Deformation and failure of a superplastic AA5083 aluminum material with a cu addition

Abstract

A modified AA5083 aluminum sheet material containing a Cu addition of 0.61 wt pct has been investigated under conditions relevant to commercial hot-forming technologies. This material was produced by continuous casting followed by industrial hot and cold rolling into sheet. Deformation and failure mechanisms at elevated temperatures were investigated through mechanical testing, thermal analysis, and microscopy. The effects of Cu addition are evaluated by comparisons with data from AA5083 sheet materials without Cu addition, produced both by continuous and direct-chill (DC) casting techniques. At low temperatures and fast strain rates, for which solute-drag (SD) creep governs deformation, the Cu addition slightly increases tensile ductility at 450°C but does not otherwise alter deformation behaviors. At high temperatures and slow strain rates, for which grainboundary-sliding (GBS) creep governs deformation, the Cu addition decreases flow stress and, at 450°C, improves tensile ductility. A strong temperature dependence for tensile ductility results from the Cu addition; tensile ductility at 500°C is notably reduced from that at 450°C. The Cu addition creates platelike particles at grain boundaries, which produce incipient melting and the observed mechanical behavior.

Characteristics of the Transition from Grain-Boundary Sliding to Solute Drag Creep in Superplastic AA5083

“…Furthermore, plasticity-controlled cavity growth models [50,52] neglect the role of constituent particles in processes of cavitation growth. [8,40] Altogether, these results confirm previous work indicating that there is a transition from GBS to SDC and an accompanying transition in failure mechanism during deformation in the QPF regime. Then, the tensile ductility during deformation in this regime reflects a balance of cavitation growth and flow localization.…”

“…[3,5] During QPF, deformation takes place in a regime of strain rate and temperature in which both GBS and solute drag creep (SDC) contribute together. [6][7][8] For the deformation of Al-Mg alloys such as AA5083 in the combined GBS and SDC regime, values of the strain-rate sensitivity coefficient, m d log r=d log _ e, of 0.25 through 0.33 were reported, where r is the true flow stress and _ e is the true strain rate. [6] In general, slip creep processes involving diffusion-controlled dislocation climb in coarse-grained polycrystalline materials give m ' 0:2 [9,10] and ductility 100 pct.…”

Friction stir processing (FSP) and superplasticity

“…The introduction of continuously cast (CC) AA5083 would help reduce costs but as-cast CC slab is typically only 15 mm in thickness and thus cannot be strained sufficiently during hot and cold working to homogenize as well as refine microstructure in the production of sheet material. Thus, subsequent ductility is marginal for SPF and QPF [30][31][32]. The potential of FSP to homogenize and refine microstructure suggests that its application to CC material be evaluated to determine whether the resulting microstructures exhibit improved superplastic response.…”

“…The potential of FSP to homogenize and refine microstructure suggests that its application to CC material be evaluated to determine whether the resulting microstructures exhibit improved superplastic response. The CC AA5083 material was in the form of 15 mm thick slab and further details have been given previously [30,32]. Composition data are given in Table 1. A plate for FSP was sectioned from the as-cast CC material and surfaces were machined prior to processing.…”

Friction Stir Processing (FSP) of Cast Metals: Microstructure – Property Relationships in NiAl Bronze and AA5083

“…Test results for a series of five tests on the FS'ed material are compared in Fig. 7 to tests of conventional AA5083 produced by direct-chill casting and hot and cold rolling to 1.4mm thickness, and continuously cast AA5083 after conventional hot and cold rolling to the same thickness [11][12][13][14]. FSP has resulted in a reduction in flow stress and increase in strain rate for the maximum value of the strain rate sensitivity coefficient,…”