Mechanical properties of an Al-Zn-Mg alloy processed by ECAP and heat treatments

Abstract

An investigation was conducted to study the influence of equal-channel angular pressing (ECAP) and post-ECAP aging at 393 K for 20 h on the microstructures and tensile properties of a supersaturated Al-Zn-Mg alloy together with the effect of pre-ECAP heat treatments on the mechanical properties of the alloy after ECAP and after post-ECAP heat treatments. The results show that during ECAP processing for up to 4 passes for the supersaturated Al alloy there is a simultaneous occurrence of grain refinement, increases in the dislocation density and dynamic aging precipitation forming large numbers of fine spherical well-distributed precipitates which enhance the yield strength but decrease the ductility. During post-ECAP aging, there is a limited dislocation recovery with slight grain growth and the precipitate sizes increase together with the formation of a few larger platelet precipitates and the transformation of G.P. zones to η' and η' to η leading to a strength reduction after 4 passes of ECAP. The precipitates in the ECAP-processed alloy with pre-ECAP in the supersaturated state formed through dynamic aging precipitation are higher in their volume fraction, smaller in their size and more homogeneously distributed in the Al matrix than those in the alloy with pre-ECAP in the peak aging state which mainly come from the fragmented η' existing in the matrix before ECAP. The strengths of the alloy both after ECAP processing and after post-ECAP heat treatments with pre-ECAP in the supersaturation state are higher than with pre-ECAP in the peak aging state.

Promoted Anodizing Reaction and Enhanced Coating Performance of Al–11Si Alloy: The Role of an Equal-Channel-Angular-Pressed Substrate

“…Figure 16a shows a typical TEM micrograph of the Al phase in the ECAPed alloy, where a grain with a size of about 2 μm can be found. As reported in many ECAPed materials, the formation of such fine grains is caused by the continuous evolution of dislocations, from discrete dislocations to tangles, cells, walls, and eventually sub-grain boundaries or new grain boundaries, to achieve grain refinement caused by the sufficient imposition of strain [56,57,58]. It should be noted that due to the relatively high ECAP executive temperature (648 K), the dynamic recovery and recrystallization is presumably concurrent during the ECAP process.…”

Effect of Ultrafine Grains on the Coating Reaction and Anticorrosion Performance of Anodized Pure Aluminum

“…As generally believed, the formation of UFGs in many ECAP-processed metals results from the continuous evolution of dislocations. Sufficient input strain stimulates the discrete dislocations to form tangles, cells, walls, subgrain boundaries, and grain boundaries to finally achieve dramatic grain refinement [51][52][53][54]. Because of the high stacking-fault energy of the Al crystals, dynamic recrystallization readily occurs in the deformed Al matrix, leading to low intragranular dislocation density and restricted grain refinement [55,56].…”

Deformation Behavior and Microstructural Evolution of T-Shape Upsetting Test in Ultrafine-Grained Pure Copper

“…Studies have shown that the above-mentioned drawbacks can be significantly ameliorated when using ultrafine-grained materials [5,6], which paves the way for the development of micro-forming technology. To date, such techniques as equal-channel angular pressing (ECAP) [7][8][9], high-pressure torsion (HPT) [10] and other methods have been developed to refine the grains to micron and submicron grains of intense plastic deformation severe plastic deformation (SPD) techniques. Among them, ECAP processing is considered to be the most promising method with bulk three-dimensional isometric grains UFG material preparation.…”