采用差示扫描量热法(DSC)和硬度测量方法对汽车用Al—0.6Mg—0.9Si—0.2Cu(质量分数, %)合金不同状态析出动力学进行了研究. 结果表明,T4态合金升温到100—-150℃时, DSC曲线出现低温析出峰,而T4P态合金无此低温析出峰; 经过T4P处理的合金其β″相析出峰位向低温移动.利用A—J—M方法计算合金不同相析出动力学参数,结果表明, T4和T4P态合金GP区溶解激活能分别为66和119 kJ/mol, β″相析出激活能分别为114和60 kJ/mol;T4态合金的溶解和析出动力学方程分别为:Y_GP=1-exp[-1.3×10⁷t exp(-7977/T)],Y_β″=1-exp[-4.7×10²²t²exp(-27484/T)];T4P态合金的溶解和析出动力学方程分别为:Y_GP=1-exp[-2.4×10¹³ t exp(-14345/T)],Y_β″=1-exp[-2.9×10¹¹t² exp(-14392/T)].此外, 在185℃时效过程中, 随着时效时间的延长, T4和T4P态合金的硬度均先不断增加达到峰值后趋于平缓,但是T4态合金经20 min时效处理后出现硬度下降, 而T4P态合金无此现象,利用GP区回溶和β″相析出动力学对此变化规律进行了很好的解释.

The kinetics of precipitation in Al—0.6Mg—0.9Si—0.2Cu (mass fraction, %) alloy under different conditions was investigated by differential scanning calorimetric analyses (DSC) and microhardness measurements. The results show that, an exothermic peak at about 100—-150℃ can be observed in the DSC curve for the nature aged (T4) alloy, but no peak for the pre—aged (T4P) alloy, and the peak corresponding with β″ phase moves toward the low temperature zone for T4P alloy. The fraction of transformation Y, the rate of transformation dY/dT, and the kinetic parameters such as activation energy Q and frequency factor k₀ for GP zones dissolution and β″phase transformation were calculated by Avrami—Johnson—Mehl equation. The values of activation energy for GP zones dissolution after natural aging and pre—aging were 66 and 119 kJ/mol, respectively, and the values forβ″phase formation after natural aging and pre—aging were 114 and 60 kJ/mol, respectively. The kinetics expressions were obtained as follows, for T4 alloy:Y_GP=1-exp[-1.3×10⁷t exp(-7977/T)],Y_β″=1-exp[-4.7×10²²t² exp(-27484/T)];for T4P alloy: Y_GP=1-exp[-2.4×10¹³ t exp(-14345/T)],Y_β″=1-exp[-2.9×10¹¹t² exp(-14392/T)].In addition, with the increasing of aging time, the wholetrend of hardness changing for pre—aged alloy is increasing at first, and then keeps constant basically,but for the nature aged alloy, the hardness decreases after aging at 185℃ for 20 min, which was explained by the kinetics obtained above.