时效工艺对Al-Li-Cu-Mg合金组织及力学性能的影响

Effects of aging treatment on microstructure and properties of Al-Li-Cu-Mg alloy

通过金相显微镜、透射电镜微和室温拉伸等手段,研究了热处理制度对新型Al-Li-Cu-Mg合金微观组织演变和力学性能的影响。结果表明,该合金主要存在四种第二相:立方AlCu2Mn相、棒状AlxCuxMnx、球状δ'相和片层T1相。前两相为高温结晶相,对合金沉淀强化贡献较少,后两相分别为自然时效和人工时效主要强化相。随着时效温度的升高和时间的延长,合金中G.P.区、球状δ'相等溶解,针状T1相析出,并在温度达到160℃时T1相析出速度明显高于δ'相的溶解,并与δ'相形成对合金的复合强化;180℃后在晶界处发生回复和再结晶。合金的强度随微观组织的变化显著,在90～150℃时,随着时效温度升高和时间延长,合金的硬度和强度先降低后提高;高于160℃时,合金强度和硬度随时效进行迅速增高,20 h即达到时效峰值;高于180℃后,时效达到峰值后随时间延长因发生再结晶而使合金强度和硬度降低。初步判定合金时效强化理想工艺应为(160～170)℃×20 h。

The effects of aging treatment on microstructure and mechanical properties of new A1-Li-Cu-Mg alloy were studied by optical microscopy, transmission electron microscopy and tensile tests. Four typical second phases such as cubic-typed A1Cu2Mn, rod-like AlxCuxMnx, spherical δ＇ and lamellar T1 were investigated. The former two phases are the high temperature crystal phases which make little contribution to the precipitation strengthening, while the last two phases are the main strengthening phases corresponding to the natural and artificial aged processing. With the increase of the aging temperature and the time, the G.P. zones and spherical δ＇ are dissolved, in contrast, lamellar T1 is precipitated and the forming rate exceeds the dissolved δ＇ phase and in company with δ＇ which significantly improve the strength. When the aging temperature reaches 180 ℃, recovery and recrystallization occurs in the grain boundary. The hardness and strength change significantly with the changes of the mierostructure. They first decrease and then increase with the increase of the aging time and temperature at 90-150 ℃. When the temperature is over 160 ℃ the hardness and strength of the alloy increases fast and reached aging peak within 20 h. Once the temperature is over 180 ℃, the hardness and strength are decreases with time increasing after the peak aging due to the reerystallization. It can be initial confirmed that the optimum aging treatment is 160-170 ℃ for 20 h.