通过透射电子显微技术(TEM)研究了Mg-6 wt％Zn-1 wt％Mn (ZM61)合金在单级和双级时效过程中过渡相β1'和β2'的演变规律以及β1'杆状相在α-Mn颗粒上异质形核的原因.ZM61合金在不同温度的硬化曲线(130、160、180、200、230℃)均表明:与单级时效相比,双级时效的硬化效果更好同时硬化速率更快.由于β1'杆状相的表面能和形核能垒均小于β2'盘状相,因此,峰时效之前主要发生β1'杆状相的快速形核和伸长;β1'杆状相体积分数的增加在带来硬度增加的同时也提升了体系的应变能,β2'盘状相取代β1'杆状相可以释放这一累积的应变能,因而过时效阶段主要发生β2'盘状相对β1'杆状相的逐步取代.ZM61合金在预时效后(90℃/24 h),组织中存在高弥散度的G.P.区(～10 nm),它们可以作为第二级时效过程中β1'杆状相的形核核心,从而大幅提升了杆状相的弥散度.由于β1杆状相在α-Mn颗粒上异质形核可以形成β1'/α-Mn共格界面,取代之前的非共格的α-Mn/α-Mg界面,从而有效降低了体系的界面能,因此时效态组织中普遍存在β1'杆状相在α-Mn颗粒上异质形核的现象.
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