Method of Manufacturing Cold-rolled Magnesium Alloy Sheet for Improving Formability and Cold-rolled Magnesium Alloy Sheet Having Improved Formability Manufactured thereby

Abstract

A method of manufacturing a cold-rolled magnesium alloy sheet for improving formability, including, (a) preparing a composite sheet which is composed of a main sheet made of magnesium alloy and a restrainer made of steel and functioning to suppress transverse plastic deformation (plastic deformation in a transverse direction) of the main sheet during a rolling process, (b) performing a cold-rolling of the composite sheet, and (c) separating the cold-rolled magnesium alloy sheet from the cold-rolled composite sheet obtained from (b). The magnesium alloy sheets manufactured by the invention has improved formability at an ambient temperature, and thus can be usefully applied to extensive industrial fields such as automobiles and aircrafts.

What is claimed is: 
     
         1 . A method of manufacturing a cold-rolled magnesium alloy sheet for improving formability, comprising:
 (a) preparing a composite sheet which is composed of a main sheet made of magnesium alloy and a restrainer made of steel and functioning to suppress transverse plastic deformation (plastic deformation in a transverse direction) of the main sheet during a rolling process,   (b) performing a cold-rolling of the composite sheet, and   (c) separating the cold-rolled magnesium alloy sheet from the cold-rolled composite sheet obtained from (b).   
     
     
         2 . The method according to  claim 1 , wherein the restrainer includes a groove formed in a side thereof across opposite ends thereof, and the main magnesium alloy sheet is disposed in the groove of the restrainer. 
     
     
         3 . The method according to  claim 2 , wherein both lateral sides of the main magnesium alloy sheet are in contact with mating sides of the groove of the restrainer without gaps therebetween. 
     
     
         4 . The method according to  claim 1 , wherein the main magnesium alloy sheet in (a) is a hot-rolled AZ31 sheet having a composition of Al: 3 weight %, Zn: 1 weight %, Mn: 0.3 weight % and Mg: balance. 
     
     
         5 . The method according to  claim 1 , wherein (b) is performed at a temperature of an ambient temperature −100° C. 
     
     
         6 . The method according to  claim 1 , wherein the main magnesium alloy sheet of the composite sheet is coupled with the restrainer without a gap therebetween. 
     
     
         7 . A cold-rolled magnesium alloy sheet having an improved formability, manufactured by a method according to any one of  claims 1  to  6 . 
     
     
         8 . The cold-rolled magnesium alloy sheet according to  claim 7 , wherein the cold-rolled magnesium alloy sheet has a limit dome height (LDH) which is increased by 20% or more, compared to a magnesium alloy sheet which is not subjected to the cold-rolling process.