doi:

DOI: 10.3724/SP.J.1037.2013.00330

Acta Metallurgica Sinica (金属学报) 2013/49:12 PP.1604-1610

STUDY ON KINETICS OF PRECIPITATION IN A1-0.6Mg-0.9Si-0.2Cu ALLOY FOR AUTOMOTIVE APPLICATION


Abstract:
The kinetics of precipitation in A1-0.6Mg-0.9Si-0.2Cu (mass fraction,%)alloy under different conditions was investigated饰differential scanning calorimetric analyses (DSC) and micro- hardness 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 for β"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:YGP=1-exp [-1.3 x 107texp(-7977/T)], Yβ"=1-exp [-4.7 x l022t2exp(-27484/T)]; for T4P alloy:YAP=1-exp(-2.4 x1013texp(-14345/T)],Yp-1-exp[-2.9 x1011lt2exp(一14392/T)]. In addition, with the increasing of aging time, the whole trend 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.

Key words:AI-Mg-Si-Cu alloy,automotive sheet,nature aging,pre-aging,kinetics

ReleaseDate:2015-03-06 17:47:01



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