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An AA5083 aluminum alloy was modified with two different levels of Cu additions, cast by direct-chill method, and thermo-mechanically processed to sheet gauge. Copper additions reduced sheet grain size, decreased tensile flow stress and significantly increased tensile elongation under most elevated temperature test conditions. The high-Cu (0.8 wt.%) alloy had the finest grain size 5.3 μm, a peak strain-rate sensitivity of 0.6 at a strain-rate of 1 × 10−2 s−1, and tensile elongation values between 259 and 584% over the temperature range, 400-525 °C, and the strain rate range, 5 × 10−4 to 1 × 10−2 s−1, investigated. In biaxial pan forming tests, only the Cu-containing alloys successfully formed pans at the higher strain rate 10−2 s−1. The high-Cu alloy showed the least die-entry thinning. Comparison of ambient temperature mechanical properties in O-temper state showed the high-Cu alloy to have significantly higher yield strength, ultimate strength, and ductility compared to the base 5083 alloy.

Experimental observations show that the continuous cast (CC) Al–Mg alloy with 0.21 wt% Fe has a considerably lower fracture strain than that of a CC alloy with 0.08 wt% Fe and a direct chill cast (DC) alloy with 0.21% Fe. However, the forming limit strains are almost the same for the three alloys. The similarities and differences are thought to relate with the distribution of hard second-phase particles. In the present paper, the influence of particle distribution characteristics (random vs. stringer pattern) and volume fraction (1.2% vs. 3.5%) is examined in detail with the use of a simple plane stress finite element unit cell model. The model permits extension of the composite stress–strain curve beyond the diffuse necking condition so that the nominally uniform response is followed directly by localized necking. The model results agree very well with tensile tests with respect to the differing behaviour of the three materials in the deformation range between the onset of diffuse necking and that for localized necking.

A study has been made on the superplastic deformation behavior of warm-rolled 6013 Al alloy. A series of load relaxation tests have been carried out on a warm-rolled 6013 Al alloy. They are well interpreted by grain boundary sliding (GBS) and grain matrix plastic deformation (GMD) using the internal variable theory of structural superplasticity. Uniaxial tensile testing shows a maximum elongation of 370% achieved at 560 °C under the initial strain rate of 1 × 10−4 s−1. These conditions of maximum elongation are consistent with the load relaxation results.

There is considerable worldwide interest in magnesium (Mg) sheet as a replacement for heavier steel and aluminum alloys in vehicle closure components. As Mg gains acceptance in the automotive industry, there will be an increasing demand for accurate material properties for finite element simulations of Mg structures. In this paper, we investigate the extent to which average grain size and postformed tensile properties vary across a Mg AZ31B hood inner component formed at 485°C for 20 min under a constant gas pressure. Tensile specimens were extracted from six regions of the hood inner, which underwent varying degrees of thinning. A state-of-the-art digital image correlation (DIC) algorithm and custom image acquisition software provided true stress-true strain data for each specimen. Tensile data acquired during room temperature testing was compared with that from baseline (undeformed) Mg AZ31B in a fully recrystallized condition (O-temper). Due to its importance in finite element simulations, particular emphasis was placed on the variation of postformed yield strength with specimen thickness and average grain size. Finally, we compute local strain fields during fracture in a tensile specimen with DIC grids positioned in the failure region.

The laser transformation hardening response of Fe-0.5C-0.8Mn and Fe-0.5C-0.8Mn-0.8Cr steels was examined. A 2 kW CO2 laser was used to scan the steel surfaces at various rates. Complete transformation of pearlite to austenite, and hence to martensite, occurred in the laser heated surface layer of the Fe-C-Mn steel. During equivalent heat treatment of the Fe-C-Mn-Cr steel, incomplete austenitization of the pearlite colonies left the cementite plates largely undissolved. However, the maximum surface hardness was approximately the same for both alloys. Comparison of calculated and measured hardened depths yielded values of the effective coupling coefficient of the laser beam to the steel which varied as a function of beam interaction time. Modeling the process allowed a dis-tinction to be made between the effects of alloying elements and of pearlite spacing upon the depth of complete austenitization. In this case, the effect of the difference in pearlite spacing between the two steels was negligible. In the alloy steel, Cr and Mn were strongly partitioned to the cementite before heat treatment, and remained so after laser processing. Incomplete austenitization of that steel is attributed to partitioning of alloying elements to the cementite and their retarding influence on the diffusion controlled dissolution kinetics of the alloyed carbide.

