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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Al_(11)La_3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Al_(11)La_3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 morphology, size and hardness of AZ91 alloy with different La content were investigated by TEM, OM, SEM and Vickers hardness measurements. The effects of discontinuous β phase and Al 11 La 3 phase on the hardness of the alloy and its mechanism, and calculate the diffusion coefficient of Al atoms in the aging process.The results show that the AZ91 alloy with different La content at 170 ℃, the La content of 0.16% 24 h reaches the maximum hardness of 138 HV. Prolonging the aging time and changing the content of La, the discontinuous desolvation can be transformed into the continuous stripping phase of lamella, the diffusion coefficient of Al atoms can be reduced, and the number of discontinuous β phase can be affected , Size and distribution of grain boundary, although the morphology of Al_ (11) La_3 phase at the grain boundary is not affected by the heat treatment process, but it restricts the growth of β-phase.It can be seen that the control of La content and aging time can improve the discontinuity (sheet) β phase size and quantity, effectively improve the toughness of the alloy.