ULTRA HIGH STRENGTH 6XXX FORGED ALUMINIUM ALLOYS

Abstract

An aluminium alloy forged product obtained by casting a billet from a 6xxx aluminium alloy comprising: Si: 0.7-1.3 wt. %; Fe: <0.5 wt. %; Cu: 0.1-1.5 wt. %; Mn: 0.4-1.0 wt. %; Mg: 0.6-1.2 wt. %; Cr: 0.05-0.25 wt. %; Zr: 0.05-0.2 wt. %; Zn: <0.2 wt. %; Ti: <0.2 wt. %, the rest being aluminium and inevitable impurities. The product optionally has an ultimate tensile strength higher than 400 MPa.

Claims

1. An aluminium alloy forged product wherein the process to obtain the product comprises: a) casting a billet from a 6xxx aluminium alloy comprising: Si: 0.7-1.3 wt. %; Fe: <0.5 wt. %; Cu: 0.1-1.5 wt. %; Mn: 0.4-1.0 wt. %; Mg: 0.6-1.2 wt. %; Cr: 0.05-0.25 wt. %; Zr: 0.05-0.2 wt. %; Zn: <0.2 wt. %; Ti: <0.2 wt. %, the rest being aluminium and inevitable impurities; b) homogenising the cast billet at a temperature TH which is 5° C. to 80° C. lower than solidus temperature Ts, optionally TH in the range of 500-560° C., for a duration between 2 and 10 hours to ensure high level of dissolution of constituent particles while ensuring precipitation and controlled coarsening of dispersoid phases; c) quenching said billet down to room temperature by using water quench system; d) heating the homogenised billet to a temperature Th between (Ts−5° C.) and (Ts−125° C.); e) extruding said billet through a die to produce a solid section with an exit temperature (optionally 530° C.) lower than Ts (optionally 550° C.), and with an extruding ratio of at least 8; f) quenching the extruded product down to room temperature by using water quench system; g) stretching the extruded product to obtain a plastic deformation optionally between 0.5% and 10%, optionally up to 5%; h) heating cut-to-length extruded rod to forging temperature, optionally between 400 and 520° C.; i) forging in heated mould between 150 and 350° C.; j) separate solutionising at a temperature between 530 and 560° C. for a duration between 2 min. and 1 hour; k) water quenching the forged and solutionised material down to room temperature; l) room temperature ageing for a duration between 6 hours and 30 days; m) aging to T6 temper by a one- or multiple-step heat treatment at one or more temperatures ranging from 150 to 200° C. for one or more holding times ranging from 2 to 20 hours. and its ultimate tensile strength is higher than 400 MPa.

2) An aluminium alloy forged product according to claim 1 wherein said 6xxx aluminium alloy comprises Cu: 0.4-1.2 wt. %, optionally 0.6-1.0 wt. %.

3) An aluminium alloy forged product according to claim 1 wherein said 6xxx aluminium alloy comprises Si: 0.9-1.3 wt. %, optionally 1.1-1.3 wt. %.

4) An aluminium alloy forged product according to claim 1 wherein said 6xxx aluminium alloy comprises Mg: 0.7-1.1 wt. %, optionally 0.8-1.0 wt. %.

5) An aluminium alloy forged product according to claim 1 wherein said 6xxx aluminium alloy comprises Mn: 0.5-0.9 wt. %, optionally 0.5-0.7 wt. %.

6) An aluminium alloy forged product according to claim 1 wherein Fe<0.3 wt. %, optionally <0.2 wt. %.

7) An aluminium alloy forged product according to claim 1 wherein its ultimate tensile strength is higher than 450 MPa, and optionally higher than 480 MPa.

8) An aluminium alloy forged product according to claim 1 wherein said product comprises an automotive body-structure part.

9) An aluminium alloy forged product according to claim 1 wherein said product comprises an automotive chassis-suspension part.

10) An aluminium alloy forged product according to claim 1 wherein said product comprises an automotive suspension arm.

11) A process for manufacturing an aluminium alloy forged product according to claim 1 comprising: a) casting a billet from a 6xxx aluminium alloy comprising: Si: 0.7-1.3 wt. %; Fe: <0.5 wt. %; Cu: 0.1-1.5 wt. %; Mn: 0.4-1.0 wt. %; Mg: 0.6-1.2 wt. %; Cr: 0.05-0.25 wt. %; Zr: 0.05-0.2 wt. %; Zn: <0.2 wt. %; Ti: <0.2 wt. %, the rest being aluminium and inevitable impurities; b) homogenising the cast billet at a temperature TH which is 5° C. to 80° C. lower than solidus temperature Ts, optionally TH in the range of 500-560° C., for a duration between 2 and 10 hours to ensure high level of dissolution of constituent particles while ensuring precipitation and controlled coarsening of dispersoid phases; c) quenching said billet down to room temperature by using water quench system; d) heating the homogenised billet to a temperature Th between (Ts−5° C.) and (Ts−125° C.); e) extruding said billet through a die to produce a solid section with an exit temperature lower than Ts (optionally 530° C.) lower than Ts (optionally 550° C.), and with an extruding ratio of at least 8; f) quenching the extruded product down to room temperature by using water quench system; g) stretching the extruded product to obtain a plastic deformation optionally between 0.5% and 10%, optionally up to 5%; h) heating cut-to-length extruded rod to forging temperature, optionally between 400 and 520° C.; i) forging in heated mould between 150 and 350° C.; j) separate solutionising at a temperature between 530 and 560° C. for a duration between 2 min. and 1 hour; k) water quenching the forged and solutionised material down to room temperature; l) room temperature ageing for a duration between 6 hours and 30 days; m) aging to T6 temper by a one- or multiple-step heat treatment at one or more temperatures ranging from 150 to 200° C. for one or more holding times ranging from 2 to 20 hours.

