Aluminum alloy plate having excellent moldability and bake finish hardening properties

Abstract

An aluminum alloy sheet excellent in terms of formability and bake hardenability is provided. The aluminum alloy sheet contains, in terms of mass %, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0% and Sn: 0.005 to 0.3%, with the remainder being Al and unavoidable impurities. A differential scanning calorimetry curve of the aluminum alloy sheet has an endothermic peak in a temperature range of 150 to 230° C. and an exothermic peak in a temperature range of 240 to 255° C. The endothermic peak corresponds to a dissolution of a Mg—Si cluster and has a peak height of 8 μW / mg or less, including 0 μW / mg. The exothermic peak corresponds to a formation of a Mg—Si cluster and has a peak height of 20 μW / mg or larger.

Description

TECHNICAL FIELD[0001]The present invention relates to an Al—Mg—Si alloy sheet. The aluminum alloy sheet referred to in the present invention means an aluminum alloy sheet that is a rolled sheet such as a hot rolled sheet or a cold rolled sheet and has been subjected to refining such as a solution heat treatment and a quenching treatment, but is not yet subjected to a press forming and a bake hardening treatment. Further, aluminum is hereinafter also referred to as Al.BACKGROUND ART[0002]In recent years, because of environmental awareness and the like, the society's requirement for weight reduction in a vehicle such as an automobile has been steadily increasing. In order to respond to such requirement, as a material for a large body panel structure (an outer panel or an inner panel) of an automobile instead of a steel material such as a steel sheet, application of an aluminum alloy material excellent in formability and bake hardenability and lighter in weight has been increasing.[000...

AI Technical Summary

Benefits of technology

The alloy achieves a 0.2% proof stress reduced to 110 MPa or less in forming and increased to 200 MPa or greater after bake hardening, while maintaining a yield ratio of less than 0.50, thereby improving formability and bake hardenability, reducing face strains, and ensuring desired mechanical properties.

Problems solved by technology

Here, the 6000-series aluminum alloy had an advantage of having excellent BH response, but had a problem of having aging properties at room temperature, that is, of age hardening during retention at room temperature after solution heat treatment and quenching treatment to increase the strength, thereby deteriorating formability into a panel, particularly the bendability.

Particularly, in the outer panel subjected to severe bending, there was such a problem that, although forming was possible without any problem immediately after manufacturing, cracking occurred in hem working after the lapse of 1 month.

Moreover, in the case where such room-temperature aging is great, a problem also occurs in that the BH response deteriorate and the proof stress is not improved to the strength required as a panel by heating during an artificial aging (hardening) treatment at a comparatively low temperature, such as a bake treatment and the like of the panel after forming described above.

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