Role of vacancies on the precipitation processes in Zr modified aluminum based alloys

Mukhopadhyay, A. K.; Shiflet, G. J.; Starke, E.A.

doi:10.1016/0956-716x(90)90261-e

Cited by 31 publications

(15 citation statements)

References 20 publications

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“…The main mechanisms causing the difference in k values are thought to be the increased presence of subgrain boundaries and dislocation in alloys with Al 3 Zr particles [55], which would enhance formation and coarsening of precipitates, and trapping of vacancies by Cr and Zr atoms, which would reduce coarsening rates. Mukhopadhyay et al [56], indicated that the addition of Zr to an Al-Zn-Mg alloy retards GP zone and η′ formation and slows down η precipitation, whilst other research has suggested an enhancement of artificial ageing [55]. It is believed that the slightly lower k value obtained for the Cr containing 7xxx alloys (Table 2) is mainly caused by increased presence of subgrain boundaries and dislocation in alloys with Al 3 Zr particles; whilst also vacancy trapping by Cr might be involved.…”

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confidence: 99%

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Starink

2003

Metall Mater Trans A

113

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A physically-based model for the electrical conductivity of peak aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the η and the S phase solvus (using a regular solution model), taking account of the capillary effect and η coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles and precipitates) and solute depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) along with energy dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr containing alloys and Cr containing alloys under various ageing conditions, achieving an accuracy of about 1% in predicting unseen conductivity data from this set of alloys.

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confidence: 99%

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Starink

2003

Metall Mater Trans A

113

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“…Similarly, from the TEM observations it was evidenced that either Zr or Cr had no noticeable effect on the final precipitates of the alloys [21], although theories indicate that Zr affects precipitation kinetics by retarding GP zones and  formation and slowing down  precipitation [24]. This effect might lead to smaller size of  precipitates in Zr-containing alloys than those in Cr-containing alloys, which was also discerned by Conserva and Fiorini [Ref.…”

Section: Discussionmentioning

confidence: 64%

Identification and analysis of intermetallic phases in overaged Zr-containing and Cr-containing Al–Zn–Mg–Cu alloys

Starink

2011

Journal of Alloys and Compounds

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This paper investigates the effect of alloying elements on the characteristics of intermetallic phases in Zr-containing and Cr-containing 7xxx Al-Zn-Mg-Cu alloys at overaged conditions. Four Al-Zn-Mg-Cu alloy plates with different alloying element contents were studied by optical microscopy based image analysis, differential scanning calorimetry, scanning electron microscopy combined with energy disperse X-ray spectroscopy and transmission electron microscopy. The grain structures, recrystallisation, intermetallic phases and precipitates in the selected alloys have been analysed and the presence of coarse intermetallic phases has been interpreted using established phase diagrams. The different effects of Zr or Cr addition to the alloys have been compared. The experimental results showed that the recrystallised area fraction of Zr-containing alloys is less than that of Cr-containing alloys, being attributable to Zr reducing recrystallisation more effectively than Cr. The detected particles are mainly S phase, Al7Cu2Fe, as well as dispersoids of Al3Zr for Zr-containing alloys and Cr-rich E phase for Cr-containing alloys. These coarse particles, especially the S phase which can not be dissolved during solution treatment, are detrimental to the fracture toughness of the alloys.

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“…pct [43] ) are still present in the equilibrium solid solution during solution treatment at T = 460°C; these amounts of Zr and Sc are retained in the supersaturated solution after water quenching and may affect the kinetics of precipitation of GP zones and g¢ particles during aging. For example, the addition of Zr as a grainrefining element to Al-Zn-Mg alloys has been reported in earlier work [16,17] to retard and suppress the formation of GP zones at RT and, subsequently, to reduce the nucleation of g¢ during artificial aging at 135°C. These negative effects of the Zr additions have been attributed to an increase in the number of vacancy sinks (due to the Zr-induced refined microstructure and the presence of semicoherent or incoherent Al 3 Zr/matrix interfaces) and vacancy traps by Zr solute atoms (due to the high Zr-vacancy-binding energy in aluminum).…”

Section: Discussionmentioning

confidence: 95%

“…[7][8][9][10][11]13] The g¢ precipitates may also nucleate directly from the supersaturated solid solution. The addition of Cu to Al-Zn-Mg alloys has been reported to stabilize the GP zones and g¢ particles (i.e., Cu increases the solvus temperatures and hinders coarsening of these particles) [8,14,15] and suppress formation of the T¢ phase in favor of g. [14] A trace addition of Zr to an Al-5.75Zn-0.74Mg alloy (composition is in weight percent) has been reported in earlier work [16,17] to retard GP zones and g¢ formation and slow down g precipitation. This was attributed to an increase in the number of vacancy sinks and vacancy traps in the wrought microstructure of the Zr-containing alloy.…”

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confidence: 95%

Effect of Sc on Aging Kinetics in a Direct Chill Cast Al-Zn-Mg-Cu Alloy

Senkov

Senkova

Шагиев

2008

Metall Mater Trans A

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The effect of Sc additions on precipitation strengthening in a direct chill (DC) cast Al-Zn-Mg-Cu alloy was studied after natural and artificial aging. The microhardness, room temperature (RT) mechanical properties, and phase composition of the alloys were determined after different steps of aging. The strengthening mechanisms were discussed. It was shown that minor additions of Sc increased the strength of the Al-Zn-Mg-Cu alloy after casting and solution heat treatment, due to the precipitation of fine coherent Al 3 (Sc,Zr) particles. An analysis of the aging kinetics revealed that Sc had no effect on the natural aging, which was controlled by the formation and growth of Guinier-Preston (GP) I zones. On the other hand, the Sc additions accelerated the aging process at 120°C and 150°C within a period of time of the formation and growth of GP II zones and g¢ particles. It was concluded that the presence of Sc accelerated the formation and growth of GP II zones in the Al-Zn-Mg-Cu alloys, which led to the earlier precipitation of the g¢ phase. However, at longer aging times at 120°C and 150°C, the aging response of the Sc-containing alloys slowed down, due to faster coarsening of the g¢ particles and their transformation into g particles. A model of the formation of vacancy-rich clusters (VRCs), precursors to GP zones, in the Al-Zn-Mg-based alloys was proposed. According to this model, the observed effects of Sc on aging are the result of the Sc-induced increase in the number density of the GP II clusters and the concentration of quenched-in solute-bound excess vacancies.

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Role of vacancies on the precipitation processes in Zr modified aluminum based alloys

Cited by 31 publications

References 20 publications

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Identification and analysis of intermetallic phases in overaged Zr-containing and Cr-containing Al–Zn–Mg–Cu alloys

Effect of Sc on Aging Kinetics in a Direct Chill Cast Al-Zn-Mg-Cu Alloy

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