Manufacturing method for wide-range fine-grained magnesium alloy thin-sheet material

The present invention relates to a manufacturing method for sheet material, especially to a manufacturing method for wide-range fine-grained magnesium alloy thin-sheet material.

In AZ31 and AZ61 magnesium alloy sheet industry, there are still several difficulties to be overcome. Firstly, in a first processing process of the material from slab to rolling plate, due to coarse grain and segregation of casting slab, it\'s not easy to perform metal plastic rolling processes and thickness reduction ratio of rolling is restricted. Once rolling temperature is increased for improving rollingability, magnesium alloy material is easy to be oxidized so that the surface finish is influenced. Moreover, other problems such as low heat content of magnesium alloy, fast heat dissipation caused by high surface area/volume ratio of the sheet material, and difficulties in uniform temperature of slab/plate are also raised.

Due to hexagonal close packed crystal structure and high work hardening rate of magnesium, the slab needs to be rolled at least over ten passes and gradually eliminating cast structure as well as reducing thickness. Moreover, after the grains being refined, the rolling reduction is increased and surface oxides need to be removed (including turning, grinding and acid cleaning). Then the material is put into a heating furnace and is heated into the rolling temperature for performing next rolling process. There are too many passes of processes for producing magnesium alloy rolled sheet material so that cost of production is quite high. This restricts the applications of magnesium alloy sheet material in various industries.

Furthermore, under the restrictions of hexagonal close packing (hcp) crystal structure of the magnesium alloy, and difficulties in plastic deformation of the magnesium alloy at room temperature, the formability of these rolling sheet is not as good as other cold working sheet material (such as aluminum sheet). Thus there are limits on forming of complicated products.

Forming techniques such as press forging and press forming applied to processing of magnesium foil in industries have got some breakthrough.

For example, Sony Japan Co., Hitachi Metals Co., and Tokyo seitan Co. have develop a new forming technique of thin-walled material. In 2000, Panasonic MD also develops similar technique. These press forging and press forming techniques have advantages of auto-production, high yield rate and superior quality although manufacturing cost of slab rolling processes is still high. In future, once manufacturing cost of magnesium alloy sheet material can be reduced and forming properties of magnesium alloy sheet material can be improved for being applied with press forging and press forming techniques, main stream of magnesium alloy cases produced by magnesium die-casting in 3C (Consumer, Computer and Communication) industries will be changed.

Therefore it is a primary object of the present invention to provide a manufacturing method for wide-range fine-grained magnesium alloy thin-sheet material that combines an extrusion process with a rolling process. By the plastic deformation feature of the two processes, the wide-range fine-grained magnesium alloy thin-sheet material that satisfies the requirement of cases of 3C products with thickness of less than 1 mm is produced.

It is another object of the present invention to provide a manufacturing method for wide-range fine-grained magnesium alloy thin-sheet material that reduces passes of processes of a conventional method so as to reduce the manufacturing cost. Thus the method is able to be applied to various industries.

In order to achieve above objects, a manufacturing method for wide-range fine-grained magnesium alloy thin-sheet material according to the present invention includes a plurality of steps. Firstly, take a magnesium alloy billet. Then, perform an extrusion process. The magnesium alloy billet is extruded through a U-shaped hole of an extrusion die so as to get an U-shaped extruded material. Next, perform a pressing and leveling process. The U-shaped extruded material is pressed and leveled to a wide-range sheet material. Then the wide-range sheet material is rolled into a wide-range thin-sheet material that is further annealed to get a wide-range fine-grained magnesium alloy thin-sheet material.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

FIG. 1 is a flow chart of an embodiment according to the present invention;

FIG. 2 is a cross-sectional view of an extrusion die of an embodiment according to the present invention;

FIG. 3 is a schematic drawing showing a U-shaped extruded material of an embodiment according to the present invention;

FIG. 4 is a schematic drawing showing a pressing and leveling process of an embodiment according to the present invention;

FIG. 5A is a metallographic image of wide-range thin-sheet material of an embodiment according to the present invention;

FIG. 5B is a metallographic image of wide-range fine-grained magnesium alloy thin-sheet material of an embodiment according to the present invention;

FIG. 5C a list of physical and mechanical properties of the wide-range thin-sheet material as well as the wide-range fine-grained magnesium alloy thin-sheet material of an embodiment according to the present invention;

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High-strength hot- rolled steel sheet with excellent combined formability
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Magnesium alloy
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Alloys or metallic compositions

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