloy semi continuous ingot is annealed or hot rolled at high temperature, the temperature must be controlled in the range of 500 ~ 520 ℃.
(2)当Mn和Fe的总质量分数小于1.8%时，w(Mn)=?在1.5%-1.4%时，w(Fe)>应控制0.4%，或w(Ti)=?0.1% ~ 0.2%的钛。
(2) When the total mass fraction of Mn and Fe is less than 1.8%, when w (MN) =? Is 1.5% - 1.4%, w (FE) > should control 0.4%, or w (TI) =? 0.1% - 0.2% titanium.
Annealing in a salt bath is recommended. If air furnace is adopted, high temperature and rapid annealing shall be adopted as far as possible.
(4) Before annealing, the processing rate of the finished product must avoid the critical deformation. Generally speaking, the degree of cold deformation of the finished product should be controlled above 75% before annealing.
For industrial pure aluminum annealed sheet, the following measures can be taken to prevent the generation of coarse particles:
(1) The proper rolling temperature for semi continuous casting of pure aluminum ingot is 350 ~ 500 ℃, the rolling temperature is controlled at the upper limit, and the final rolling temperature is not less than 300 ℃
(2) The cold deformation degree before annealing shall not be less than 50%.
(3) It is better to anneal in salt bath, while in air furnace, the heating speed should be increased as much as possible.
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