Title of article :
Secondary precipitation in Al–Zn–Mg–(Ag) alloys Original Research Article
Author/Authors :
C.E Macchi، نويسنده , , A Somoza، نويسنده , , A Dupasquier، نويسنده , , I.J. Polmear، نويسنده ,
Issue Information :
دوهفته نامه با شماره پیاپی سال 2003
Pages :
8
From page :
5151
To page :
5158
Abstract :
Secondary ageing of age-hardenable aluminium alloys occurs at temperatures below the solvus of GP zones after a preliminary ageing at a higher temperature. The phenomenon has technological interest, as it may be included in heat treatments giving a substantial benefit on the mechanical properties. In the present work, positron annihilation lifetime spectroscopy (PALS) is applied in combination with Vickers hardness measurements for an investigation on secondary ageing of Al–4wt.%Zn–3wt.%Mg–xAg, where x=0, 0.1, 0.2, 0.3, 0.5 wt.%. Ageing regimes have been characterised by the substantially different evolutions that are observed. The results shed light on the interplay between the formation of coherent solute aggregates (clusters or GP zones) and the precipitation of semi-coherent or incoherent precipitates, which are in competition to control the hardening effects. PALS data show that secondary ageing in the ternary Al–Zn–Mg alloys produces coherent aggregates even in the presence of a well-developed stage of semi-coherent or incoherent precipitation that is obtained if the alloys are first aged to peak hardness. In the presence of Ag, on the contrary, the effects of coherent aggregation during secondary ageing are observed only if the preliminary ageing is interrupted well before reaching peak hardness.
Keywords :
Positron annihilation spectroscopy , Aluminium alloys , Age hardening , Secondary ageing
Journal title :
ACTA Materialia
Serial Year :
2003
Journal title :
ACTA Materialia
Record number :
1140528
Link To Document :
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