Influence of a microalloying addition of Ag on the precipitation kinetics of an Al-Cu-Mg alloy with high Mg:Cu ratio
Influence of a microalloying addition of Ag on the precipitation kinetics of an Al-Cu-Mg alloy with high Mg:Cu ratio
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DOI：
10.1016/j.actamat.2015.07.032
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发表时间：
2015-10
期刊：
影响因子：
9.4
通讯作者：
C. Macchi;A. Tolley;R. Giovachini;I. Polmear;A. Somoza
中科院分区：
文献类型：
--
作者：
C. Macchi;A. Tolley;R. Giovachini;I. Polmear;A. Somoza
研究了Ag微合金化对高Mg：Cu比Al-Cu-Mg合金人工时效过程中Al-1.5wt. %和Al-1.5wt.%的三元和四元合金析出过程的影响Cu-4重量% Mg（~ 0.5重量%）Ag）在175 °C下，结合透射电子显微镜和正电子寿命谱。此外，符合多普勒展宽的正电子-电子湮没辐射被用来提供有关的化学环境周围的空位状缺陷的信息。无银合金的结果表明，从固溶处理温度淬火后立即在过饱和固溶体中形成空位v-Cu-Mg团簇。在早期阶段的老化，这些集群变得更丰富的Cu和Mg和板条的S相（Al 2CuMg）优先形核的位错线。持续的时效导致基体中S相板条之间的等轴相逐渐析出，这被认为是以前认为只有当存在银时才形成的Z相。对于含银的Al-Cu-Mg合金，在淬火后即刻也形成v-Cu-Mg-Ag聚集体，其溶质迁移机制相同。然而，沉淀的S相被抑制在老化和银除了促进加速形成一个更好的分散较小的等轴Z相沉淀。对于这两种合金，没有证据表明Z相之前是任何预沉淀或GP区。结合符合多普勒展宽和显微分析结果表明，Z相具有2的Mg：Cu比，这表明它不同于众所周知的T相（Al 6CuMg 4），该平衡相图表明，应该在具有高Mg：Cu比的Al-Cu-Mg合金中形成。240 °C时效实验表明，三元合金中没有Z相和T相形成，只有S相析出，而四元合金中S相被强烈抑制，主要形成Z相析出。
Effects of microalloying with Ag on the precipitation process in an Al–Cu–Mg alloy with high Mg:Cu ratio have been investigated during artificial ageing of the ternary and quaternary compositions Al–1.5 wt.%Cu–4 wt.%Mg(–0.5 wt.%Ag) at 175 °C, combining transmission electron microscopy and positron lifetime spectroscopy. In addition, coincidence Doppler broadening of the positron–electron annihilation radiation was used to provide information about the chemical environment surrounding vacancy-like defects. The results obtained for the silver-free alloy indicate that, immediately after quenching from the solution treatment temperature, vacancy v-Cu–Mg clusters are formed in the supersaturated solid solution. During the early stages of ageing these clusters become richer in Cu and Mg and laths of theSphase (Al2CuMg) nucleate preferentially on dislocation lines. Continued ageing led to gradual precipitation of an equi-axed phase in the matrix between theSphase laths which is believed to be the cubicZphase thought previously to form only if silver is present. For the silver-containing Al–Cu–Mg alloy, v-Cu–Mg–Ag aggregates also form immediately after quenching and the solute transport mechanisms are the same. However, precipitation of theSphase is suppressed during ageing and the silver addition promotes accelerated formation of a finer dispersion of smaller equi-axedZphase precipitates. For both alloys, no evidence was found that theZphase is preceded by any pre-precipitate or GP zones. Combination of coincidence Doppler broadening and microanalysis results revealed theZphase to have a Mg:Cu ratio of 2 which indicates that it differs from the well knownTphase (Al6CuMg4) which the equilibrium phase diagram indicates should form in Al–Cu–Mg alloys with high Mg:Cu ratios. Additional ageing experiments at 240 °C showed that neither theZphase orTphase are formed in the ternary alloy, but only precipitates of theSphase, while in the quaternary alloy theSphase is strongly suppressed and mainlyZphase precipitates are formed.