Cu含量对SiC/Al-Mg-Si-Cu复合材料自然时效负面效应的影响

Influence of Cu Content on the Negative Effect of Natural Aging in SiC/Al-Mg-Si-Cu Composites

通过硬度测试、DSC分析及TEM观测研究了Cu含量对17%SiC(体积分数)颗粒增强Al-1.2Mg-0.6Six Cu(x=0、0.2、0.6、1.0、1.2,质量分数,%)复合材料自然时效负面效应的影响规律,并与未增强合金进行了比较。结果表明,与不含Cu的情况相比,添加Cu可以减小复合材料及铝合金在直接人工时效态和先自然时效后人工时效态的硬度差值(ΔH)。其原因在于Cu可以促进人工时效时β"相析出,并形成稳定性良好的L相(一种含Cu纳米相,不易粗化)。然而,Cu会加剧自然时效团簇形成,这些团簇难以在人工时效时转变成析出相,不利于人工时效硬化。因此,Cu对于抑制自然时效的负面效应既存在有利影响,也存在不利影响,表现为ΔH随Cu含量增加产生波动变化。此外,随Cu含量增加,Cu抑制自然时效负面效应的作用在复合材料和合金中表现出不同的规律。与不含Cu的样品相比,复合材料中添加0.2%Cu即可显著降低ΔH,但在铝合金中Cu需增加至0.6%才出现明显效果。这种差异主要源自2方面原因:其一,在铝合金中添加0.2%Cu即会明显促进自然时效团簇的形成;而复合材料中界面及位错湮灭了空位,故0.2%Cu对自然时效团簇析出行为的影响不大;其二,复合材料中添加0.2%Cu便可形成L相,但合金中却不会。

Most Al-Mg-Si-Cu alloys and their composites are affected by natural aging processes.When natural aging precedes artificial aging,it impairs the hardening during artificial aging.This study investigates the influence of Cu content on the negative effects of natural aging in silicon carbide(SiC)(17%volume fraction)reinforced Al-1.2 Mg-0.6 Si-x Cu(x=0,0.2,0.6,1.0,and 1.2,mass fraction,%)composites.The samples were investigated by hardness analysis,DSC,and TEM.For comparison,Al-1.2 Mg-0.6 Si-x Cu alloys were examined by the same methods.The difference in hardness(ΔH)between samples in the direct artificial aging state and those that were naturally aged for 14 d before artificial aging were compared with Cu-containing and Cu-free samples.The values ofΔH were lower in the Cucontaining samples,indicating that Cu mitigated the negative effects of natural aging.However,the values ofΔH fluctuated as the Cu content increased.DSC and TEM results revealed the addition of Cu promoted the precipitation ofβ"phases(the primary strengthening phases in Al-Mg-Si alloys)and the formation of stable L phases during artificial aging.This morphological behavior explained why Cu inhibited the negative effects of natural aging.On the downside,Cu aggravated the formation of clusters during natural aging,which resisted precipitation and negatively affected the hardening during artificial aging.The contrasting beneficial and adverse influence on the effects of natural aging caused the fluctuations inΔH.The mitigating effect of Cu differed between the 17%SiC/Al-1.2 Mg-0.6 Si-x Cu composites and Al-1.2 Mg-0.6 Si-x Cu alloys.A small amount of Cu(0.2%,mass fraction)significantly reduced theΔH of the composite,but the Al alloy with 0.2%Cu failed to elicit this effect.This result can be explained by two observations.First,the DSC results showed that in the Al-1.2 Mg-0.6 Si-0.2 Cu alloys,Cu significantly aggravated the clustering of solute atoms during natural aging,whereas in the 17%SiC/Al-1.2 Mg-0.6 Si-0.2 Cu composites,formation of clusters was low because the vacancies were annihilated by interfaces and dislocations.Second,the TEM results revealed the presence of L phases in the 17%SiC/Al-1.2 Mg-0.6 Si-0.2 Cu composites,which were absent in the Al-1.2 Mg-0.6 Si-0.2 Cu alloys.