Effects of Si additions on the precipitation hardening response in Al-Cu-Mg(-Ag) alloys

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The effects of Si additions on the precipitation hardening response of Al-4Cu-0.3Mg(-0.4Ag) (wt%) alloys have been examined systematically using transmission electron microscopy. The addition of Si to the Al-4Cu-0.3Mg alloy produces an increase of up to 30 VHN in the maximum hardness obtainable during ageing at 200°C and, for Si contents in the range 0.3-0.7 wt%, the maximum hardness exceeds that achievable in the Al-4Cu-0.3Mg-0.4Ag alloy (∼140 VHN) under similar ageing conditions. Maximum hardness of the Al-Cu-Mg-Si alloys is associated with coexistence of uniform, fine-scale distributions of {100}α plates of θ' and <100>α laths of Q phase (Al4Cu2Mg8Si7). The addition of ≥ 0.2 wt% Si to the Al-4Cu-0.3Mg-0.4Ag alloy results in complete suppression of the Ω phase that dominates the microstructure of the quaternary alloy. However, the hardness of the Si-modified alloys may still be enhanced with appropriate Si additions, even in the absence of the Ω phase.

Original languageEnglish
Pages (from-to)1251-1256
Number of pages6
JournalMaterials Science Forum
Issue numberPART 2
Publication statusPublished - 1 Dec 1996


  • Al-Cu-Mg(-Ag) alloys
  • High strength Al alloys
  • Precipitation hardening
  • Si additions

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