HIGH STRENGTH, HIGH STRESS CORROSION CRACKING RESISTANT AND CASTABLE Al-Zn-Mg-Cu-Zr ALLOY FOR SHAPE CAST PRODUCTS

Abstract

The present invention provides an Al—Zn—Mg—Cu casting alloy that provides high strength for automotive and aerospace applications and optimized stress corrosion cracking resistance in highly corrosive and tensile environments. The inventive alloy composition includes about 3.5 wt. % to about 5.5 wt. % Zn; about 1.0 wt. % to about 3.0 wt. % Mg; about 0.5 wt. % to about 1.2 wt. % Cu; less than about 1.0 wt. % Si; less than about 0.30 wt. % Mn; less than about 0.30 wt. % Fe; and a balance of Al and incidental impurities.

Description

RELATED APPLICATION[0001]This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 60 / 826,131, filed Sep. 19, 2006, the contents of which are incorporated by reference herein in its entirety.FIELD OF THE INVENTION[0002]This invention relates generally to aluminum alloys for aerospace and automotive shaped castings having high tensile strength and high resistance to stress corrosion cracking (SCC).BACKGROUND OF THE INVENTION[0003]Cast aluminum parts are used in structural applications in automobile suspensions to reduce weight. The most commonly used group of alloys, Al7SiMg, has well established strength limits. In order to obtain lighter weight parts, higher strength material is needed with established material properties for design. At present, cast materials made of A356.0, the most commonly used Al7SiMg alloy, can reliably guarantee ultimate tensile strength of 290 MPa (42 ksi), and tensile yield strength of 220 MPa (32 ksi) with elongations of...

AI Technical Summary

Benefits of technology

[0007]Generally speaking, the present invention provides an Al—Zn—Mg—Cu alloy for shaped castings having ultimate tensile strengths greater than that achieved by comparable castings of A356, while maintaining corrosion performance suitable for automotive and aerospace applications, specifically including a good resistance to stress corrosion cracking (SCC) in severely corrosive environments of high tensile stress. Broadly, the inventive alloy is composed of

[0030]The inventive Al—Zn—Mg—Cu alloy and method of producing a shaped casting in addition to providing levels of strength and corrosion performance that were previously not obtainable with prior Al—Zn—Mg—Cu alloys, additionally provides acceptable hot cracking performance and fluidity for casting shaped products.

Problems solved by technology

Forged products are disadvantageously more expensive than cast products.

However these exhibit problems in castability, corrosion performance or fluidity, which are not readily overcome.

While the Al—Zn—Mg—Cu alloy disclosed in U.S. patent application Ser. No. 11 / 111,212 provides good general corrosion resistance, it has been determined that the alloy exhibits a less than optimum stress corrosion cracking (SCC) resistance in environments of high tensile stress and corrosion, which could limit it's application.

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