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

• Published in: Journal of alloys and compounds Vol. 509; no. 2; pp. 471 - 476
• Main Authors: Li, X.M., Starink, M.J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 12-01-2011; Elsevier
• Subjects: Alloys; ALUMINUM ALLOYS (50 TO 99 AL); Aluminum base alloys; Al–Zn–Mg–Cu alloys; Chromium; CHROMIUM ALLOYS (50 TO 99 CR); Chromium base alloys; Cr-containing; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; INTERMETALLIC COMPOUNDS; Intermetallic phases; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; PHASES; Physics; Precipitation; RECRYSTALLIZATION; Zirconium; ZIRCONIUM ALLOYS (50 TO 99 ZR); Zirconium base alloys; Zr-containing; Intermetallic phases; Zr-containing; Cr-containing; Al–Zn–Mg–Cu alloys; Phase diagrams; Intermetallic compounds; Overageing; Optical images; Chromium additions; Structure composition relationship; Zirconium additions; Solution heat treatment; Optical microscopy; Alloying effects; Differential scanning calorimetry; Scanning electron microscopy; Mechanical properties; X-ray spectra; Al-Zn-Mg-Cu alloys; Precipitates; Fracture toughness; Alloying elements; Image analysis; Experimental result; Transmission electron microscopy; Recrystallization; Alloying
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2010.09.064

▶ Intermetallic phases in Zr-containing and Cr-containing Al–Zn–Mg–Cu alloys are analyzed. ▶ The recrystallised area fraction of Zr-containing alloys is less than that of Cr-containing alloys. ▶ The high Cu alloy has the highest volume fraction of coarse particles. ▶ The detected particles are mainly S phase, Al
7Cu
2Fe, as well as Cr, Fe-rich intermetallic particles.
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 analyzed 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, Al
7Cu
2Fe, as well as dispersoids of Al
3Zr for Zr-containing alloys and Cr-rich E phase for Cr-containing alloys. These coarse particles, especially the S phase which cannot be dissolved during solution treatment, are detrimental to the fracture toughness of the alloys.