On through thickness crystallographic texture gradient in Al-Li-Cu-Zr alloy
- PDF / 221,318 Bytes
- 2 Pages / 613 x 788.28 pts Page_size
- 31 Downloads / 166 Views
13.
-- ~ 540 - 2090 a / .=_ f-
,oj ' ~"o 460
A. K. VASUDI~VAN, W. G. FRICKE, Jr., R.C. MALCOLM, R.J. BUCCI, M.A. PRZYSTUPA, and E BARLAT It has been observed ]-~ that commercial A1-Li-Cu-Zr and A1-Li-Cu-Mg-Zr type alloys exhibit pronounced yield stress anisotropy in sheet, plate, and extruded products. In thin sheets where the texture is more or less uniform through the thickness, the yield stress varies with angle of the tensile axis to the rolling direction. In case of thick plates (or thick extrusions), there is a possible additional anisotropy because the texture and the microstructure vary through the thickness. Historically, the major cause of yield strength anisotropy has been attributed to th e crystallographic texture. The objective of the present study was to use the variation of the crystallographic texture through the thickness of a plate as a tool in separating the crystal orientation effect from the microstructural effect. Obviously, all locations in a plate have seen similar time-temperature cycles. Preliminary results indicate that the through-thickness yield strength variation in the 2090 alloy is, in part, related to the crystallographic texture, but other factors are also important. The alloy under study was laboratory-produced 2090 (A12.2Li-2.8Cu-0.12Zr, in wt pct) in the form of 12.7 mm plate. The plate was solution heat treated, stretched, and aged to T8E41 (peak aged) temper. Tensile samples (1 mm thick) were machined from various depths in the plate with their long axes along the longitudinal direction (0 deg to the rolling direction). Yield strength was determined at 0.2 pct offset strain at room temperature. The crystallographic texture was obtained at those same depth locations using X-ray Orientation Distribution Function (ODF) analysis. The ODF results were then used to calculate the Taylor factor 'M', for a tensile stress along the longitudinal direction, assuming full constraints. 5'6 The longitudinal yield strength increased from low values at the surfaces to a maximum at the mid-thickness of the plate (Figure l(a)). The strength of the crystallographic texture changed in a similar manner (Figure l(b)). In general, the components of the hot rolling texture (Brass, S, and Copper) increased to a maximum value at the mid-thickness of the plate while the components associated with a recrystallization texture (Cube and Goss) had the opposite trend. In particular, the brass component (110) [ 1]2] showed a pronounced effect. Figure 1 immediately suggests that there is a correlation between the crystallographic texture variation and yield strength. The variation in brass component alone through the thickness is very similar to that for the yield strength. It is also noted that near the top and A.K. VASUDI~VAN, Staff Scientist, W.G. FRICKE, Jr., Senior Scientific Associate, R.C. MALCOLM, Senior Technologist Analyst, and R. J. BUCCI, Senior Technical Specialist, are with Aluminum Company of America, ALCOA Labs., Alcoa Center, PA 15069. M. A. PRZYSTUPA is Consultant, P.O. Box 39, Redondo Bea
Data Loading...
