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<p>L-phase precursors were discovered in AA6061-T8 aluminium alloy using high-resolution scanning transmission electron microscopy. Precipitates with a lateral size of approximately 2&#xa0;nm form after cold rolling and artificial ageing. These fine L-phase precursors are characterized by Cu-rich column(s) that form single or multiple C sub-units as the structural core. Based on the arrangement of C sub-units, two distinct types of L-phase precursors are observed, each exhibiting different initial structural configurations. Type I precursors initiate from a single C sub-unit, which subsequently develops into an in-plane mirror-symmetric structure in cross section. Growth of Type I precursors proceeds through further addition of Cu atoms that substitute the Si atoms in the precursor’s periphery. Type II precursors are characterized by two Cu columns that form two C sub-units in a rotationally symmetric configuration. The formation of both types of the L-phase precursor begins with Cu substitution for Si within the Guinier–Preston (GP) zones during early stages of precipitation. In a specific 2<i>β</i>″ type GP zone, Cu substitution follows a well-defined pattern. Density functional theory (DFT) calculations indicate that Cu substitution behaviour in 2<i>β</i>″ type GP zones is following the pathway which overcomes the minimum energy barrier, subsequently evolving into an L-phase precursor with a characteristic Cu distribution pattern. These findings establish a direct link between atomic-scale Cu substitution behaviour and the early-stage evolution of Cu-rich precipitates in 6xxx aluminium alloys.</p>

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The Formation of L-Phase Precursor Originated from Cu-Containing Guinier–Preston Zone in Al–Mg–Si–(Cu) Alloys

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月27日

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  • Yi Wang,
  • Jinghui Chen,
  • Jan Halvor Nordlien,
  • Jostein Røyset,
  • Jonas Kristoffer Sunde,
  • Eva Anne Mørtsell,
  • Xiaorong Zhou

摘要

L-phase precursors were discovered in AA6061-T8 aluminium alloy using high-resolution scanning transmission electron microscopy. Precipitates with a lateral size of approximately 2 nm form after cold rolling and artificial ageing. These fine L-phase precursors are characterized by Cu-rich column(s) that form single or multiple C sub-units as the structural core. Based on the arrangement of C sub-units, two distinct types of L-phase precursors are observed, each exhibiting different initial structural configurations. Type I precursors initiate from a single C sub-unit, which subsequently develops into an in-plane mirror-symmetric structure in cross section. Growth of Type I precursors proceeds through further addition of Cu atoms that substitute the Si atoms in the precursor’s periphery. Type II precursors are characterized by two Cu columns that form two C sub-units in a rotationally symmetric configuration. The formation of both types of the L-phase precursor begins with Cu substitution for Si within the Guinier–Preston (GP) zones during early stages of precipitation. In a specific 2β″ type GP zone, Cu substitution follows a well-defined pattern. Density functional theory (DFT) calculations indicate that Cu substitution behaviour in 2β″ type GP zones is following the pathway which overcomes the minimum energy barrier, subsequently evolving into an L-phase precursor with a characteristic Cu distribution pattern. These findings establish a direct link between atomic-scale Cu substitution behaviour and the early-stage evolution of Cu-rich precipitates in 6xxx aluminium alloys.