Magnesium alloy sheet

Abstract

A magnesium alloy sheet having high impact resistance at low temperature, a magnesium alloy structural member using this sheet, and a method for producing a magnesium alloy sheet are provided. The magnesium alloy sheet is composed of a magnesium alloy containing Al and Mn. When a region from a surface of the alloy sheet to 30% of the thickness of the alloy sheet in a thickness direction of the magnesium alloy sheet is defined as a surface region and when a 50 μm 2 sub-region is arbitrarily selected from this surface region, the number of grains that are crystallized phases containing both Al and Mn is 15 or less. The maximum diameter of each of the crystallized phases is 0.1 to 1 μm and the mass ratio Al/Mn of Al to Mn is 2 to 5. This magnesium alloy sheet has high impact resistance since it contains crystallized phases that are small in size and in amount contained and cause breaking and the like, and exhibits good mechanical properties even in a low-temperature environment.

1 . A magnesium alloy sheet comprising a magnesium alloy containing Al and Mn, wherein when a region from a surface of the alloy sheet to 30% of the thickness of the alloy sheet in a thickness direction of the magnesium alloy sheet is defined as a surface region and when a 50 μm 2  sub-region is arbitrarily selected from this surface region, the number of grains that are crystallized phases containing both Al and Mn an having a maximum diameter of 0.1 to 1 μm is 15 or less, and
 in the grains of the crystallized phases, the mass ratio Al/Mn of Al to Mn is 2 to 5. 
 
     
     
         2 . The magnesium alloy sheet according to  claim 1 , wherein the magnesium alloy contains 5% by mass to 12% by mass of Al and 0.1% by mass to 2.0% by mass of Mn. 
     
     
         3 . The magnesium alloy sheet according to  claim 1  or  2 , wherein the magnesium alloy further contains at least one element selected from Zn, Si, Ca, Sr, Y, Cu, Ag, Ce, Zr, and rare earth elements (excluding Y and Ce). 
     
     
         4 . A magnesium alloy structural member produced by plastic-forming the magnesium alloy sheet according to  claim 1 . 
     
     
         5 . A method for making a magnesium alloy sheet, comprising:
 a casting step of casting a magnesium alloy containing Al and Mn into a sheet,   and   a rolling step of rolling the cast sheet obtained by the casting step,   wherein the casting is conducted by a twin-roll continuous casting process at a roll temperature of 100° C. or less and the thickness of the cast sheet is 5 mm or less.