Abstract
The Al-Zn-Mg-Cu alloy containing Zr will precipitate fine and dense Al3Zr particles that coherence with the aluminum base after two-stage homogenization. The dispersed phase can inhibition of recrystallization and grain growth effectively. After the solid solution treatment, the η(MgZn2) phase is not easily to precipitated on the coherence Al3Zr during the quenching process. The solid solution atoms are retained in the aluminum base, so after the aging treatment, the alloy can maintain high mechanical properties and low quenching sensitivity. The deformation can introduce the stored energy into the alloy. The recrystallization ratio will increase with the amount of cold rolling. In addition, the coherence and fine Al3Zr particles alloy will be transformed into incoherence with higher energy after deformation treatment. Although it still can inhibit recrystallization and grain growth effectively, it will increase the chance of precipitation of the η(MgZn2) phase on the Al3Zr particles during the quenching process. It will result in a serious quenching sensitivity. With the increase in deformation amount, the quenching sensitivity will be more obvious.
The one-stage homogenization alloy precipitates coarser and sparser incoherent Al3Zr particles, which leads to its effect of inhibiting recrystallization and grain growth is not as good as the two-stage homogenization. The cold working does not change the incoherence between Al3Zr particles and the interface, so the amount of cold working does not cause a difference in the quenching sensitivity. Although the incoherence Al3Zr particles will increase the chance of precipitation of the η(MgZn2) phase on the dispersed phase during the quenching process. However, its number is less than that of the two-stage homogenized alloy, which means that the η(MgZn2) phase has fewer sites for heterogeneous nucleation. Therefore, the decline of the mechanical properties of the alloy is effectively limited. Its quenching sensitivity is better than that of the processed two-stage homogenized alloy.
According to the research results, the two-stage homogenization can improve the mechanical properties of the alloy, but the quenching sensitivity will be significantly increased with a high amount of deformation. Therefore, the two-stage homogenized alloy is suitable for thin plates, which can easy to quench quickly, while the one-stage homogenization precipitates sparse and incoherent Al3Zr particles. It is easier to precipitate the equilibrium phase during the quenching process, but it can maintain the mechanical properties and quenching sensitivity of the alloy. It is more suitable for the production of thick materials than the two-stage homogenized alloy. In summary, homogenization treatment will change the grain size and improve the mechanical properties. It is still necessary to pay attention to the interfacial relationship between the dispersed phase and the aluminum base to achieve the purpose of reducing the quenching sensitivity.