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摘要
7055 aluminum alloy is a typical age-hardening alloy whose properties change with microstructural evolution as a result of heat treatment. In this paper, the microstructural evolution of the alloy after solid solution treatment and manual aging is examined using SEM, TEM and HADDF. The precipitation, nucleation and growth mechanisms of theta' and theta'' phases are also analyzed. Results show that, as aging proceeds, the Al-Cu phase gradually enlarges and thickens the following precipitation sequence of supersaturated solid solution (SSSS) -> GPI zone -> GPII zone -> theta'' phase -> theta' phase; some S phases formed during aging, which have two different nucleation mechanisms: homogeneous nucleation and heterogeneous nucleation, the S phases of the latter being marginally larger in size than those of the former. There is a transition in the transformation of (Al3Cu) in GPII zone into theta'-phase (Al2Cu). The orientation relation between theta' phase and Al matrix is (100)(Al)//(100)(theta'), (010)(Al)//(010)(theta'), (001)(Al)//(001)(theta'). According to this relationship, theta' phase has three variants in the matrix: Variants 1, 2, and 3, which represent the theta' phase along {100}(Al), {010}(Al) and {001}(Al). As theta' phase has a special orientation relation with Al matrix (100)(Al)//(100)(theta'), (010)(Al)//(010)(theta'), (001)(Al)//(001)(theta'), theta' phase is distributed in disc form on {001}(Al). Significantly larger S phase can be observed. The orientation relation between S phase and Al matrix is [100](Al)//[100](S), [021](Al)//[010](S), [012](Al)//[001](S). theta' phase grows in step form for a period equaling to 1.75-fold unit cell of theta'. As theta' phase grows, the Cu atoms segregated on the edge of theta' phase are gradually consumed.
- 出版日期2017-12
- 单位青岛理工大学
