Abstract:
A cast aluminum alloy contains at least five of the following alloy components: 2.5 to 3.3 wt.-% of Si; 0.2 to 0.7 wt.-% of Mg; &lt;0.18 wt.-% of Fe; &lt;0.5 wt.-% of Mn; &lt;0.1 wt.-% of Ti; &lt;0.03 wt.-% of Sr; 0.3 to 1.3 wt.-% of Cr; and &lt;0.1 wt.-% of others, supplemented by Al to add up to 100 wt.-%. The parts cast from the alloy are preferably homogenized by annealing for 1 to 10 hours at 490° C. to 540° C. and tempered for 1 to 10 hours at 150° C. to 200° C. Preferably, the alloy is used for chassis parts in motor vehicles.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicants claim priority on and this application is a continuation under 35 U.S.C. 120 of International Application No. PCT/DE2008/001818 filed Nov. 5, 2008, which claims priority under 35 U.S.C. 119 of German Application No. 10 2007 053 159.3 filed Nov. 8, 2007 and German Application No. 10 2008 050 886.1 filed Oct. 9, 2008. The International Application under PCT Article 21(2) was not published in English. Applicants also claim priority under 35 U.S.C. 119 of German Application No. 10 2007 053 159.3 filed Nov. 8, 2007 and German Application No. 10 2008 050 886.1 filed Oct. 9, 2008. The disclosure of the aforesaid International Application and German applications are incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to aluminum (Al) casting alloys, particularly for chassis applications. 
         [0004]    2. Description of the Related Art 
         [0005]    For this purpose, sub-eutectic Al alloys having an Si content between 7 and 12 wt.-% are generally used. In gravity chill-casting, the alloy AlSi11Mg is frequently used; in low-pressure chill-casting the alloy AlSi7Mg is frequently used. 
         [0006]    Low-Si AlSiMg alloys, which are characterized by clearly improved mechanical properties as compared with the conventional AlSi casting alloys mentioned above, are known from WO 2007/025528 A2. 
       SUMMARY OF THE INVENTION 
       [0007]    Proceeding from this state of the art, it is an object of the invention to improve low-Si Al alloys with regard to their mechanical properties. 
         [0008]    These and other objects are achieved, according to the invention, by means of an Al casting alloy that contains at least five of the alloy components listed below
   Si: 2.5 to 3.3, preferably 2.7 to 3.1 wt.-%   Mg: 0.2 to 0.7, preferably 0.3 to 0.6 wt.-%   Fe: &lt;0.18, preferably 0.05 to 0.16 wt.-%   Mn: &lt;0.5, preferably 0.05 to 0.4 wt.-%   Ti: &lt;0.1, preferably 0.01 to 0.08 wt.-%   Sr: &lt;0.03, preferably 0.01 to 0.03 wt.-%   Other: &lt;0.1 wt.-%
 
and, in addition, Cr in an amount that increases the strength of the alloy, as another alloy component, supplemented to 100 wt.-% with Al, in each instance.
   
 
         [0016]    In another aspect, these and other objects are achieved according to the invention, by means of an Al casting alloy that contains at least five of the alloy components listed below
   Si: 2.5 to 3.3, preferably 2.7 to 3.1 wt.-%   Mg: 0.2 to 0.7, preferably 0.3 to 0.6 wt.-%   Fe: &lt;0.18, preferably 0.05 to 0.16 wt.-%   Mn: &lt;0.5, preferably 0.05 to 0.4 wt.-%   Ti: &lt;0.1, preferably 0.01 to 0.08 wt.-%   Sr: &lt;0.03, preferably 0.01 to 0.03 wt.-%   Cr: 0.3 to 1.3, preferably 0.4 to 1.0, particularly preferably 0.5 to 0.8 wt.-%   Other: &lt;0.1 wt.-%
 
and is supplemented to 100 wt.-% with Al, in each instance.
   
