Apparatus and method of producing a fine grained metal sheet for forming net-shape components

Abstract

A method and apparatus for producing ultra-fine grained magnesium metal alloy material sheets. The apparatus molds and rapidly solidifies a metal alloy material to form a fine grain precursor. The precursor is then subjected to deformation strains that alter the grain structure of the precursor so as to form a ultra fine grained structure in sheet form. The sheet form may then be subjected to superplastic forming to form a net shaped article.

1 . A method of forming a sheet material having a refined grain structure, the method comprising: 
 providing a magnesium metal alloy material;    molding and rapidly solidifying the metal alloy material to form a fine grain precursor, wherein molding includes substantially melting the metal alloy material; and    imparting plastic deformation to the fine grain precursor by a deformation strain to form an ultra fine grain structured sheet form.    
     
     
         2 . The method of  claim 1  wherein the fine grain precursor has an isotropic grain structure.  
     
     
         3 . The method of  claim 1  wherein the step of providing the magnesium metal alloy material and the step of molding and rapidly solidifying are repeated to form a plurality of fine grain precursors and the method further comprises stacking the plurality of fine grain precursors to form a stack and the step of imparting plastic deformation includes plastically deforming the stack by the deformation strain.  
     
     
         4 . The method of  claim 3  wherein a ratio of a thickness of the stack to a thickness of the ultra fine grain structured sheet form is in the range of approximately 3:1 to 30:1.  
     
     
         5 . The method of  claim 3  wherein a ratio of a plan view area of the ultra fine grain structured sheet form to a plan view area of the stack is in the range of approximately 3:1 to 30:1.  
     
     
         6 . The method of  claim 3  wherein the step of imparting plastic deformation bonds the fine grain precursors together to form the ultra fine grain structured sheet form.  
     
     
         7 . The method of  claim 3  wherein at least two of the fine grain precursors are molded from respectively different metal alloys having correspondingly different properties.  
     
     
         8 . The method of  claim 7  wherein at least one of the fine grain precursors has comparatively more corrosion resistant than another fine grain precursor.  
     
     
         9 . The method of  claim 7  wherein at least one of the fine grain precursors has comparatively higher elongation than another fine grain precursor.  
     
     
         10 . The method of  claim 7  wherein at least one of the fine grain precursors has comparatively higher strength than another fine grain precursor.  
     
     
         11 . The method of  claim 6  wherein reinforcing elements are disposed between the fine grain precursors to form a composite ultra fine grain structured sheet form.  
     
     
         12 . The method of  claim 11  wherein the reinforcing elements are selected from the group consisting of whiskers, graphite fibers, ceramic fibers, wires, wire mesh and metal fibers.  
     
     
         13 . The method of  claim 1  wherein rapidly solidifying the metal alloy material is at a cooling rate of at least 80 C/sec to form the fine grain precursor.  
     
     
         14 . The method of  claim 1  wherein the fine grain precursor has a thickness not exceeding about 4 mm.  
     
     
         15 . The method of  claim 1  wherein the fine grain precursor has a total porosity not exceeding about 2 percent.  
     
     
         16 . The method of  claim 1  wherein the fine grain precursor has a gas porosity not exceeding about 1 percent.  
     
     
         17 . The method of  claim 1  wherein the deformation strain is at a strain rate and the step of imparting plastic deformation is performed while the fine grain precursor is heated to a temperature, wherein the strain rate, the temperature and the deformation strain cooperate to recrystallize the fine grain precursor to the ultra fine grain structured sheet form.  
     
     
         18 . The method of  claim 17  wherein the fine grain precursor is recrystallized by a mechanism including continuous dynamic recrystallization producing the ultra fine grain structured sheet form with at least 50 percent high angle boundaries.  
     
     
         19 . The method of  claim 17  wherein the ultra fine grain structured sheet form has an intensity of basal [0002] texture not exceeding about 5.  
     
     
         20 . The method of  claim 17  wherein the ultra fine grain structured sheet form has a yield strength anisotropy not exceeding about 10 percent.  
     
     
         21 . The method of  claim 17  wherein the strain rate is in the range of approximately 0.1 to 50 s −1 .  
     
     
         22 . The method of  claim 17  wherein the temperature is in the range of approximately 150 C to 450 C.  
     
     
         23 . The method of  claim 17  wherein the strain rate ({acute over (ε)}) and the temperature (T) produce a Zener factor (Z) of greater than about 10 9  s −1  as determined by the formula Z={{acute over (ε)}×exp(Q/RT)} −0.2 , where Q is the activation energy (135 kj mol −1 ), and R is the gas constant.  
     
