Enhanced mechanical properties in ultrafine grained 7075 Al alloy
- PDF / 913,568 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 48 Downloads / 225 Views
R.Z. Valiev Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, 450000 Ufa, Russian Federation (Received 22 May 2004; accepted 4 November 2004)
Highest strength for 7075 Al alloy was obtained by combining the equal-channelangular pressing (ECAP) and natural aging processes. The tensile yield strength and ultimate strength of the ECAP processed and naturally aged sample were 103% and 35% higher, respectively, than those of the coarse-grained 7075 Al alloy counterpart. The enhanced strength resulted from high densities of Guinier–Preston (G-P) zones and dislocations. This study shows that severe plastic deformation has the potential to significantly enhance the mechanical properties of precipitate hardening 7000 series Al alloys.
Precipitate strengthening 7000 series Al alloys possess the highest strength among all commercial Al alloys and are widely used for structural applications in military and civil aircraft as well as sporting goods. The 7000 Al alloys are strengthened by a high density of Guinier– Preston (G-P) zones because the strong atomic bonds in the zones can increase the resistance to dislocation movement.1,2 For the Al–Zn–Mg–Cu 7075 system, a high density of G-P zones can be achieved by aging at low temperature (such as room temperature) after solution treatment.3,4 Cold work, which usually improves the strength of metals and alloys, has been found to be ineffective in improving the strength of 7000 series Al alloys. This was explained by the viewpoint that dislocation did not greatly accelerate the G-P zone precipitation.5 In the last decade, cqual-channel-angular pressing (ECAP)6 has been found to enhance mechanical strength significantly by introducing ultrafine grained (UFG) structures into bulk materials. It is of great interest to investigate whether the strengthening effect of the ECAP process can be added to the precipitate strengthening in 7000 series Al alloys. If these two strengthening effects can be made additive, it will be possible to significantly improve the strength of 7000 Al alloys, making them much more attractive in high-strength structural applications. In this work, 7075 Al alloy was selected and processed by combining ECAP and natural aging processes. The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0057 288
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 2, Feb 2005 Downloaded: 14 Mar 2015
results demonstrate that ECAP process can add significant strengthening effect to the precipitate strengthening in 7075 Al alloy. The two strengthening effects were understood from microstructural characteristic of the UFG 7075 Al alloy (G-P zone, grain size, dislocation density and lattice parameter). Commercial 7075 Al alloy, homogenized by solution treatment (at 480 °C for 5 h) and quenched to room temperature, was used immediately for the ECAP process. The sample was pressed through a die for 2 passes with an intersecting channel angle of 90° and an outerarc angle 45° by route Bc. In the Bc rou
Data Loading...
