用TEM, OM, SEM和Vickers硬度仪测定、表征了铸态、固溶+时效态下不同La含量 AZ91合金的显微组织和析出相的形态和尺寸以及硬度变化, 研究了不连续β相和Al11La3相的形貌对合金硬度的影响及其机理, 并计算时效过程中 Al原子的扩散系数. 结果表明, 不同La含量AZ91合金在170 ℃时, La含量为0.16%的合金时效24 h达到的硬度最大, 为138 HV; 延长时效时间和改变La含量可使不连续脱溶相转变为板条状连续脱溶相, 降低Al原子的扩散系数, 从而影响不连续β相的数量、大小与分布; 晶界处的Al11La3相的形貌虽不受热处理过程影响, 但却制约β相的长大. 可见控制La含量和时效时间, 可改善不连续(片层)β相的尺寸和数量, 有效地提高合金强韧性能.
The changes of microhardness, microstructures and precipitation phase morphologies of as--cast and aged AZ91 alloys with different La were characterized by TEM, OM, SEM and Vickers. The influences of discontinuous β phase and Al11La3 on AZ91 magnesium alloy were discussed and the diffusion coefficient of Al atom in the aging process was calculated. The results showed that the alloy with 0.16%La aged at 170 ℃ for 24 h has the largest hardness (138 HV). By extending aging time and adding La element, the discontinuous precipitation phases was transformed into continuous lath--sharped phases and the diffusion coefficient of Al atom was decreased, the volume and distribution of β phase were changed. During the process of heat treatment, the topography of Al11La3 in grain boundary was not changed, but the anchoring effect of Al11La3 restricted the growth of β phase. By controlling the content of La and parameters of aging treatment, the volume and size of β phase were changed, in the mean time the strengthening and toughness properties of alloys can been improved effectively.
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