On microsuperplasticity in aa7475 domes
- PDF / 2,185,313 Bytes
- 4 Pages / 597.28 x 777.28 pts Page_size
- 72 Downloads / 168 Views
On Microsuperplasticity in AA7475 Domes M.G. ZELIN Formation of thin fibers has been observed in a number of aluminum alloys deformed at elevated temperat~Jres, particularly under superplastic conditions. I~-7~ Such threadlike fibers were found at the failure surfacet~-SJ as well as the
M.G. ZELIN, formerly Post Doctoral Researcher with the Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616-5294, is Senior Engineer, Concurrent Technologies Corporation, Johnstown, PA 15904. Manuscript submitted October 24, 1995.
deformed surface of unfailed materials, t6,71 Since the appearance of these fibers suggests extremely high ductility of the material, the process of fiber formation has been referred to as microsuperplasticity phenomenon.tJ,z.31 Predominately, the observations of microsuperplasticity phenomenon were reported in materials subjected to the uniaxial tension. Recent s t u d y [8'91 of the deformed surface of superplastically bulged AA7475 domes demonstrated fiber formation after biaxial stretching. This article summarizes the results of the observation of fiber formation in AA7475 domes of various shapes. AA7475 blanks, 50 X 50 x 1.5 mm 3 were bulged with the punches of hemispherical, cylindrical, and conical shape. The experimental details can be found elsewhere.[8,9~ Superplastic AA7475 sheet material with a grain size of approximately 10/~m was obtained from Kaiser Aluminum and Chemical Co. (Pleasanton, CA). The rate of punch displacement and temperature corresponded to the optimum strain rate-temperature conditions for this alloy:f6,7,1~ l] ~: = 2 x 10 4 S-I and T = 516 ~ The blanks were mechanically polished before deformation with the final polishing on alumina with 0.5 /xm particle size. Marker lines were inscribed at the polished surface by using 9/~m diamond paste parallel and perpendicular to the rolling direction. The deformed surface was examined in a scanning electron microscope (SEM). Chemical analysis was performed by us-
Fig. l~-(a) Deformed surface of superplastically stretched AA7475 conical dome. (b) and (c) Fibers formed at grain boundaries surrounding grain groups which slid as an entity (offset of marker lines indicated by arrows). SEM. T = 516C,~ = 2 x 10 4 s L 1400--VOLUME 27A, MAY 1996
METALLURGICAL AND MATERIALS TRANSACTIONSA
Fig. 2 - - A montage of SEM micrographs taken from the deformed surface of superplastically stretched AA7475 hemispherical dome. Sliding grain blocks surrounded by boundaries decorated by fibers are seen. SEM, T = 516C, t~ = 2 x 10-4 s -~.
ing energy-dispersive X-ray analysis; the beam spot resolution was 1 /xm. Figure l(a) shows the deformed surface in a top region of a superplastically bulged conical dome. Groups of grains which slid as an entity are seen. A significant offset of marker lines is seen at the grain boundaries surrounding the sliding grain groups (for example, indicated by arrows). The marker lines are still unbroken inside the sliding grain groups. Thin fibers decorate these surfaces of cooper
Data Loading...
