The constituent of precipitations phases of aged melt-spun AlMgCu ribbons was characterized by high-resolution transmission electron microscopy and microhardness test. The cooling rate of as melt-spun ribbon was estimated to be 1.60×105 K/s from the empirical relation. The samples were aged at 200 ＆#176;C for 16 h after solution treatment. Two precipitation phases, i.e. Al2CuMg and abnormal amorphous SiO2 were identified in the T6 melt-spun AlMgCu ribbon. The crystal structure and stoichiometric composition of Al2CuMg phase are in good agreement with the reference results [WANG et al （2007; 2005）]. The combined experiments show that the formation of abnormal amorphous SiO2 appears to be associated with the higher cooling rate in melt-spinning process and has no significant effect on the peak hardness.
Microstructure and hardness of twin-roll casting （TRC） process and direct-chill casting （DC） for A8006 alloy with and without homogenization were investigated by means of scanning electron microscopy （SEM）, X-ray diffraction analysis and Vickers hardness measurement. The results show that the eutectic phase of the homogenized TRC alloy becomes fine as the microstructure of the as-cast TRC alloy is refined. The short rodlike eutectic phase of the as-cast TRC alloy is dispersed homogeneously, which is similar to the morphology of eutectic phase of the homogenized DC alloy. After homogenization, elements Fe and Mn in DC and TRC alloys are diffused from eutectic phase to A1 matrix, resulting in the decrease of microhardness. The formability of the as-cast TRC alloy is superior to that of the homogenized DC alloy. For TRC A8006 alloy, the homogenizing cycle can be removed from the subsequent processing.
