中文摘要：

制备具有不同原位Al2O3颗粒含量的近液相线铸造Al-6.8Cu合金,在580℃、590℃、600℃和610℃进行二次加热并保温10 min、20 min、40 min和60 min,淬火固定半固态组织。采用光镜观察其组织,利用平均截线法统计其晶粒尺寸,分析不同颗粒含量对近液相线铸造Al-6.8Cu合金半固态组织的影响规律。结果表明,原位Al2O3颗粒对Al-6.8Cu合金的铸态组织没有明显的球化和细化作用,但是在合金的二次加热过程中对合金的晶粒长大行为具有抑制作用,当原位Al2O3颗粒含量达到3.6 wt%时,对晶界已经产生良好的钉扎效果,使合金保持细小均匀的等轴晶组织特征,能够满足后续的半固态成形工艺要求。

英文摘要：

The microstructure of in-situ reactive near-liquidus cast X wt.% Al2O3 /Al-6.8Cu（X=0;3.6;4.3;5.3） after 10 min、20 min、40 min and 60 min at 580 ℃、590 ℃、600 ℃and 610 ℃were observed using OM.And the grain sizes were measured using a mean linear intercept method to analyze the effects of different weight fraction of in-situ Al2O3 particles on the semi-solid microstructure of near-liquidus cast Al-6.8Cu alloy.It was shown that the in-situ Al2O3 particles can not make near-liquidus cast Al-6.8Cu alloy with fine and globular microstructure but control evidently grains growth by pinning effect during reheating.the pinning effect of in-situ Al2O3 particles on grain growth in the two-phase（liquid ＋ solid） region of near-liquidus cast Al-6.8Cu alloy was significant when weight fraction of in-situ Al2O3 particles was up to 3.6 wt.%,which made microstructures of the alloy keep as-fine and equiaxed grains characteristics and could meet the requirement of subsequent semi-solid processing.