ECAP‐Umformung mittel‐ und hochfester ausscheidungshärtbarer Aluminiumknetlegierungen

Abstract

The study deals with the optimisation of medium-to highstrength aluminium wrought alloys. The goal is to define processing routes in order to improve the mechanical properties if compared to their commercial counterparts. It is shown for the Al-Mg-Si and the Al-Cu-Mg-Si system that the application of ECAP enables a significant increase in strength. The strengthening as well as the grain size reduction respectively, benefit from increasing alloying as well as from the degree of aging. It is also shown that the presence of a considerably fine particulate reinforcement hardens the material tremendously during ECAP. The combination of a pre-or post-ECAP heat treatment enables the improvement of the workability on the one hand, reducing the loads on the die, and also gives a better ductility on the other hand. This positive effect is particularly pronounced for low alloying contents and high aging temperatures and can be attributed to the interaction of deformation induced defects and the precipitation activity. The combination of an appropriate set of ECAP parameters (heat treatment condition, ECAPstrain, -temperature, -backpressure) enables the efficient production of outstanding properties. Due to the low workability of AA7075 (Al-Zn-Mg-Cu system) no significant improvement in properties was achieved.

The effect of anodic oxide coating on the fatigue behaviour of AA6082 with an ultrafine‐grained microstructure

“…Both conditions have a moderate ductility with a uniform elongation of 5 %. For the ultrafine-grained material, this implies a significant enhancement, since the as-processed (non-optimised) material shows a uniform elongation of less than 1 % after two passes [8]. Using low-voltage scanning transmission electron microscopy, the grain size of the ECAP-processed condition was determined to be in the submicron range.…”

“…To overcome the impairment in ductility, which results from the work hardening, a combined treatment of ECAP and aging has been proposed for aluminium alloys. This optimisation method facilitates the production of material conditions with both elevated strength and moderate ductility for medium-to high-strength aluminium alloys [7][8][9].…”

Effect of Creep and Aging on the Precipitation Kinetics of an Al–Cu Alloy after One Pass of ECAP

“…Sklenicka et al [7] observed similar results for compression creep tests after ECAP of different aluminum alloys. According to ref., [22] an evolution of the precipitates during creep testing obscures the secondary creep stage. We also note that the creep curves of all loads at 200 C ( Figure 3a) indicate considerably shorter creep lives compared to the initial condition.…”

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

“…Der Werkstoff versagt makroskopisch spröde ohne einzuschnü-ren. Die im Vergleich zum unverstärkten Material [20] deutlich geminderten mechanischen Eigenschaften sind offensichtlich vorwiegend auf die nachgewiesene Porosität zurückzuführen, der durch die Partikelverstärkung eigentlich erwartete Verfestigungseffekt bleibt aus.…”

“…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).…”