Effect of Microstructure on Cavitation during Hot Deformation of a Fine-Grained Aluminum-Magnesium Alloy as Revealed thr
- PDF / 764,613 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 63 Downloads / 151 Views
CTION
SUPERPLASTIC forming (SPF) is a traditional hotforming process for sheet materials that has been widely used in the aerospace and other transportation industries to form components with complex shapes.[1–3] The SPF process utilizes high temperature and gas pressure to form superplastic sheet materials into a die.[2] Quick-plastic forming (QPF), a recent advance in hot-forming technology, improves upon the SPF process by decreasing the forming temperature and increasing the forming rate, thus significantly increasing part production rates for the forming of shapes less complex than those possible with SPF.[4] The QPF process is currently used for the commercial mass production of automobile body closure panels.[4] Finegrained AA5083 sheet material is the most commonly used material for both the SPF and QPF processes. Understanding, predicting, and improving the forming limits of AA5083 sheet materials are critical to advancing QPF and SPF technologies. The forming limits of fine-grained AA5083 sheet materials are controlled by both deformation and failure mechanisms, which depend on temperature, strain rate, and other factors.[5–7] For SPF, grain-boundary-sliding (GBS) creep is widely recognized to be the dominant deformation mechanism in fine-grained AA5083 sheet.[5,8–13] Under GBS creep, the dominant failure JUNG-KUEI ‘‘BRIAN’’ CHANG, Postdoctoral Fellow, and ERIC M. TALEFF, Professor, are with the Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712-0292. Contact e-mail: taleff@mail.utexas.edu PAUL E. KRAJEWSKI, GM Technical Fellow, is with General Motors Corporation, Research and Development, Warren, MI 48090-9055. Manuscript submitted May 13, 2009. Article published online October 27, 2009 3128—VOLUME 40A, DECEMBER 2009
mechanism of AA5083 is cavitation.[6] For QPF, solutedrag (SD) creep begins to dominate deformation as temperature decreases and strain rate increases.[5,6] Under SD creep, cavitation can still lead to failure, but flow localization (e.g., necking) becomes the controlling failure mechanism in some geometries.[6,7] Differences in cavitation evolution with strain, including cavitation growth rate and cavity morphology, have been observed between deformation controlled by GBS creep and deformation controlled by SD creep.[6] However, the initiation strains for cavitation are quite similar between GBS and SD creep deformation,[6] suggesting that cavitation initiates in a similar manner under both deformation mechanisms. Because of its great importance to formabilities, cavitation has been extensively studied in superplastic alloys[14–18] and for AA5083, in particular.[13,19–23] Most investigations documented in the literature used twodimensional (2-D) microstructure data,[13,19–21] and only a few of these investigated cavitation under SD creep. Some work with three-dimensional (3-D) microstructure data is available,[22–24] but data from those investigations do not typically achieve the resolutions of less than approximately 1 lm necessary to distinguish microstru
Data Loading...
