Aluminum alloy sheet for forming

Abstract

The present invention pertains to an Al—Mg—Si alloy sheet for forming, that contains 0.2-2.0% of Mg, 0.3-2.0% of Si, and 0.005-0.3% of Si (all amounts given with respect to mass), the balance comprising Al and unavoidable impurities, wherein the aluminum alloy sheet for forming is characterized in that the structure of the aluminum alloy sheet is such that the average number density of compounds having a circle-equivalent diameter within a range of 0.3-20 μm as measured by SEM at 500 times magnification is more than 0 / mm2 but not more than 5,000 / mm2, and of the compounds measured by SEM, the average count ratio of compounds that contain 0.5% by mass or more of Sn as identified using an X-ray spectrograph, is 0% or more but less than 50%. This aluminum alloy sheet for forming exhibits high BH response and good formability.

Description

TECHNICAL FIELD[0001]The present invention relates to an Al—Mg—Si alloy sheet for forming. The term “aluminum alloy sheet” used in the present invention means an aluminum alloy sheet that is a rolled sheet, such as a hot-rolled sheet or cold-rolled sheet, and that has undergone refining, such as a solution heat treatment and a quenching treatment, and has not undergone a bake hardening treatment. Hereinafter, aluminum is referred to also as Al.BACKGROUND ART[0002]In recent years, the social request for weight reduction in vehicles including automobiles is increasing more and more due to considerations to the global environment or the like. In order to meet the request, aluminum alloy materials which are excellent in terms of formability and bake hardenability and are more lightweight are coming to be increasingly used as materials for automotive panels, in particular, large body panels such as hood, door and roof (outer panels and inner panels), in place of steel materials such as s...

AI Technical Summary

Benefits of technology

The present invention relates to an Al—Mg—Si alloy sheet for use in the production of panels. The sheet has a microstructure that includes Sn, which at room temperature captures atomic holes to prevent the diffusion of Mg and Si, and at the same time improves the formability of the sheet. During an artificial aging treatment, such as a paint baking treatment, the Sn releases the captured holes and enhances the diffusion of Mg and Si, resulting in an improved strength of the panels. The invention also provides a method for controlling the state of the Sn in the sheet production process to enhance its effectiveness. The resulting sheet has higher formability and improved BH response even after long-term room-temperature aging.

Problems solved by technology

There has hence been a problem in that they, when held at room temperature for several months after a solution quenching treatment, undergo age hardening and increase in strength, thereby deteriorating in formability into panels, in particular, bendability.

Especially in the case of outer panels for which severe bending is performed, even when it can be formed without any problem at one month after the production, there has been a problem in that cracking occurs or the like in hem working at three months after the production.

Moreover, in the case where such room-temperature aging is great, a problem also arises in that the BH response deteriorates and the heating during an artificial aging (hardening) treatment at a relatively low temperature, such as a paint baking treatment of the panel after being formed, does not improve the proof stress to such a degree that the panel comes to have the required strength.