Method of manufacturing an Al—Mg—Mn alloy plate product having an improved corrosion resistance
The invention relates to a method of manufacturing an Al—Mg—Mn aluminium alloy plate product having a final gauge in the range of 3 mm or more, the method comprising the steps of: (a) providing a rolling feedstock material of an aluminium alloy having a composition comprising of Mg 3.5-5.3% and Mn 0.20-1.2%; (b) preheating and/or homogenisation; (c) hot rolling of the rolling feedstock to a rolled final gauge; (d) a first cold working operation selected from the group consisting of (i) stretching in a range of 3% to 20%, and (ii) cold rolling with a cold rolling reduction in a range of 5% to 25%; (c) annealing of the cold worked plate at a temperature in a range of 200° C. to 280° C.; (f) a second cold working operation selected from the group consisting of (i) stretching in a range of 0.4% to 3%, and (ii) cold rolling with a cold rolling reduction in a range of 0.5% to 5%.
1. A method of manufacturing an Al—Mg—Mn aluminium alloy plate product having a final gauge in a range of 3 mm or more, the method comprising the steps of:
(a) providing a rolling feedstock material of an aluminium alloy having a composition comprising of, in wt. %,
Mg 3.5% to 5.3%
Mn 0.20% to 1.2%
Fe up to 0.4%
Si up to 0.4%
Cu up to 0.10%
Cr up to 0.25%
Zr up to 0.25%
Zn up to 0.2%
Ti up to 0.15%,
unavoidable impurities and the balance aluminium;
(b) preheating and/or homogenisation;
(c) hot rolling of the rolling feedstock to a rolled final gauge in a range of 3 mm to 310 mm;
(d) a first cold working operation selected from the group consisting of (i) stretching in a range of 3% to 20%, and (ii) cold rolling with a cold rolling reduction in a range of 5% to 25%, to produce a cold worked plate;
(e) annealing of the cold worked plate at an annealing temperature in a range of 200° C. to 280° C.;
(f) cooling the annealed plate from the annealing temperature to a temperature of about 200° C. at a rate of not more than 10° C. per hour, cooling from the temperature of about 200° C. to a temperature below about 85° C. at a higher cooling rate, and then further cooling the annealed plate to ambient temperature; and
(g) a second cold working operation selected from the group consisting of (i) stretching in a range of 0.4% to 3%, and (ii) cold rolling with a cold rolling reduction in a range of 0.5% to 5%,
wherein the Al—Mg—Mn aluminium alloy plate product has a mass loss less than 25 mg/cm 2 , as tested per ASTM G67-13.
2. The method according to claim 1 , further comprising sensitizing the Al—Mg—Mn aluminium alloy plate product, wherein the Al—Mg—Mn aluminium alloy plate product before and after sensitization is PA or PB, as tested per ASTM G66-99.
3. The method according to claim 1 , further comprising sensitizing the Al—Mg—Mn aluminium alloy plate product, wherein the Al—Mg—Mn aluminium alloy plate product is free of a continuous film of β-phase particles at the grain boundaries after said plate product has been sensitized.
4. The method according to claim 1 , wherein the Al—Mg—Mn aluminium alloy plate product has a final gauge in a range of 3 mm to 120 mm.
5. The method according to claim 1 , wherein during step (e) the annealing is performed in a temperature in the range of 220° C. to 260° C.
6. The method according to claim 1 , wherein the first cold working operation consists of stretching in a range of 3% to 20%.
7. The method according to claim 1 , wherein the second cold working operation consists of stretching in a range of 0.4% to 3%.
8. The method according to claim 1 , wherein the aluminium alloy has a Mn-content of at most 1.05%.
9. The method according to claim 1 , wherein the aluminium alloy has a Mg-content of at least 4.0%.
10. The method according to claim 1 , wherein the aluminium alloy has a Cr-content in a range of 0.04% to 0.25%.
11. The method according to claim 1 , wherein the aluminium alloy has a Zn-content of up to 0.15%.
12. The method according to claim 1 , wherein the Al—Mg—Mn aluminium alloy plate product has an unrecrystallized microstructure.
13. The method according to claim 1 , wherein the Al—Mg—Mn aluminium alloy plate product has a tensile yield strength of at least 200 MPa.
14. The method according to claim 1 , wherein the Al—Mg—Mn aluminium alloy plate product has an ultimate tensile strength of at least 290 MPa.
15. A marine vehicle comprising at least one aluminium plate obtained by the method according to claim 1 .
16. A ship hull comprising an aluminium plate obtained by the method according to claim 1 .
17. The method according to claim 1 , wherein during step (f) the cooling from the annealing temperature to the temperature of about 200° C. is at a cooling rate of not more than 5° C. per hour.