 
         [0025]    Such an Al casting alloy is stronger, more impact-resistant, and more ductile as compared with the state of the art. 
         [0026]    The preferred alloying-in of Cr in the amounts stated leads to a further significant improvement in the mechanical properties, which can already be recorded in the casting state, but particularly after solution annealing and aging, if applicable. 
         [0027]    In particular, it has been shown that undesirable iron precipitates can be transformed into a more advantageous morphology, already in the casting state, by means of such additions of chrome. 
         [0028]    For chassis applications, particularly for wheel-guiding components, overall increased mechanical characteristic values can be obtained in this manner. 
         [0029]    The alloys according to the invention can contain contaminants that result from production, for example Pb, Ni, Zn, etc., as they are generally known to a person skilled in the art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0030]    In an advantageous embodiment, CuNi is contained as an additional alloy component, by being alloyed in at the same time. It has been shown that additions of copper or nickel alone do not lead to any significant improvement in the mechanical properties. Alloying in copper and nickel at the same time, however, opens up new possibilities for use of the alloy, particularly in the area outside of the chassis, for components subject to temperature stress, preferably for applications close to the engine. 
         [0031]    The alloys according to the invention demonstrate an improved strength/expansion ratio as compared with known Al casting alloys. 
         [0032]    Fundamentally, a permanent-mold casting method is suitable as a production method for work pieces, components, or parts for or of chassis parts of motor vehicles, in particular, from the casting alloy according to the invention. Because of the very good mechanical properties in the case of work pieces, components, or parts that are subject to great stress, gravity chill-casting and low-pressure chill-casting are particularly suitable as production methods. Particularly in the case of pressure-supported casting methods, for example the low-pressure counter-pressure casting process (CPC process), semi-solid casting process, as well as other pressure-supported casting methods, such as squeeze-casting, casting/forging such as hybrid processes consisting of forging a cast preform available under the trademark COBAPRESS, or molding system automated low-pressure sand-casting, better mechanical technological properties result from the good casting structure. In this connection, the counter-pressure chill-casting process (CPC process) is particularly preferred. 
         [0033]    It can furthermore be advantageous if the alloy has a fine grain. For this purpose, so-called grain refiners are added to the alloy. Grain refinement is a melt treatment. The term “grain refinement” is understood to mean an artificial increase in the number of seed crystals in the melt, which is brought about by the introduction and distribution of outside seed crystals. In this way, better feed capacity by means of improved mass feed, in particular, improved mold-filling and flow capacity, a reduction in the tendency to develop porosity and heat cracks, and a resulting increase in ductility, as well as a better surface composition of the casting alloy are achieved. 
         [0034]    In order to achieve the advantages mentioned above or to develop them even further, it is advantageous if the cast components are heat-treated, particularly with the following parameters: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Solution annealing 
                 490 to 540° C. for 1 to 10 hours 
               
               
                   
                 Annealing 
                 150 to 200° C. for 1 to 10 hours 
               
               
                   
                   
               
             
          
         
       
     
         [0035]    For some application cases, however, it can also be advantageous to undertake only a one-step annealing treatment, generally known as T4, T5, or 0, for example. 
         [0036]    An increase in strength of the castings can advantageously be achieved by means of quenching the castings in water, while they are still hot, instead of allowing them to cool off slowly in air. 
         [0037]    Aside from the advantages that have already been mentioned, which components composed of alloys according the invention demonstrate, the corrosion resistance is also significantly increased, due to the absence of the alloy components Cu and Zn. The product is also relatively inexpensive, because no alloy additives that would make it more expensive, such as Rare Earth (RE) metals, for example, are used, the usual melt treatment can be applied, and no special effort is required for separation of circuits. Likewise, for cost reasons, preferably no Ag is used as an alloy component. 
         [0038]    Also, an excellent strength/expansion ratio is present, with excellent castability. The castability allows a casting that is free of large defects, known as blowholes, for one thing, and for another, the microstructure is positively influenced, in such a manner that the number of internal notches, which reduce elongation to fracture, is kept as low as possible. 
         [0039]    The mold-filling capacity is also improved in the presence of Cr, according to the invention. 
         [0040]    Illustrative examples of the aluminum casting alloy are set forth below: 
       EXAMPLE 1 
       [0041]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Other: &lt;0.1 wt.-%
 