     
         24 . The method of  claim 17  wherein the deformation strain is at least 0.5.  
     
     
         25 . The method of  claim 17  wherein imparting plastic deformation occurs substantially by slip between grain boundaries of the fine grain precursor with less than about 10 percent twinning of the grain structure.  
     
     
         26 . The method of  claim 17  wherein imparting plastic deformation occurs without substantial shear banding of the grain structure.  
     
     
         27 . The method of  claim 1  wherein the step of molding and solidifying develops a multiphased microstructure in the fine grain precursor.  
     
     
         28 . The method of  claim 27  wherein the multiphased microstructure includes pinning particles that minimize grain growth.  
     
     
         29 . The method of  claim 1  wherein the step of imparting plastic deformation includes the step of causing the formation of new grain boundaries having high misorientation suitable for warm forming or superplastic forming.  
     
     
         30 . The method of  claim 1  wherein the molding step and the imparting plastic deformation step are performed in an integrated apparatus.  
     
     
         31 . The method of  claim 1  wherein the molding step and the imparting plastic deformation step are performed by separate machines.  
     
     
         32 . The method of  claim 1  wherein the molding step includes semisolid metal injection molding of the metal alloy material.  
     
     
         33 . The method of  claim 32  wherein a solids content of the semisolid metal material does not exceed about 30 percent.  
     
     
         34 . The method of  claim 32  wherein a solids content of the semisolid metal material does not exceed about 10 percent.  
     
     
         35 . The method of  claim 32  wherein the semisolid metal injection molding includes delivering the semisolid metal material to a mold via a hot runner system.  
     
     
         36 . The method of  claim 35  wherein a plurality of the fine grain precursors are formed with at least 80 percent production yield.  
     
     
         37 . The method of  claim 32  wherein the semisolid metal material is injected with a screw shot velocity of at least 1.5 m/sec.  
     
     
         38 . The method of  claim 32  wherein the molding step further includes providing argon gas to the metal alloy material.  
     
     
         39 . The method of  claim 1  wherein the molding step further includes extruding of the metal alloy material.  
     
     
         40 . The method of  claim 1  wherein the molding step further includes vacuum molding of the metal alloy material.  
     
     
         41 . The method of  claim 1  further comprising, after the step of imparting plastic deformation, the step of net shaping the ultra fine grain structured sheet to form a part.  
     
     
         42 . The method of  claim 41  further comprising the step of heat treating the net shaped part to impart creep resistance to the net shaped part.  
     
     
         43 . The method of  claim 41  wherein the step of net shaping includes one of stamping, drawing, deep drawing and superplastic forming.  
     
     
         44 . The method of  claim 41  wherein the step of net shaping forms an automotive component.  
     
     
         45 . An apparatus for performing the method of  claim 1 .  
     
     
         46 . An article formed by the method of  claim 1 .  
     
     
         47 . The method of  claim 1  wherein the step of imparting plastic deformation includes die pressing of the fine grain precursor.  
     
     
         48 . The method of  claim 1  wherein the step of imparting plastic deformation includes rolling the fine grain precursor.  
     
     
         49 . The method of  claim 48  wherein the step of imparting plastic deformation further includes constraining edges of the fine grain precursor.  
     
     
         50 . The method of  claim 49  wherein the edges of the fine grain precursor are constrained by a Turks Head arrangement.  
     
     
         51 . The method of  claim 1  wherein the step of imparting plastic deformation includes rolling the fine grain precursor in a plurality of rolling passes with a plurality of respective deformation strains.  
     
     
         52 . The method of  claim 51  wherein the corresponding deformation strain of each rolling pass is at least 50 percent.  
     
     
         53 . The method of  claim 52  wherein the step of rolling includes a first rolling pass at a temperature above ambient, wherein each successive pass is at a lower temperature.  
     
     
         54 . The method of  claim 52  wherein the plurality of rolling passes are cross rolled.  
     
     
         55 . The method of  claim 1  wherein the step of imparting plastic deformation includes extrusion of the fine grain precursor.  
     
     
         56 . The method of  claim 1  wherein the step of imparting plastic deformation includes forging of the fine grain precursor.  
     
     
         57 . The method of  claim 1  wherein the step of imparting plastic deformation includes flow forming of the fine grain precursor.  
     
