| The heat treatment of LD11 alouminum alloy was researched in this paper. The mechanical properties of the alloy after different heat-treatments. The fractograph and microstructure of the alloy after heat treatments were observed by SEM and optical microscope. The strengthening mechanism of the alloy was analyzed and the parameters of the heat-treatments were modified.The results show that during solution treatment, the solubility of strengthen phase is proportional to solution temperature. and silicon phase particles coarsen slowly at high solution temperature, which decreases the strengthening effect. There is a small number of precipitates in the alloy solution for short time. while silicon phase will grow when the alloy soluted for a long time. Both of these will decrease the properties of the alloy. for one-step aging treatment, short treatment time will result in incomplete precipitation, which decreases the strength of the alloy. over aging will carry out when aging for a long time. The strengthening particles precipitate completely when aging at lower temperatures. The strengthening particles will re-solute into matrix and forming non-precipitates zone, which decreases the elongation of the alloy. The optimized one-step aging treatment is: solution at 520 for 3.5h, and one-step aging at 165 for 8h.The two-step aging treatment is analyzed by using orthogonal examination. The optimum heat treatment process is: solution at 520 for 3.5h, first aging at 140 for 3h, and then aging at 165 for 3.5h. During the first aging process, strengthening particles grow slowly and do not solute.Some meta-stable phases precipitate from supersaturated aluminum solution. precipitates coarsening speed is low during the second aging process. As a result, the alloy has good extensibility. |
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