半固态铸造高Cu含量Al-Cu合金的组织及形成机制

Microstructure and Formation Mechanism of Semi-solid Casting Al-Cu Alloy Containing High Cu

通过对较高Cu含量的铝合金微观组织的观察,研究了半固态铸造的Al-10Cu、Al-20Cu和Al-40Cu合金中初生α-Al枝晶、共晶晶粒和初生θ相的形貌、尺寸的变化规律以及形成机制。结果表明,半固态铸造Al-10Cu、Al-20Cu合金的初生α-Al呈近等轴的球状或蔷薇球状,其大小为50～80μm;半固态铸造的过共晶Al-40Cu合金中初生CuAl2的形貌由较粗较长的条状转变为粒状或长径比较小的短棒状或近等轴的颗粒状,其平均尺寸小于80μm,基本消除了粗长的初生CuAl2,改善了晶粒形貌;与普通铸造相比,半固态铸造3种Al-Cu合金的组织得到显著的改善,完全能够达到工程应用的要求。经强烈搅拌制备的半固态Al-Cu合金中的α-Al晶粒的生长可以看作内生生长,这是高Cu含量的铝合金能形成近等轴的球状、蔷薇球状、较小的短棒状、近等轴的颗粒状组织的原因。

Morphology of primary α-Al dendrite and eutectoids as well as primary θ phase and size variation,and formation mechanism of semi-solid casting Al-Cu alloy containing 10% Cu,20% Cu and 40% Cu were investigated by SEM (scanning electron microscope),OM (optical microscope). The results reveal that primary α-Al phase with size of 50~80 μm exhibits near-equiaxed globular structure or rosette in semi-solid Al-10Cu and Al-20Cu alloy,while primary CuAl2 phase in semi-solid Al-40Cu alloy is fully converted from coarse long ribbon into particle or short rod with small length-diameter ratio or near-equiaxed particle with the average size lower than 80 μm,greatly improving the grain morphology. Compared with that by conventional casting,the microstructure of semi-solid casting Al-Cu alloy is significantly improved,fully meeting the demands of engineering application. Primary α-Al phase exhibits in-situ growth in semi-solid Al-Cu alloy in the condition of intensely stirring,which is responsible for the formation of near-equiaxed globular structure or rosette structure or small short rod and near-equaixed particle.