Formed product of magnesium alloy and magnesium alloy sheet

Abstract

A formed product of a magnesium alloy having excellent impact resistance and a magnesium alloy sheet suitable as a material for the formed product are provided. The formed product is produced by press-forming a magnesium alloy sheet having an Al content of 7% by mass to 12% by mass and has a flat portion that is not subjected to drawing deformation. In a metal texture in a cross section of the flat portion in the thickness direction, the number of coarse intermetallic compound (Mg 17 Al 12 ) particles having a particle size of 5 μm or more present in a surface area region extending from a surface of the flat portion to a position one-third of the thickness from the surface in the thickness direction is five or less. The formed product has a texture in which the number of coarse precipitations d 1 is small and in which fine precipitations d 0 are dispersed. The formed product is less likely to be dented even when impacted because of dispersion strengthening owing to the fine precipitations and solid-solution strengthening owing to Al that sufficiently forms a solid solution.

1 - 9 . (canceled) 
     
     
         10 . A formed product of a magnesium alloy produced by press-forming a sheet composed of a magnesium alloy,
 wherein the magnesium alloy contains 7% by mass to 12% by mass Al,   the formed product has a flat portion that is not subjected to drawing deformation, and   wherein in the case where in a metal texture in a cross section of the flat portion in the thickness direction, a region extending from a surface of the flat portion to a position one-third of the thickness from the surface in the thickness direction is defined as a surface area region, two 100 μm×100 μm areas in the surface area region are set to fields of observation, and where particles composed of an intermetallic compound containing Al and Mg and each having a particle size of 5 μm or more are defined as coarse particles,   the number of the coarse particles present in each of the fields of observation is five or less.   
     
     
         11 . The formed product of a magnesium alloy according to  claim 10 , wherein when the following dent test of a 30 mm×30 mm specimen with a thickness of t p  cut from the flat portion is performed, the depth x p  of the dent of the specimen meets the expression x p ≦0.47×t p   −1.25 :
 (Dent Test)
 The specimen is arranged on a support having an opening with a diameter of 20 mm so as to close the hole; in this state, a cylindrical bar having a weight of 100 g and a tip radius r of 5 mm is allowed to free fall from a position 200 mm above the specimen; and 
 wherein the depth x p  of the dent is defined as a distance between a straight line that connects both sides of the specimen and the most dented point after the dent test. 
 
 
     
     
         12 . The formed product of a magnesium alloy according to  claim 10 , wherein the magnesium alloy contains at least one element selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, and rare-earth elements (except Y). 
     
     
         13 . The formed product of a magnesium alloy according to  claim 11 , wherein the magnesium alloy contains at least one element selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, and rare-earth elements (except Y). 
     
     
         14 . The formed product of a magnesium alloy according to  claim 12 , wherein the magnesium alloy contains, on a mass percent basis, 8.3%-9.5% Al and 0.5%-1.5% Zn. 
     
     
         15 . The formed product of a magnesium alloy according to  claim 13 , wherein the magnesium alloy contains, on a mass percent basis, 8.3%-9.5% Al and 0.5%-1.5% Zn. 
     
     
         16 . The formed product of a magnesium alloy according to  claim 14 , wherein a corrosion prevention layer is formed by chemical-conversion treatment on a surface of the sheet of the magnesium alloy. 
     
     
         17 . The formed product of a magnesium alloy according to  claim 15 , wherein a corrosion prevention layer is formed by chemical-conversion treatment on a surface of the sheet of the magnesium alloy. 
     
     
         18 . A magnesium alloy sheet used for press forming,
 wherein the magnesium alloy contains 7% by mass to 12% by mass Al, and   wherein in the case where in a metal texture in a cross section of the sheet in the thickness direction, a region extending from a surface of the sheet to a position one-third of the thickness from the surface in the thickness direction is defined as a surface area region, two 100 μm×100 μm areas in the surface area region are set to fields of observation, and where particles composed of an intermetallic compound containing Al and Mg and each having a particle size of 5 μM or more are defined as coarse particles,   the number of the coarse particles present in each of the fields of observation is five or less.   
     
     
         19 . The magnesium alloy sheet according to  claim 18 , wherein when the following dent test of a 30 mm×30 mm specimen with a thickness of t b  cut from the sheet is performed, the depth x b  of the dent of the specimen meets the expression x b ≦0.47×t b   −1.25 :
 (Dent Test)
 The specimen is arranged on a support having an opening with a diameter of 20 mm so as to close the hole; in this state, a cylindrical bar having a weight of 100 g and a tip radius r of 5 mm is allowed to free fall from a position 200 mm above the specimen; and 
 wherein the depth x b  of the dent is defined as a distance between a straight line that connects both sides of the specimen and the most dented point after the dent test. 
 
 
     
     
         20 . The magnesium alloy sheet according to  claim 18 , wherein the magnesium alloy contains at least one element selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, and rare-earth elements (except Y). 
     
     
         21 . The magnesium alloy sheet according to  claim 19 , wherein the magnesium alloy contains at least one element selected from Zn, Mn, Si, Ca, Sr, Y, Cu, Ag, and rare-earth elements (except Y). 
     
     
         22 . The magnesium alloy sheet according to  claim 20 , wherein the magnesium alloy contains, on a mass percent basis, 8.3%-9.5% Al and 0.5%-1.5% Zn. 
     
     
         23 . The magnesium alloy sheet according to  claim 21 , wherein the magnesium alloy contains, on a mass percent basis, 8.3%-9.5% Al and 0.5%-1.5% Zn. 
     
     
         24 . A method for producing a formed product of a magnesium alloy by subjecting a sheet composed of a magnesium alloy to press forming, the method comprising:
 a preparation step of preparing a cast sheet composed of a magnesium alloy having an Al content of 7% to 12% by mass and produced by a continuous casting process;   a solution heat treatment step of subjecting the cast sheet to solution heat treatment at 350° C. or higher;   a rolling step of subjecting the sheet material that has been subjected to the solution heat treatment to rolling; and   a press-forming step of subjecting the rolled sheet obtained in the rolling step to press forming,   wherein in a cooling substep from the holding temperature of the solution heat treatment in the solution heat treatment step, the cooling rate is 0.1° C./sec or more in a temperature range of 350° C. to 250° C.,   in the rolling step, the total time that the sheet material, which is a workpiece, is held in a temperature range of 250° C. to 350° C. is within 60 minutes, and   in the press-forming step, the press forming is performed in a temperature range of 200° C. to 300° C.   
     
     
         25 . A method for producing a magnesium alloy sheet composed of a magnesium alloy, the magnesium alloy sheet being used for press forming, the method comprising:
 a preparation step of preparing a cast sheet composed of a magnesium alloy having an Al content of 7% to 12% by mass and produced by a continuous casting process;   a solution heat treatment step of subjecting the cast sheet to solution heat treatment at 350° C. or higher; and   a rolling step of subjecting the sheet material that has been subjected to the solution heat treatment to rolling,   wherein in a cooling substep from the holding temperature of the solution heat treatment in the solution heat treatment step, the cooling rate is 0.1° C./sec or more in a temperature range of 350° C. to 250° C., and   in the rolling step, the total time that the sheet material, which is a workpiece, is held in a temperature range of 250° C. to 350° C. is within 60 minutes.