Combining Equal-Channel Angular Extrusion (ECAE) and Heat Treatment for Achieving High Strength and Moderate Ductility in an Al-Cu Alloy

Abstract

Abstract. The effect of equal-channel angular extrusion (ECAE) on mechanical properties of an AA2017 produced by powder metallurgy is investigated. Special attention is given to the influence of heat treatment, processing temperature and backpressure on the workability for achieving high strength and moderate ductility. This is of special interest, since it is often reported that Al-Cu alloys have low ductility and therefore are prone to cracking during severe plastic deformation. It is shown that ECAE at high temperatures (>220°C) does not necessitate backpressure to ensure homogeneous deformation but leads to a significant sacrifice in strength due to in-situ precipitation. Thus, most of the extrusions are done at considerably low temperatures. Performing room temperature-extrusion is most effective in achieving high strengths but also requires high backpressures. Due to severe strain hardening during processing, the strength increase is combined with a reduction in ductility. Recently it was reported that a post-ECAE aging of pre-ECAE solution treated material is effective in enhancing the ductility of aluminium alloys. This approach was successfully transferred to the current alloy. A high-temperature, short-time aging after only one extrusion, for example, doubles the failure strain to a value of ~13%. Compared to the naturally aged condition with coarse grains that serves as reference (T4), an increase of 15 % in yield stress (YS) was obtained while retaining the ultimate tensile stress (UTS). Another effective approach is the combination of a pre-ECAE solution treatment with subsequent under-aging prior to ECAE. It is shown that performing ECAE at medium temperatures (160-180°C) enables a better workability and additionally gives higher strengths and better ductility compared to the processing in the water quenched condition. A remarkable YS of 530 MPa and an UTS of 580 MPa combined with a moderate failure strain of 11.6 % were achieved.

Particle Based Alloying by Accumulative Roll Bonding in the System Al-Cu

“…This was already observed for Al-Cu alloys during equal channel angular pressing (ECAP), where backpressure and/or elevated temperatures were necessary to avoid cracking in AA2024 [15] and AA2124 [16]. However, here by ARB processing at room temperature approximately the same strength of AA2017 is reached before damage of the material occurs by further deformation as by ECAP with backpressure at room temperature [17]. The very high strength achieved by severe plastic deformation of Al-Cu alloys demonstrates their high potential for lightweight applications.…”

Effect of ECAP and heat treatment on microstructure and mechanical properties of a SiC reinforced Al‐Cu alloy

“…Die hohe Versetzungs-und Korngrenzendichte, die bei ECAP-Materialien durch die starke Scherverformung eingebracht wird, erschwert die Versetzungsbewegung und trägt somit entscheidend zur Verfestigung des Werkstoffes bei [2, 16, 26 -28]. Der Rückgang der Verformungsfähigkeit ist typisch für ECAP umgeformte Werkstoffe ohne nachgelagerte Stabilisierung [2,18,20]. Bei der Betrachtung der Bruchfläche der ECAPierten Probe ist ein Mischbruch mit vorwiegend dukti- lem Anteil zu erkennen (Bild 6).…”

Effect of SiC‐Reinforcement and Equal‐Channel Angular Pressing on Microstructure and Mechanical Properties of AA2017

“…For instance, coarse brittle phases can form during melting. Moreover, because of the lower temperatures used in the powder route, chemical reactions between matrix and reinforcements are reduced to a minimum 4–7…”

“…Despite the potential of ECAP processing of AMCs, such processing techniques have hardly been investigated so far; most ECAP studies were performed on pure metals and their alloys 11–15. Only a limited number of reports deals with ECAP of AMCs,8–10, 16–18 mainly because such difficult‐to‐work materials are prone to form shear localizations or cracks 4. To the best of our knowledge, almost no studies on ECAP of powder metallurgical SiC‐reinforced AA2017 have been published before 19.…”

“…To the best of our knowledge, almost no studies on ECAP of powder metallurgical SiC‐reinforced AA2017 have been published before 19. A detailed analysis of the effect of ECAP on the mechanical behavior of the Al–Cu alloy without reinforcement has been published in ref 4…”