Forged aluminum alloy having excellent strength and ductility and method for producing the same

Abstract

Provided is a hot-forged 6xxx-series aluminum alloy having excellent corrosion resistance and still having both high strength and good ductility. A forged 6xxx-series aluminum alloy having a specific chemical composition after solution treatment is further subjected to warm working to introduce dislocations into the forged aluminum alloy microstructure. This allows the forged aluminum alloy after artificial aging to have a microstructure which has a high dislocation density, includes a large proportion of small angle grain boundaries, and has a high average number density of precipitates. Thus, the resulting forged aluminum alloy has a 0.2% yield strength of 400 MPa or more and an elongation of 10% or more and combines properties necessary for suspension parts.

1 : A forged aluminum alloy having excellent strength and ductility, the forged aluminum alloy comprising, in mass percent:
 Si in a content of 0.7% to 1.5%;   Mg in a content of 0.6% to 1.2%;   Fe in a content of 0.01% to 0.5%;   at least one element selected from the group consisting of:
 Mn in a content of 0.05% to 1.0%; 
 Cr in a content of 0.01% to 0.5%; and 
 Zr in a content of 0.01% to 0.2%; and 
   Al and inevitable impurities,   wherein:   the forged aluminum alloy having a microstructure in an observation plane at a center of a thickness in a thickest portion of the forged aluminum alloy;   the microstructure has a dislocation density of from 1.0×10 14  to 5.0×10 16  per square meter on average as measured by X-ray diffractometry;   the microstructure comprises small angle grain boundaries with a tilt angle of 2° to 15° in an average proportion of 50% or more as measured by SEM-EBSD, the small angle grain boundaries being present around grains having a misorientation of 2° or more; and   the microstructure comprises precipitates in an average number density of 5.0×10 2  per cubic micrometer or more, the precipitates being measurable by a transmission electron microscope (TEM) at 300000-fold magnification.   
     
     
         2 : The forged aluminum alloy according to  claim 1 , further comprising, in mass percent, at least one element selected from the group consisting of:
 Cu in a content of 0.05% to 1.0%;   Ti in a content of 0.01% to 0.1%; and   Zn in a content of 0.005% to 0.25%.   
     
     
         3 : The forged aluminum alloy according to  claim 1 , which has a tensile strength of 420 MPa or more, a 0.2% yield strength of 400 MPa or more, and an elongation of 10% or more. 
     
     
         4 : A method for producing a forged aluminum alloy having excellent strength and ductility, the method comprising:
 preparing an aluminum alloy ingot comprising, in mass percent:
 Si in a content of 0.7% to 1.5%; 
 Mg in a content of 0.6% to 1.2%; 
 Fe in a content of 0.01% to 0.5%; and 
 at least one element selected from the group consisting of:
 Mn in a content of 0.05% to 1.0%; 
 Cr in a content of 0.01% to 0.5%; and 
 Zr in a content of 0.01% to 0.2%, and 
 
 Al and inevitable impurities; 
   subjecting the aluminum alloy ingot sequentially to homogenization and hot-forging to give a forged material; and   subjecting the forged material sequentially to solution treatment, quenching, warm working, and artificial aging in the specified sequence,   wherein:   the forged material after artificial aging has a microstructure in an observation plane at a center of a thickness in a thickest portion of the forged material;   the microstructure has a dislocation density of from 1.0×10 14  to 5.0×10 16  per square meter on average as measured by X-ray diffractometry;   the microstructure comprises small angle grain boundaries with a tilt angle of 2° to 15° in an average proportion of 50% or more as measured by SEM-EBSD, the small angle grain boundaries being present around grains having a misorientation of 20 or more; and   the microstructure comprises precipitates in an average number density of 5.0×10 2  per cubic micrometer or more, the precipitates being measurable by a TEM at 300000-fold magnification.