Origin of superplastic elongation in aluminum alloys produced by mechanical milling
- Tokyo Univ. of Agriculture and Technology, Koganei, Tokyo (Japan). Dept. of Mechanical Systems Engineering
The effects of alloying (Mg, Cu, Ge and/or Si) and prior rolling and annealing on tensile stress-strain behaviors were examined for mechanically milled, powder metallurgy aluminum alloys at 748 K in the strain rate range of 1 {times} 10{sup {minus}4}--7.5 {times} 10{sup 2}/s. Lowering the temperature of prior rolling and increasing the anneal temperature and time result in an increase in the strain rate sensitivity, m. Especially alloying effectively increases the m value as well as the strain to fracture, {var_epsilon}{sub f}, at the intermediate strain rate of approximately 10{sup 0}/s; m and {var_epsilon}{sub f} reach 0.4 and 440% for a case of alloying both 1.1 at.% Mg and 1.2 at.% Cu, though they are smaller than 0.1 and 100% at lower (< 1 {times} 10{sup {minus}2}/s) and higher (> 5 {times} 10{sup 1}/s) strain rates. TEM and SEM revealed that the microstructure of superplastic alloys, compared to pure Al, consists of thermally recovered, fine equiaxed grains (smaller than 1 {micro}m in diameter) with smooth grain boundaries of large misorientation. It is then postulated that superplastic elongation occurs when smooth boundaries slide under a plastically stable condition due to a large m value.
- OSTI ID:
- 302342
- Journal Information:
- Acta Materialia, Vol. 46, Issue 17; Other Information: PBD: 2 Nov 1998
- Country of Publication:
- United States
- Language:
- English
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