Successful laser transformation hardening of steel surfaces requires that the absorbed laser energy is sufficient to austenitize the initial microstructure to a depth of 0.5 mm or more. Hardening is accomplished when rapid cooling by conduction of heat away from the surface causes transformation of the austenite layer to martensite. Heating and cooling rates of 10/sup 4/ K/s or greater are typical of the laser hardening process and the entire thermal cycle may be accomplished in less than 0.1 s. In an earlier study, laser surface hardening of commercial plain carbon and chromium alloyed steels was examined. It was shown that in the alloyed steel chromium enrichment of the cementite in the initial microstructure could prevent complete transformation of pearlite to asutenite during the very rapid laser heating cycle. However, interpretation of the results was complicated somewhat by the fact that manganese was also partitioned to the cementite. The purpose of this work was to conduct selected identical laser heating experiments on a high-purity Fe-C-Cr alloy to test the effect of chromium unequivocally, i.e., in the absence of manganese and other elements normally present in commercial steels.

Electron probe microanalysis (EPMA) and analytical electron microscopy (AEM) were used to characterize the changes that occur on a vehicle-aged three-way automotive catalyst as a result of two rejuvenation treatments. One treatment involves washing a catalyst with an aqueous solution of oxalic acid followed by calcination. This treatment results in the redistribution of phosphorus- and lead-based poison deposits, but leaves silicon- and sulfur-containing species in place. Noble metal radial profiles within the catalyst appear to be unaffected. Some evidence was found that this washing treatment may reverse the segregation of Pd in multimetallic Pt/Pd particles. The second treatment involves the redispersion of the noble metals by a high-temperature chlorination. This process has little effect on poison or noble metal radial distributions within the catalyst pellet. However, substantial reduction in the noble metal particle size was observed; particle size distributions which are comparable to those observed on fresh catalysts were produced by this treatment. The redispersed noble metal particles were generally multimetallic, indicating little bulk separation of the noble metals from the multimetallic particles originally present on the aged catalyst.

The microscopic details of fresh and vehicle-aged commercial pelleted automotive exhaust catalysts containing Pt, Pd and Rh were studied by employing analytical electron microscopy (AEM). Two different vehicle-aged samples containing similar poison levels but having different catalytic activities (denoted better and poorer) were selected for this study. The general microstructure of the supports and the noble metal particles of the two aged catalysts were found to be similar but the average noble metal particle size on the poorer catalyst (21 nm) was larger than that on the better catalyst (16 nm). These sizes represent a significant increase in particle size over that found on the fresh catalyst (8 nm). The activity of these catalysts decreases as the observed particle size increases. The fresh and better catalyst had a more uniform distribution of particle sizes over the full depth of the pellet impregnation zone while the particle size on the poorer catalyst increased significantly with depth. Nearly all the noble metal particles observed on both the fresh and the two aged catalysts were bi-or trimetallic. For each catalyst, the particle composition was a function of radial position. This radial dependence of composition is a result of the different impregnation profiles of the individual noble metals which were determined by electron probe microanalysis (EPMA). The larger Pt/Pd bimetallic particles on the better catalyst were homogeneous with little, if any, Pd enrichment of the surface. Such particles on the poorer catalyst exhibited non-uniform surface and bulk distribution of Pt and Pd. For all catalysts, the presence of Rh was readily detected by EPMA but was difficult to find in the observable noble metal particles. For both catalysts, the major poison deposits were concentrated in a zone less than 10 μm deep. Major contaminants were P, Pb, Zn, Ca and Si which were present as dense, noncrystalline deposits, often appearing as a shell covering the surface of the catalyst pellet. These observations support the pore mouth blockage model of poisoning. No information concerning the presence of poisons on the surfaces of noble metal particles was obtained.