Aluminum alloy sheet with excellent paint-bake hardenability

Patent metadata

Field	Value
Publication number	US-9453273-B2
Application number	US-201314373387-A
Country	US
Kind code	B2
Filing date	Jan 29, 2013
Priority date	Feb 16, 2012
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

This aluminum alloy sheet is a 6000-series aluminum alloy sheet of a specific composition which, after rolling, has undergone solution hardening and reheating as tempering treatments. The aluminum alloy sheet in differential scanning calorimetry gives a curve in which the exothermic-peak heights A, B, and C in respective specific temperature ranges have relationships within specific given ranges to thereby raise the increase in 0.2% proof stress through low-temperature short-time artificial age-hardening to 100 MPa or more.

First claim

The invention claimed is:

1. An aluminum alloy sheet, comprising:
an Al—Mg—Si-based aluminum alloy sheet that comprises, by mass percent, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0%, and Al, and is subjected to solution hardening and reheating as tempering after rolling,
wherein
when an exothermic peak height in a temperature range from 230 to 270° C. is denoted as A, an exothermic peak height in a temperature range from 280 to 320° C. is denoted as B, and an exothermic peak height in a temperature range from 330 to 370° C. is denoted as C on a differential scanning calorimetry curve, the exothermic peak height B is 20 μW/mg or more, a ratio of the exothermic peak height A to the exothermic peak height B A/B is 0.45 or less, and a ratio of the exothermic peak height C to the exothermic peak height B C/B is 0.6 or less, and
when the aluminum alloy sheet is subjected to artificial age hardening of 170° C.×20 min after application of strain of 2%, an increase in 0.2% proof stress in a direction parallel to a rolling direction is 100 MPa or more.

2. The aluminum alloy sheet according to claim 1 , further comprising: one or more of
Mn: from more than 0 to 1.0%,
Cu: from more than 0 to 1.0%,
Fe: from more than 0 to 1.0%,
Cr: from more than 0 to 0.3%,
Zr: from more than 0 to 0.3%,
V: from more than 0 to 0.3%,
Ti: from more than 0 to 0.05%,
Zn: from more than 0 to 1.0%, and
Ag: from more than 0 to 0.2%.

3. The aluminum alloy sheet according to claim 1 , wherein the exothermic peak height B is 50 μW/mg or less.

4. The aluminum alloy sheet according to claim 1 , wherein the ratio of A/B is 0.1 or more.

5. The aluminum alloy sheet according to claim 1 , wherein the ratio of C/B is 0.15 or more.

6. The aluminum alloy sheet according to claim 1 , obtained by a process comprising:
melting and casting an aluminum alloy to obtain an casted aluminum alloy slab,
soaking the casted aluminum alloy slab to homogenize the microstructure of the slab and cooling the slab to room temperature,
hot rolling the slab to obtain a hot-rolled sheet,
optionally annealing the hot-rolled sheet,
cold rolling the hot-rolled sheet to obtain a cold-rolled sheet,
subjecting the cold-rolled sheet to solution and hardening, and
subsequently subjecting the cold-rolled sheet to a reheating treatment comprising
heating the cold-rolled sheet to a first reheating temperature of from 100 to 250° C. at an average heating rate of 10° C./sec or more within one hour and holding the sheet at the first reheating temperature for 5 seconds to 30 minutes,
cooling the sheet from the first reheating temperature to a second reheating temperature of from 70 to 130° C. at an average cooling rate of 1° C./sec or more and holding the sheet at the second reheating temperature for 10 minutes to 2 hours, and
cooling the sheet from the second reheating temperature to room temperature at an average cooling rate of 1° C./hr or more.

Assignees

• Kobe Steel Ltd

Inventors

• Matsumoto Katsushi
• Aruga Yasuhiro
• Shishido Hisao

Classifications

• C22F1/05 Primary

  of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions · CPC title

• C22C21/02

  with silicon as the next major constituent · CPC title

• C22C21/08

  with silicon · CPC title

• C22F1/00

  Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working (apparatus for mechanical working of metal B21, B23, B24) · CPC title