Forged aluminum alloy having excellent strength and ductility and method for producing the same

Abstract

Provided is a hot-forged 6xxx-series aluminum alloy having excellent corrosion resistance and still having both high strength and good ductility. A forged 6xxx-series aluminum alloy having a specific chemical composition after solution treatment is further subjected to warm working to introduce dislocations into the forged aluminum alloy microstructure. This allows the forged aluminum alloy after artificial aging to have a microstructure which has a high dislocation density, includes a large proportion of small angle grain boundaries, and has a high average number density of precipitates. Thus, the resulting forged aluminum alloy has a 0.2% yield strength of 400 MPa or more and an elongation of 10% or more and combines properties necessary for suspension parts.

Description

FIELD OF INVENTION[0001]The present invention relates to a forged aluminum alloy having excellent strength and ductility, and a method for producing the same. Hereinafter, “aluminum” is also simply referred to as “AI”.[0002]As used herein, the term “forged material” refers to a forged aluminum alloy produced (plastically worked) by hot forging.[0003]In the present the present invention, the term “forged material” is used not as a term describing a production process of a product, but as a term which is well-known to be generally used as a technical term and / or a patent term for specifying the state of the product.[0004]Aluminum alloy materials, when having different plastic working histories as in hot-forged materials, extruded materials (extrusions), and rolled materials, quite differ from each other in microstructures and properties, even when having identical alloy chemical compositions. Thus, specifying or defining of the alloy chemical compositions, microstructure, and properti...

AI Technical Summary

Benefits of technology

[0061]To offer or ensure these advantageous effects, the present invention specifies the average dislocation density, the average proportion of small angle grain boundaries, and the average number density of precipitates, as described above, on the microstructure at the central part of the thickness in a thickest portion of the forged material after artificial aging.

[0062]The conditions on the microstructure will be described sequentially below.

[0064]The present invention specifies and controls the dislocation density in an observation plane at the center of the thickness in a thickest portion of the forged material to be in the range of 1.0×1014 to 5.0×1016 per square meter on average, as measured by X-ray diffractometry. This control is performed for higher strength and better ductility of the forged material, in combination with other microstructure controls such as controls on the average proportion of small angle grain boundaries, among grain boundaries, and the average number density of precipitates.

[0065]According to the present invention, the forged material after solution treatment and quenching is subjected to warm working to impart working strain (distortion) to the forged material to thereby introduce dislocations again to the forged material. This controls the forged material to have a dislocation density within the specified range. The configuration thus restrains heterogeneous deformation up to a high strain region or up to rupture, where the deformation is caused by the application of external force upon use typically as an automobile suspension part, and allows the forged aluminum alloy to develop excellent work hardening properties (lower yield ratio and higher elongation). This allows the forged aluminum alloy to have high strength in terms of 0.2% yield strength of 400 MPa or more and good ductility in terms of an elongation of 10% or more. This specification (condition) works in combination with other microstructure conditions or controls, such as conditions on the average proportion of small angle grain boundaries in grain boundaries and the average number density of precipitates.

[0066]The forged aluminum alloy, if having an excessively low dislocation density less than 1.0×1014 per square meter, may have inferior work hardening properties as equivalent to conventional forged materials to which no strain is imparted by the warm working. This may cause early rupture in the high strain region upon the application of external force, when the forged aluminum alloy is used typically as an automobile suspension part.

[0067]In contrast, the forged aluminum alloy, if having an excessively high dislocation density greater than 5.0×1016 per square meter, may include smaller amounts of dislocations introduced and accumulated in a high strain region upon the application of external force, when the forged aluminum alloy is used typically as an automobile suspension part. This may also cause early rupture in the high strain region.

Problems solved by technology

However, even the improvements in chemical compositions and microstructures of hot-forged 6xxx-series aluminum alloys, as disclosed typically in Japanese Patent No. 5110938 and Japanese Patent No. 5723192, are susceptible to improvement so as to give forged aluminum alloys having strength and ductility both at excellent levels, where the strength and ductility properties are mutually contradictory and resist being compatible with each other.