Metal treatment – Compositions – Heat treating
Patent
1983-03-28
1985-07-30
Dean, R.
Metal treatment
Compositions
Heat treating
148 115A, 420902, C22F 104
Patent
active
045319774
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a process for producing superplastic aluminum alloy strips. Particularly, the present invention relates to a process for easily producing superplastic aluminum alloy strips on an industrial scale.
2. Background Art
Metals or alloys which can be elongated to an abnormal extent of hundreds to thousand percents without generating local deformation (necking) when a mechanical force is externally applied thereon have been known as superplastic metals or superplastic alloys. In superplastic aluminum alloys, two types of extra fine recrystallized grains type alloy and fine eutectic structure type alloy are known.
Extra fine recrystallized grains type alloy is obtained by annealing a cold-rolled alloy strip to generate recrystallized grains, where some control measure is taken to make the newly recrystallized grains fine. Also, fine eutectic structure type alloy is obtained by retaining the fine eutectic (mixture phase) structure obtained in the casting step with some control measure to make the structure finer, up to the rolled strip.
In both of superplastic aluminum alloys, the structure thereof consists of extra-fine crystal grains of from 0.5 micrometer or less to a maximum of 10 micrometers in diameter, and the plastic deformation of such a material is easily effected by the smooth grain boundary migration or sliding. In superplastic aluminum alloy of extra fine recrystallized grains type, it is necessary to add specific elements thereinto for preventing the growth of the grains to be larger and coarser. In many cases, transition elements are used as an additive element showing such effect. Further, in the case where a successive deformation is caused to superplastic alloy, a work hardening occurs within the crystal grains and the plastic deformation becomes difficult in time. In order to reduce the tendency of the work hardening, it has also been known to add elements such as copper, magnesium, zinc and the like in addition to the transition elements. Such elements have a function of causing a dynamic recrystallization, that is, a recrystallization which is simultaneously caused with the deformation of the material and constantly regenerates the original structure of the material before deformation.
Formerly, the present inventors have proposed a process for producing aluminum alloy strips of remarkably improved superplasticity, comprising cold rolling the aluminum alloy strips after annealing the aluminum alloy strips produced by continuously casting and rolling a molten aluminum alloy containing magnesium, manganese and chromium (refer to Japanese Patent Application No. 56-36268). Although the process is excellent as a process for producing superplastic aluminum alloy strips, since the aluminum alloy strips cause the work hardening in process of cold rolling, the rolling of the strip gradually becomes difficult with the raise of the reduction ratio.
The present invention provides a method for removing the difficulty caused by this work hardening.
DISCLOSURE OF INVENTION
The characteristic of the present invention is a process for producing strips of superplastic aluminum alloys, comprising continuously casting and rolling a molten aluminum alloy containing 4.0 to 6.0% (by weight) of magnesium, 0.4 to 1.5% (by weight) of manganese, 0.05 to 0.2% (by weight) of chromium and less than 0.50% (by weight) of silicon, thereby obtaining a cast strip of 3 to 20 mm in thickness, after subjecting the thus obtained strip to annealing treatment at a temperature of 420.degree. to 530.degree. C., subjecting the thus treated strip to the former step of cold rolling and the intermediate annealing and subjecting the intermediately annealed strip to the latter step of cold rolling until the reduction ratio reaches to a value of not less than 60%, and the thus produced strip of the aluminum alloy shows an excellent superplasticity at a temperature of higher than 300.degree. C., particularly, at a temperature of higher than 400.degree. C.
BEST MODE OF CARRYIN
REFERENCES:
Metallurgical Transactions A, vol. 6A, Mar. 1975, pp. 591-594.
Metal Science, Jul. 1976, pp. 235-242.
Mishima Ryoji
Miyamoto Hitoshi
Dean R.
Kasei Naoetsu Light Metal Industries, Ltd.
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