US EPA

7021178 

Journal Article 

Evolution of the microstructure and mechanisms of formation of new grains upon severe plastic deformation of the 2219 aluminum alloy 

Sitdikov, OS; Kaybyshev, RO; Safarov, IM; Mazurina, IA; , 

2001 

1 

Physics of Metals and Metallography
ISSN: 0031-918X 

INTERPERIODICA 

BIRMINGHAM 

270-280 

WOS:000171699100010 

This work is devoted to the investigation of the microstructure evolution in the 2219 aluminum alloy (Al-6.4% Cu-0.3% Mn-0.18% Cr-0.19% Zr-and 0.06% Fe) upon severe plastic deformation (SPD) in a wide temperature range. Special attention is paid to the mechanisms of formation of new grains. The severe plastic deformation was performed at room temperature by torsion under pressure using Bridgman anvils to a true deformation e = 7. At enhanced temperatures, the alloy was deformed by the equal-channel angular (ECA) pressing to e = 8 at 250 degreesC and e = 12 at 475 degreesC. Based on the data of the optical and electron-microscopic analysis, it was shown that the processes of structure formation in the 2219 alloy at high, intermediate, and room temperatures are different. A specific mechanism of structure formation is observed at room temperature (T approximate to 0.3T(m), where T-m is the melting point of pure aluminum). At the beginning stages of deformation (e = 1), grain fragmentation occurs due to the formation of low-energy dislocation structures (LEDS). Upon the following plastic flow (e = 1-4), new nanograins are formed at the place of these dislocation structures. The forming structure is nonequilibrium because of the high density of grain-boundary defects. The internal elastic stresses decrease upon the following deformation (e > 4) because of the development of recovery at the new grain boundaries. In the intermediate temperature range (T approximate to 0.6T(m)), "continuous" dynamic recrystallization is developed in this alloy. At the beginning stages of plastic flow (e = 1-2), a network of low-angle boundaries is formed inside the initial grains; upon further deformation (e = 2-8), these boundaries gradually transform into random high-angle boundaries. Particles of the second phases play an important role in the formation of new grains. An increase in the deformation temperature to T approximate to 0.75T(m) suppresses continuous dynamic recrystallization. The appearance of new grains in samples deformed to high degrees (e = 8-12) is due to the "geometric" dynamic recrystallization.