     
         58 . The method of  claim 1  wherein the sheet form is provided having a grain structure of less than about 5 micrometers.  
     
     
         59 . The method of  claim 1  wherein the sheet form is provided having a grain structure of less than about 2 micrometers.  
     
     
         60 . The method of  claim 1  wherein the sheet form is provided having a grain structure of less than about 1 micrometer.  
     
     
         61 . The method of  claim 1  wherein the precursor is provided having a grain structure of less than about 10 micrometer.  
     
     
         62 . The method of  claim 1  wherein the precursor is provided having a grain structure of less than about 5 micrometer.  
     
     
         63 . The method of  claim 1  wherein the step of imparting plastic deformation is performed while the precursor is heated above ambient.  
     
     
         64 . The method of  claim 1  wherein the magnesium metal alloy is provided with a moisture content less than about 0.1 percent.  
     
     
         65 . The method of  claim 1  wherein the step of imparting plastic deformation includes: 
 plastically deforming the fine grain precursor by a combination of alternating tensile strain and compressive strain to form an SWP sheet, wherein the steps of providing a metal material, molding and rapidly solidifying and plastically deforming are repeated to form a plurality of SWP sheets;    stacking the plurality of SWP sheets to form a SWP stack; and    plastically compressing the SWP stack to form the ultra fine grain structured sheet form.    
     
     
         66 . The method of  claim 65  wherein the step of plastically deforming includes corrugating the fine grain precursor in a first direction and subsequently corrugating the fine grain precursor in a second direction.  
     
     
         67 . The method of  claim 66  wherein the step of plastically deforming the fine grain precursor further includes flattening the corrugated fine grain precursor.  
     
     
         68 . The method of  claim 67  wherein the compressive strain is imparted at least in part by flattening the work piece while constraining lengthening of the work piece in at least one direction.  
     
     
         69 . An apparatus for refining grain structure and producing ultra-fine grained metal material sheets, the apparatus comprising: 
 a receptacle having an inlet, a discharge outlet remote from the inlet, and a chamber defined between the inlet and the discharge outlet;    a feeder coupled with the inlet, the feeder configured to introduce a metal material into the chamber via the inlet;    a heating device for transferring heat to the metal material located within the chamber such that the metal material is at a temperature above its solidus temperature;    discharge means for discharging the metal material from the receptacle through the discharge outlet;    forming means for forming and rapidly solidifying the discharged metal material into a fine grained precursor; and    plastic deformation means including a pair of opposing forming members for imparting deformation strain into the precursor article forming a sheet of the metal material having an ultra-fine grain size.    
     
     
         70 . The apparatus of  claim 69  wherein the opposed forming members are dies.  
     
     
         71 . The apparatus of  claim 69  wherein the opposed forming members are rolls.  
     
     
         72 . The apparatus of  claim 69  further including means for stacking a plurality of the precursor articles into a stack, and wherein the pair of opposing forming members are configured for imparting deformation strain into the stack to form the sheet of the metal material having the ultra fine grain size.  
     
     
         73 . The apparatus of  claim 72  wherein the plastic deformation means further including means for imparting tensile and compressive strain into the precursor article, the plastic deformation means deforming the precursor article into a corrugated work piece and including a second pair of opposing forming members having protrusions formed on a surface thereof, the protrusions of one second forming member being offset from the protrusions of the opposing second forming member; the plastic deformation means further including flattening means for flattening the corrugated work piece, wherein the stacking means stacks a plurality of the flattened work pieces to form the stack.  
     
     
         74 . The apparatus of  claim 73  wherein the second opposed forming members are dies.  
     
     
         75 . The apparatus of  claim 73  wherein the second opposed forming members are rolls.  
     
     
         76 . The apparatus of  claim 72  wherein the stacking means further including means for disposing reinforcing elements between the precursor articles.  
     
     
         77 . The apparatus of  claim 72  wherein the stacking means further includes means for arranging the precursor articles in a pre-determined position.  
     
     
         78 . The apparatus of  claim 69  further comprising net shaping means for shaping the sheet form of the metal material into a net-shaped article.  
     
     
         79 . The apparatus of  claim 78  wherein the shaping means is one of a drawing press and a superplastic forming machine.  
     
     
         80 . The apparatus of  claim 69  wherein the receptacle, feeder, heating means, discharge means and forming means are part of an injection molding machine.  
     
     
         81 . The apparatus of  claim 69  wherein the receptacle, feeder, heating means, discharge means and forming means are part of a semi-solid metal injection molding machine.