Superplasticity in a thermomechanically processed High-Mg, Al-Mg alloy
- PDF / 2,778,723 Bytes
- 7 Pages / 594 x 774 pts Page_size
- 58 Downloads / 198 Views
I.
INTRODUCTION
SUPERPLASTICITY, originally thought to be confined to a limited number of eutectic and eutectoid composition alloys, ~-4 has now been reported in many systems including even such Al-base alloys as the wrought high-strength alloys 7075 and 7475. 5 Superplastic ductilities in these latter materials are usually reported only at relatively high temperatures (T > 773 K (500 ~ i.e., a temperature above 0.8 Tm) and cavitation is recognized as a problem resulting from deformation by grain boundary sliding. 6'7 Thermomechanical processing methods to attain superplastic behavior in such alloys typically consist of extensive cold or warm rolling followed by recrystallization at temperatures above the solvus temperature for the strengthening phase. Heating to the solvus appears to be necessary to attain sufficient recrystallization to render the material superplastic. Subsequent to such treatment, the elevated temperature ductility is then evaluated by stress-strain testing. Previous work s in this laboratory has demonstrated that high strength with good ductility at ambient temperature is attainable in high-Mg, A1-Mg alloys by a thermomechanical process including warm rolling. The essential features of the thermomechanical processing in that study, applied to an AI- 10.2 pct Mg binary AI-Mg alloy, were solution treatment above the Mg-solvus, accompanied by hot working also above the solvus; quenching through the solvus; reheating to a temperature below the solvus such as 573 K (300 ~ and warm rolling to large strains (Etrue > 2.0, --80 pct reduction). Such a procedure results in a homogeneous, refined, and uniform dispersion of 0.02 to 0.5/zm intermetallic /3 (AlsMgs) in a solid solution matrix comprised of elongated grains containing a refined structure of 0.5 to 1.0/zm-size subgrains. Static annealing below the solvus, e.g., at 573 K (300 ~ resulted in recovery with essentially no reT. R. McNELLEY is Associate Professor, Materials Group, Department of Mechanical Engineering, Naval Postgraduate School, Monterey, CA 93943-5100. E.-W. LEE, formerly in Materials Group, Mechanical Engineering, Naval Postgraduate School, is with the Naval Air Development Center, Warminster, PA 18974. M. E. MILLS, formerly Graduate Student in Mechanical Engineering, Naval Postgraduate School, is with the United States Navy. Manuscript submitted March 25, 1985.
METALLURGICALTRANSACTIONS A
crystallization as revealed by both microscopy and X-ray methods. Maintaining such a uniform dispersion of the intermetallic/9 would be important to the fatigue and especially stress-corrosion characteristics of such a non-heat treatable alloy. Since desirable features of such a structure would be lost upon heating above the solvus to obtain a recrystallized microstructure, it was decided to examine the elevated temperature mechanical behavior in the as-rolled condition. This present work was conducted on an alloy similar to that examined previously, s with the only difference that 0.5 pct Mn was added for further grain refinement. The temperat
Data Loading...
