Methods for determining a recovery state of a metal alloy

• US 9,002,499 B2
• Filed: 03/20/2012
• Issued: 04/07/2015
• Est. Priority Date: 03/20/2012
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations LLC (General Motors Company)
• Inventors: Raghavan, Rajesh, Tiwari, Shashank, Mishra, Sushil Kumar
• Primary Examiner(s): Fennema, Robert
• Assistant Examiner(s): WHITTINGTON, ANTHONY T
• Application Number:
  US13/425,356
• Publication Number:
  US 20130253691A1
• Time in Patent Office: 1,113 Days
• Field of Search: 700/145, 148/554, 420/471
• US Class Current: 700/145
• CPC Class Codes: G01N 2223/606 texture
• CPC Class Codes: G01N 2223/615 composite materials, multilayer laminates
• CPC Class Codes: G01N 23/203 Measuring back scattering

Abstract

Methods for determining a recovery state of a metal alloy are disclosed herein. In one example, a fluctuation in a crystallographic grain orientation of the metal alloy is determined by utilizing electron backscatter diffraction (EBSD) data of the metal alloy. A processor of an electron backscatter diffraction machine utilizes a local orientation deviation quantifier to correlate the fluctuation in the crystallographic grain orientation of the metal alloy with a plastic strain recovery of the metal alloy. Other examples of the method are also disclosed herein.

Claims

1. A method for determining a recovery state of a metal alloy, the method comprising:

determining a fluctuation in a crystallographic grain orientation of the metal alloy, the determining being accomplished utilizing electron backscatter diffraction (EBSD) data of the metal alloy; and

by a processor of an electron backscatter diffraction machine, utilizing a local orientation deviation quantifier to correlate the fluctuation in the crystallographic grain orientation of the metal alloy with a plastic strain recovery of the metal alloy, wherein the utilizing includes;

evaluating, by the processor, a local average orientation deviation at each of a plurality of EBSD scan points of the metal alloy from a reference orientation at each of the plurality of EBSD scan points;

plotting, by the processor, an area fraction of the local average orientation deviation at each of the plurality of EBSD scan points of the metal alloy, the EBSD scan points including a scan point for when the metal alloy is in a deformed state and an other scan point for when the metal alloy is in an at least partially recovered state;

identifying, by the processor, θ

_reference, a local orientation deviation angle for the metal alloy in the deformed state, and θ

_recovery, a local orientation deviation angle for the metal alloy in the at least partially recovered state; and

determining that at least partial recovery of the metal alloy has occurred when the θ

_recovery is less than the θ

_reference.

2. The method as defined in claim 1 wherein the metal alloy is a precipitation-hardenable metal alloy.

3. The method as defined in claim 2 wherein the metal alloy is chosen from a precipitation-hardenable aluminum alloy, a precipitation-hardenable copper alloy, and a precipitation-hardenable magnesium alloy.

4. The method as defined in claim 1, further comprising quantifying, by the processor, the recovery state of the metal alloy by generating a scale of the recovery utilizing the θ

_recovery and the θ

_reference.

5. The method as defined in claim 1 wherein the plotting of the area fraction of the local average orientation deviation produces a curve including:

a single peak for θ

_{recrystallization}, a local orientation deviation angle signifying a recrystallization of the metal alloy;

an other single peak for the θ

_recovery, wherein θ

_recovery is greater than θ

_{recrystallization}; and

two peaks, wherein one of the two peaks represents a local orientation deviation angle for partial recovery of the metal alloy, and an other of the two peaks represents a local orientation deviation angle for partial recrystallization.

6. The method as defined in claim 5, further comprising:

quantifying, by the processor, the recovery state of the metal alloy by generating a scale of the recovery utilizing θ

_reference as 0% recovery and θ

_recovery as 100% recovery.

7. The method as defined in claim 1 wherein the evaluating of the local average orientation deviation is accomplished by calculating, by the processor, a difference between a measured orientation and the reference orientation, the reference orientation being a mean kernel orientation, a mean grain orientation, or a grain orientation at a user-specified point inside a grain.

8. The method as defined in claim 1, further comprising generating kinetics data of the plastic strain recovery of the metal alloy utilizing peak orientation deviation data.

9. The method as defined in claim 1 wherein the metal alloy is an automotive part formed by an automotive part forming process.

16. A method of controlling a metal forming process, comprising:

determining a recovery state of a metal alloy by the method of claim 1; and

based on the recovery state of the metal alloy, determining operating parameters of a thermo-mechanical treatment step of the metal forming process.

10. A method for determining a recovery state of a plastically-strained metal alloy, the method comprising:

obtaining electron backscatter diffraction (EBSD) data of the metal alloy;

from the EBSD data, identifying a fluctuation in grain orientations of the metal alloy;

identifying, by a processor of an electron backscatter diffraction machine that generates the EBSD data, a local orientation deviation angle at each of a plurality of scan points in the EBSD by comparing the fluctuation in grain orientations with a reference orientation at each of the plurality of scan points in the EBSD data;

plotting, by the processor, an area fraction for the local orientation deviation angles of each of the plurality of EBSD scan points; and

from the plot, determining that at least partial plastic strain recovery of the metal alloy has occurred.

11. The method as defined in claim 10 wherein the metal alloy is a precipitation-hardenable metal alloy.

12. The method as defined in claim 10 wherein the identifying of the local orientation deviation angles is accomplished by calculating, by the processor, a difference between a measured orientation and the reference orientation, the reference orientation being a mean kernel orientation, a mean grain orientation, or a grain orientation at a user-specified point inside a grain.

13. The method as defined in claim 10 wherein the determining includes:

correlating, by the processor, the fluctuation in the crystallographic grain orientations of the metal alloy by comparing the fluctuation of the at least partially recovered metal alloy with a fluctuation in crystallographic grain orientations of any of the metal alloy at an unrecovered state or the metal alloy in a fully recovered state.

14. The method as defined in claim 10 wherein the electron backscatter diffraction (EBSD) data of the metal alloy is obtained at predetermined times after the metal alloy is subjected to a thermo-mechanical treatment step.

15. The method as defined in claim 14 wherein the thermo-mechanical treatment step involves an annealing step.