Early decomposition of supersaturated solid solutions of Al–Zn–Mg casting alloys

Characterization of phase development in commercial Al-Zn-Mg(-Mn,Fe) alloy with and without Sc,Zr-addition

“…Owing to the strengthening effect of the GP zones and/or clusters, the microhardness values of the alloys increase continuously during ageing at RT after quenching due to the solute clusters growing and GP zones formation in agreement with the others for the Al--Zn-Mg-based alloys (e.g. [19,20]).…”

“…Typically, the formation of coherent Guinier-Preston (GP) zones and/or Zn,Mg-rich clusters precedes the formation of the semicoherent intermediate precipitates and incoherent equilibrium precipitates [2][3][4][5][6][7][8]16]. In general, the early precipitation stages can be universally abundant in Al-based alloys and are known to affect the resistivity and (micro)hardness [19][20][21]. Many authors have attempted to explain changes of electrical resistivity and microhardness at the beginning of the precipitation kinetics in the Al-based alloys due to the formation of the GP zones and/or clusters [8,[19][20][21].…”

“…In general, the early precipitation stages can be universally abundant in Al-based alloys and are known to affect the resistivity and (micro)hardness [19][20][21]. Many authors have attempted to explain changes of electrical resistivity and microhardness at the beginning of the precipitation kinetics in the Al-based alloys due to the formation of the GP zones and/or clusters [8,[19][20][21]. Preliminary positron annihilation spectroscopy (PAS) measurements in the AlZnMg alloy show that the positrons annihilate at traps associated with GP zones and/or small clusters and are characterized by a positron lifetime of 0.213 ns.…”

“…The effect of Sc in the Al-Zn-Mg system was studied by several authors with controversial results concerning the question of whether the addition of Sc accelerates or retards the decomposition of the supersaturated solid solution of the Al-Zn-Mg system. The mentioned controversy in the literature may originate from observations in different stages of the ageing process (there was a different content of Zn and Mg or Cu-addition in some materials [19,20]). On the other hand, GP zone formation occurs at RT which is only possible if diffusion is assisted with a substantial amount of non-equilibrium quenched-in vacancies [28].…”

Effects of germanium on quench sensitivity in Al–Zn–Mg–Zr alloy

“…Only those bound to cluster-forming atoms and free vacancies were favorable for promoting the formation of coarse η phase. Many studies have also shown that the vacancies strongly interacted with solute by forming vacancies-solute complexes [25,26,28]. If solute was a cluster-forming constituent, for instance in Al-Zn-Mg alloy the cluster-forming constituents were Zn and Mg atoms, the solute migration rate would be accelerated by continual interchange of the vacancies between cluster constituents and the neighboring solute atoms [23].…”