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.

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.