MAGNESIUM ALLOY SHEET AND METHOD FOR MANUFACTURING SAME

1 . A magnesium alloy sheet containing 2.7 to 5 wt % of Al, 0.75 to 1 wt % of Zn, 0.1 to 1 wt % of Ca and 1 wt % or less (Excluding 0 wt %) of Mn and consisting of the balance of Mg and inevitable impurities,

wherein the area fraction of the twin structure is 5% or less with respect to 100% of the area of the magnesium alloy sheet.

2 . A magnesium alloy sheet according to claim 1 , containing 0.3 to 0.8 wt % of Ca.

3 . A magnesium alloy sheet according to claim 1 ,

wherein the magnesium alloy sheet comprises Al—Ca secondary phase particles comprising 20 to 25 wt % of Al, 5 to 10 wt % of Ca, 0.1 to 0.5 wt % of Mn, 0.5 to 1 wt % of Zn and the balance of Mg, and wherein the average particle size of the Al—Ca secondary phase particles is 0.01 to 4 μm.

4 . (canceled)

5 . A magnesium alloy sheet according to claim 3 ,

wherein the Al—Ca secondary phase particles comprises 5 to 15 per 100 μm 2 of the magnesium alloy sheet.

6 . A magnesium alloy sheet according to claim 1 ,

wherein the magnesium alloy sheet comprises grains and the average particle size of the grains is 5 to 30 μm.

7 . A magnesium alloy sheet according to claim 1 , wherein the thickness of the magnesium alloy sheet is 0.4 to 2 mm.

8 . A method for manufacturing a magnesium alloy sheet comprising the steps of casting a molten metal containing 2.7 to 5 wt % of Al, 0.75 to 1 wt % of Zn, 0.1 to 1 wt % of Ca and 1 wt % or less (Excluding 0 wt %) of Mn and consisting of the balance of Mg and inevitable impurities to produce a casted material;

subjecting the casted material to homogenization heat treatment; and

warm-rolling the casted material subjected to homogenization treatment.

9 . The method for manufacturing a magnesium alloy sheet of claim 8 ,

wherein the step of producing the casted material, the reduction pressure is 0.2 ton/mm 2 or more.

10 . The method for manufacturing a magnesium alloy sheet of claim 8 , wherein subjecting the casted material to homogenization heat treatment is carried out for 1 to 28 hours at a temperature of 350 to 500° C.

11 . The method for manufacturing a magnesium alloy sheet of claim 8 , wherein warm-rolling is at a temperature of 150 to 350° C., and wherein warm-rolling is performed a plurality of times and rolling is at a reduction ratio of 10% to 30% per time.

12 . (canceled)

13 . The method for manufacturing a magnesium alloy sheet of claim 11 , further comprising the step of one or more times of intermediate annealing in the middle of a plurality of times of warm-rolling, and wherein the intermediate annealing is carried out for 1 to 10 hours at a temperature of 300 to 500° C.

14 . (canceled)

15 . The method for manufacturing a magnesium alloy sheet of claim 8 , further comprising the step of subjecting to subsequent heat treatment after the step of warm-rolling.

16 . (canceled)

17 . A method for manufacturing a magnesium alloy sheet comprising the steps of preparing a master alloy comprising 2.7 wt % or more and 5 wt % or less of Al, 0.75 wt % or more and 1 wt % or less of Zn, 0.1 wt % or more and 1 wt % or less of Ca, more than 0 wt % and 1 wt % or less of Mn and the balance of inevitable impurities and magnesium, for a total of 100 wt %;

casting the master alloy to produce a casted material;

subjecting the casted material to homogenization heat treatment;

warm-rolling the casted material subjected to homogenization heat treatment to produce a rolled material;

subjecting the rolled material to subsequent heat treatment; and

carrying out a skin pass to the rolled material subjected to subsequent heat treatment to produce a magnesium alloy sheet.

18 . The method for manufacturing a magnesium alloy sheet of claim 17 , wherein carrying a skin pass to the rolled material subjected to subsequent heat treatment to produce a magnesium alloy sheet, wherein the skin pass is carried out once, and

wherein the skin pass is carried out at a temperature in the range of 250° C. to 350° C.

19 . (canceled)

20 . The method for manufacturing a magnesium alloy sheet of claim 18 ,

wherein by the step of carrying out a skin pass to the rolled material subjected to subsequent heat treatment to produce a magnesium alloy sheet,

the produced magnesium alloy sheet is rolled at a reduction ratio of 2 to 15% with respect to the thickness of the rolled material.

21 . (canceled)

22 . The method for manufacturing a magnesium alloy sheet of claim 17 ,

wherein the step of subjecting the casted material to homogenization heat treatment comprising

a first heat treatment step at a temperature in the range of 300° C. to 400° C.; and

a second heat treatment step at a temperature in the range of 400° C. to 500° C.

23 . The method for manufacturing a magnesium alloy sheet of claim 22 ,

wherein a first heat treatment step at a temperature in the range of 300° C. to 400° C. is carried out for 5 to 20 hours.

24 . The method for manufacturing a magnesium alloy sheet of claim 23 ,

wherein a second heat treatment step at a temperature in the range of 400° C. to 500° C.

is carried out for 5 to 20 hours.

25 . (canceled)

26 . The method for manufacturing a magnesium alloy sheet of claim 24 ,

wherein by the step of rolling the casted material subjected to homogenization heat treatment to produce a rolled material,

the casted material is rolled 1 to 15 times, and

wherein the step of rolling the casted material subjected to homogenization heat treatment to produce a rolled material

is carried out at 150° C. to 350° C.

27 . (canceled)

28 . The method for manufacturing a magnesium alloy sheet of claim 17 ,

wherein by the step of subjecting the rolled material to subsequent heat treatment, the rolled material is annealed at a temperature in the range of 300° C. to 550° C. is carried out for 1 to 15 hours.

29 - 33 . (canceled)