wherein Cr in an amount that increases alloy strength is contained as another alloy component, supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 2 
       [0049]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.7 to 3.1 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: 0.05 to 0.4 wt.-%;   Ti: 0.01 to 0.08 wt.-%;   Sr: 0.01 to 0.03 wt.-%
 
wherein Cr in an amount that increases alloy strength is contained as another alloy component, supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 3 
       [0056]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.3 to 1.3 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 4 
       [0065]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.4 to 1.0 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 5 
       [0074]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 6 
       [0083]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.7 to 3.1 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: 0.05 to 0.4 wt.-%;   Ti: 0.01 to 0.08 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.3 to 1.3;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 7 
       [0092]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.7 to 3.1 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: 0.05 to 0.4 wt.-%;   Ti: 0.01 to 0.08 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.4 to 1.0;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 8 
       [0101]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.7 to 3.1 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: 0.05 to 0.4 wt.-%;   Ti: 0.01 to 0.08 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.5 to 0.8;   Other: &lt;0.1 wt.-%   
 
       EXAMPLE 9 
       [0110]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 10 
       [0119]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: 0.05 to 0.4 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 11 
       [0128]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: 0.01 to 0.08 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 12 
       [0137]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 13 
       [0146]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 14 
       [0155]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: &lt;0.18 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: &lt;0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 15 
       [0164]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.5 to 0.8 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 16 
       [0173]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.2 to 0.7 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.4 to 1.0 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 17 
       [0182]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.5 to 3.3 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.4 to 1.0 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
       EXAMPLE 18 
       [0191]    An aluminum casting alloy that contains alloy components listed below
   Si: 2.7 to 3.1 wt.-%;   Mg: 0.3 to 0.6 wt.-%;   Fe: 0.05 to 0.16 wt.-%;   Mn: &lt;0.5 wt.-%;   Ti: &lt;0.1 wt.-%;   Sr: 0.01 to 0.03 wt.-%;   Cr: 0.4 to 1.0 wt.-%;   Other: &lt;0.1 wt.-%
 
and supplemented to 100 wt.-% with Al.
   
 
         [0200]    The invention furthermore relates to the use of such Al casting alloys for work pieces, components, or parts for or of chassis parts of motor vehicles. The alloy according to the invention has proven to be particularly suitable for components subject to greater stress, such as wheel brackets or pivot bearings. The low-pressure counter-pressure chill-casting process (CPC process) is used as a preferred method for the production of such components that are subject to greater stress. 
       EXAMPLE 
       [0201]    In order to determine the mechanical properties of the alloy AlSi3Mg0.6Cr0.7, a so-called “French tension rod” according to DIN 50125 is cast in the so-called “French chill mold,” using the gravity chill-casting method. Subsequently, heat treatment T6 takes place, whereby the sprue and the feeder are cut off only after the heat treatment, in order to counteract possible distortion of the sample. The mechanical properties of tensile strength R m , yield strength R p 0.2, and ultimate elongation A5 according to DIN10002 are determined. 
         [0202]    After a T6 heat treatment, an increase in the ultimate elongation by 3 percentage points can be determined, which is accompanied by an increase in the tensile strength by approximately 37 MPa. In this connection, the yield strength demonstrates a level that remains the same. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 R m  [MPa] 
                 R p 0.2 [MPa] 
                 A5 [%] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Base 
                 285.5 
                 203.0 
                 8.5 
               
               
                   
                 AlSi3Mg0.6 
               
               
                   
                 Base + Cr 
                 315.2 
                 215.4 
                 10.8 
               
               
                   
                 AlSi3Mg0.6Cr0.7 
               
               
                   
                   
               
             
          
         
       
     
         [0203]    Although several embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.