Overaged Samples and Growth of Eutectics Mg-6Gd-3.7Nd Based Alloys

摘要

The eutectic structure in Mg-6Gd-3.7Nd based alloy was characterized to be result of a 'quasibinary eutectic reaction' L→α-Mg + β-Mg_5RE. The ST temperature applied was apparently sufficient to melt the GB regions of the as-cast Mg-Gd-Nd based alloy, and transform the eutectic structures to a globular liquid phase enriched with RE elements. High supersaturation of Mg matrix by rare earth (RE) elements after quenching of solution treated Mg-Gd-Nd alloy provides sequential precipitation of different metastable phases: α-Mg (S.S.S.S.) → β'' (Mg_3RE, DO_(19))→ β' (Mg_7RE, BCO) → β_1 (Mg_3RE, FCC) → β (Mg_5RE, FCC). The stable β precipitates grew from the eutectic structure in the form of needle-like precipitates. These needles seem to be a continuation of the βphase presented in the eutectic structure. These β precipitates grow at the expense of smaller β_1 and β precipitates presented in the α-Mg matrix. The combination of HRTEM, TEM with SAED and JEMS simulation was carried out to characterize the nanometer-scale precipitates. Microhardness measurements were performed to reveal the effect of precipitation on the mechanical properties of the alloys.