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.

Description

BACKGROUND [0001] 1. Field of the Invention [0002] The present invention relates to producing net shaped components of increased strength. More particularly, the invention relates to producing magnesium alloy sheet components, having micrometer sized grain structures, that can be subsequently used in the production of net shaped sheet components of increased strength. [0003] 2. Related Technology [0004] Over the last several decades, magnesium (Mg) alloy development has been inhibited by certain barriers. While wrought magnesium has the potential for making thinner structures, anisotropy in mechanical properties limits the applications of Mg alloys and their wrought products. The strength of Mg alloys is rather low in certain directions in comparison to most widely used structural materials, such as steels and precipitation-hardened aluminum (Al) alloys. For example, in-plane compression, yield strength can be only 85 MPa in basal textured Mg alloy; AZ31 B Mg alloy sheet in the H24 ...

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Benefits of technology

[0018] In achieving the above object, the inventors have discovered a practical new process and apparatus to generate inexpensive ultra fine grain structured sheet comprising a magnesium metal alloy, where grai

Problems solved by technology

While wrought magnesium has the potential for making thinner structures, anisotropy in mechanical properties limits the applications of Mg alloys and their wrought products.

A high value of normal anisotropy in sheet is helpful for deep drawing, but may not be suitable for other applications, particularly if in-plane strength is also anisotropic.

In fact, this base element has not been a friendly host for extensive alloy strengthening.

The alloying elements that improve corrosion resistance and castability, such as Al, unfortunately introduce eutectic intermetallic phases.

Furthermore, it is difficult to attain efficient age hardening by fine precipitates within the grains, as exemplified by the case of inefficient Al additions.

Elements that promote age hardening, such as rare earth metals, are costly, detrimental to castability and ineffective in resisting corrosion.

At room temperature, “basal a” slip {0001} is predominant, while “prism a” and slip are difficult because of their significantly high critical resolved shear stresses (CRSS), which are reported in regions of high stress concentration such as grain boundaries and twin interfaces.

A single twinning mode cannot fully accommodate plastic deformation.

When basal slip is inhibited at ambient temperatures, twinning deformation can be localized, which leads to low ductility in Mg.

Two major drawbacks restrict the application of wrought Mg alloys.

First the symmetry of hexagonal close packed crystal structures has the effect of limiting the number of independent slip systems, thus providing alloys with poor formability and ductility near room temperature.

), although helpful to overcome the restriction of slip, makes oxidation problems more severe.

However, for HCP metals, such as Mg alloys, grain refinement may also cause texture variation, and inadequate strengthening in certain directions.

These processes are costly, time consuming and have not enjoyed commercial success.

Several other schemes for severe plastic deformation (SPD) have proven to be unpractical for manufacturing larger quantities of ultra-fine grain metals.

When these processes are used in a repeated manner, the overlap of shear zones within the bulk material from individual steps causes extensive grain subdivision and formation of fine grain structure.

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