High-strength aluminum alloy extruded shape exhibiting excellent corrosion resistance, ductility, and hardenability, and method for producing the same

Abstract

An Al—Mg—Si-based high-strength aluminum alloy extruded shape exhibits excellent corrosion resistance and ductility, and exhibits excellent hardenability during extrusion (i.e., ensures high productivity). A method for producing the same is also disclosed. The high-strength aluminum alloy extruded shape includes 0.65 to 0.90 mass % of Mg, 0.60 to 0.90 mass % of Si, 0.20 to 0.40 mass % of Cu, 0.20 to 0.40 mass % of Fe, 0.10 to 0.20 mass % of Mn, and 0.005 to 0.1 mass % of Ti, with the balance being Al and unavoidable impurities, the aluminum alloy extruded shape having a stoichiometric Mg2Si content of 1.0 to 1.3 mass %, an excess Si content relative to stoichiometric Mg2Si of 0.10 to 0.30 mass %, and a total content of Fe and Mn of 0.35 mass % or more.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a U.S. National Stage Application of International Application No. PCT / JP2013 / 052002 filed on Jan. 30, 2013, and published in Japanese as WO 2013 / 115227 A1 on Aug. 8, 2013. This application claims priority to Japanese Application No. 2012-018486 filed on Ja. 31, 2012. The disclosures of the above applications are incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to an extruded shape produced using an Al—Mg—Si-based aluminum alloy.BACKGROUND ART[0003]In recent years, a reduction in weight of automobiles aimed to improve driving performance and reduce fuel consumption has been desired from the viewpoint of environment protection.[0004]Use of an aluminum alloy extruded shape as an automotive structural material has been studied in order to meet the requirements for reducing fuel consumption by way of a reduction in weight.[0005]An automotive structural material is required to exhibit high...

AI Technical Summary

Benefits of technology

The invention improves the proof stress of a magnesium silicon alloy while still ensuring its extrudability by setting the stoichiometric Mg2Si content to 1.00 to 1.30% and the excess Si content relative to stoichiometric Mg2Si to 0.10 to 0.30%. By adding a certain amount of iron and manganese, the alloy achieves high strength and high ductility through air-cooling press quenching. The "Fe+Mn≧0.35 mass %" formula is important for achieving this combination of properties.

Problems solved by technology

However, a 7000 series aluminum alloy (natural age hardening alloy) has a drawback in that processing becomes difficult due to hardening when the time elapsed from extrusion to bending is long.

Moreover, a 7000 series aluminum alloy shows a decrease in corrosion resistance under a stress environment.

An extruded shape formed of a known high-strength 6000 series aluminum alloy exhibits high tensile strength, but exhibits insufficient elongation, and easily produces cracks during bending.

However, since a difference is in cooling rate occurs between each cross-sectional area due to the cross-sectional shape of the extruded shape, the difference in thickness, and the like, the extruded shape shows a non-uniform temperature distribution during cooling, and strain occurs.

Therefore, the dimensional accuracy deteriorates, and it is difficult to reduce the thickness of the cross-sectional profile.

The water-cooling press quenching treatment has another disadvantage in that an increase in cost occurs as compared with an air-cooling quenching treatment.

However, since the cooling rate is limited, high strength may not be obtained depending on the alloy composition, and a deterioration in ductility may occur although high strength can be obtained.

However, it is considered that the alloy composition disclosed in JP-A-2002-285272 provides excellent corrosion resistance, but achieves a proof stress of only about 220 MPa (i.e., cannot sufficiently contribute to a reduction in weight of the product).

Since a water-cooling press quenching treatment is normally used in JP-A-2002-285272, it is considered that the extrusion productivity is low.

Since it is necessary to add Cr that achieves sharp quench sensitivity, it is difficult to improve the proof stress using an air-cooling means.

Images