6056 aluminum alloy is an Al-Mg-Si-Cu alloy widely used in the automotive and aviation fields. Its strength is 15% higher than that of 6061 aluminum alloy. Its weldability, corrosion resistance and cutting performance are better than 7075 and 2024.
The composition of 6056 aluminum alloy is complex. During the semi-continuous casting process, the ingot structure will deviate from the equilibrium state, resulting in severe dendrite segregation and a large amount of non-equilibrium solidification eutectic structure.
Therefore, 6056 aluminum alloy ingot must be homogenized annealed to eliminate dendrite segregation, minimizing the residual crystalline phase in the matrix, and improving the plasticity of the alloy.
Homogenization annealing treatment is one of the key links to obtain ideal process and mechanical properties of 6056 aluminum alloy. The increase in temperature is conducive to accelerating the diffusion process, that is, accelerating the homogenization process.
The homogenization annealing temperature should be increased as much as possible, but considering the accuracy of the homogenization annealing equipment and the actual production, the homogenization temperature is selected at 540 ℃.
Through the observation of DSC curve of 6056 aluminum cast rod after homogenization treatment at 540 ℃×12 h, the endothermic peak at 554 ℃ has disappeared, that is to say, after the homogenization annealing treatment, the non-equilibrium freezing point eutectic structure mostly disappears.
With the progress of homogenization annealing treatment, the strength of 6056 aluminum alloy begins to gradually decrease, and the plasticity increases. The strength of 6056 aluminum alloy treated by homogenization annealing treatment at 540 ℃×6 h decreases to 214 MPa, and the ductility increases to 6.0%.
The strength of 6056 aluminum treated by homogenization annealing at 540 ℃×12 h decreases to 205 MPa, and the ductility increases to 16.5%. This is due to the dissolution of the second phase that hinders the movement of dislocations and pinned grain boundaries during the homogenization process, which reduces the strength of 6056 aluminum alloy.
The casting stress is gradually eliminated, the alloy dendritic segregation and non-equilibrium eutectic structure are eliminated, the structure becomes uniform, and the alloy plasticity is enhanced, so the elongation rate is increased.
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