Description

EXAMPLE

[0031] Forged suspension arms were made from two 6xxx aluminium alloys, the first one being of the AA6082 type, the other one according to the invention, starting from extruded round bars with a diameter of 40 mm.

Said bars were extruded by following two different process routes: the current prior art route for AA6082 alloys and the route according to the invention for others.
The chemical compositions of these alloys are shown on Table I in weight %.

TABLE-US-00001 TABLE I Si Fe Cu Mn Mg Cr Ni Zn Ti Pb V Zr AA6082 1.112 0.197 0.061 0.744 0.807 0.193 0.003 0.012 0.029 0.001 Invention 1.3 0.16 0.74 0.53 0.89 0.1 0.04 0.008 0.019 0.0011 0.011 0.13
Homogenised cast billets having a diameter of 308 mm and a length of 1200 mm were heated, introduced into an extrusion press and pressed to form 40 mm in diameter bars.
Forged suspension arms were obtained by following a conventional route for AA6082 alloys:
a) homogenising the cast billet at a temperature T.sub.H close to 480° C., for a duration of 5 hours;
b) cooling said billet down to room temperature;
c) heating the homogenised billet to a temperature T.sub.h close to 500° C.;
c) extruding said billet through a die to produce round bars with an exit temperature close to 530° C.;
d) cooling the extruded product down to room temperature;
e) stretching the extruded product to obtain a plastic deformation close to 1%;
f) heating cut-to-length extruded rod to forging temperature, close to 500° C.;
g) forging in mould heated close to 300° C.;
h) separate solutionising at a temperature close to 530° C. for 30 min.;
i) water quenching the forged material with an intense cooling device down to room temperature;
j) room temperature ageing for a duration of 1 day;
k) ageing to T6 temper by a one-step heat treatment at 175° C. for 8 hours.
Forged suspension arms were obtained by following the route according to the invention for other ones (“Invention”):
a) homogenising the cast billet at a temperature T.sub.H close to 520° C., for a duration of 5 hours;
b) quenching said billet down to room temperature by using water quench system;
c) heating the homogenised billet to a temperature T.sub.h close to 500° C.;
d) extruding said billet through a die to produce round bars with an exit temperature close to 530° C.;
e) quenching the extruded product down to room temperature by using water quench system;
f) stretching the extruded product to obtain a plastic deformation close to 1%;
g) heating cut-to-length extruded rod to forging temperature close to 500° C.;
h) forging in heated mould close to 300° C.;
i) separate solutionising at a temperature close to 550° C. for 30 min.;
j) quenching the forged material with an intense cooling device down to room temperature;
k) room temperature ageing for a duration of 1 day;
l) ageing to T6 temper by a one-step heat treatment at 170° C. for 8 hours.

[0032] Tensile test specimens were machined in the suspension arms. Table 2 shows the ultimate tensile strength (UTS), the yield strength (YS) and the elongation of forged products.

TABLE-US-00002 TABLE 2 Rm Rp0, 2 A Alloy Solutionising Ageing Temper [MPa] [MPa] [%] AA 6082 530° C./ 175° C./ T6 378 358 11 30 min. 8 h AA 6082 530° C./ 175° C./ T6 376 354 12.5 30 min. 8 h Invention 550° C./ 170° C./ T6 481 452 13 30 min. 8 h Invention 550° C./ 170° C./ T6 484 456 12 30 min. 8 h

[0033] The results of table 2 show that the process route according to the invention enables the manufacture of aluminium alloy forged products having significantly higher strength (UTS and YS) than products obtained by a conventional route, and similar elongation.

[0034] Corrosion tests were performed using the ISO 11846B test for 24 hours of exposure time on suspension arms as above, the ones obtained from AA6082 alloy following the prior art route, the other ones according to the invention.

[0035] FIG. 1 shows no significant difference for products according to the invention, with a maximum surface attack depth of 310 microns and a maximum end grain attack depth of 380 microns for the product according to the invention compared to respectively 390 and 320 microns for AA6082 alloys processed through a prior art route.

[0036] These results show that the process route according to the invention enables the manufacture of aluminium alloy extruded products having simultaneously better strength (UTS and YS) and equivalent corrosion resistance than products obtained by a conventional route.