Patent Publication Number: US-2021189525-A1

Title: Method of manufacturing aluminum alloy and aluminum alloy

Description:
CROSS-REFERENCE(S) TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2019-0172978, filed on Dec. 23, 2019 which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technical Field 
     Exemplary embodiments of the present disclosure relate to a method of manufacturing aluminum alloy and an aluminum alloy produced thereby; and, particularly, to an aluminum alloy for high-power engine components. 
     Description of Related Art 
     High-performance vehicles may greatly appeal to consumers seeking driving pleasure, and the development and production thereof are also effective in demonstrating the technology of automobile manufacturers to ordinary consumers. 
     Such a high-performance vehicle inevitably requires a high-power engine. However, as the power of the engine increases, the physical and thermal loads on the material of the engine increase. 
     An alloy used to cast a conventional cylinder head for high-performance vehicles has the following compositions, shown in Table 1, and the cylinder head is manufactured by heat treatment as illustrated in  FIG. 1 . 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Composition 
                 Cu (wt %) 
                 Si (wt %) 
                 Mg (wt %) 
                 Fe (wt %) 
                 Mn (wt %) 
                 Ti (wt %) 
                 Al 
               
               
                   
               
             
            
               
                 AC4CH 
                 0.2 or less 
                 6.5~7.5 
                 0.35~0.45 
                 0.2 or less 
                 0.03~0.1 
                 0.05~0.2 
                 REM. 
               
               
                   
               
            
           
         
       
     
     The main reinforcing elements of the alloy are Mg and Si. Si is an element that affects the castability and strength of the alloy, and the alloy is improved in strength through the formation of Mg 2 Si precipitation phase after heat treatment by Mg. 
     In other words, the alloy is solutionized to evenly dissolve Si and Mg elements in an Al matrix and aged to form an Mg 2 Si compound, resulting in an increase in strength. 
     Although the aluminum for the cylinder head of the conventional gasoline engine has an endurance limit temperature of about 200° C., the test of the high-power engine shows that the temperature of the cylinder head increases from 250° C. to 300° C. For this reason, the use of existing materials may cause insurmountable damage to the cylinder head. 
     That is, the high-power engine is damaged before 1/10 of expected endurance test time due to exposure to high-temperature environment during testing. Hence, it can be seen that the conventional alloy compositions do not withstand the harsh environment of the high-power engine. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY 
     An embodiment of the present disclosure is directed to an aluminum alloy that can be used in a high-power engine by having excellent high-temperature physical properties and high thermal conductivity in favor of performance and fuel efficiency, and a method of manufacturing the same. 
     Other objects and advantages of the present disclosure can be understood by the following description, and become apparent with reference to the embodiments of the present disclosure. Also, it is obvious to those skilled in the art to which the present disclosure pertains that the objects and advantages of the present disclosure can be realized by the means as claimed and combinations thereof. 
     In accordance with an embodiment of the present disclosure, there is provided a method of manufacturing aluminum alloy, which includes solutionizing a cast product made of an aluminum alloy containing 0.1 to 0.3 wt % of Zr, quenching the cast product at a temperature of 30° C. or less after the solutionizing, and aging the cast product after the quenching. 
     The solutionizing may be performed at a temperature ranging from 520° C. to 560° C. for 4 to 48 hours. 
     The aging may include primary aging and secondary aging after the primary aging so as to be performed twice. 
     The primary aging may be performed at a temperature ranging from 165° C. to 195° C. for 4 to 48 hours. 
     The secondary aging may be performed at a temperature ranging from 200° C. to 225° C. for 3 to 7 hours. 
     In accordance with another embodiment of the present disclosure, there is provided a method of manufacturing aluminum alloy, which includes solutionizing a cast product made of an aluminum alloy containing 0.1 to 0.3 wt % of Zr, quenching the cast product after the solutionizing, and aging the cast product after the quenching, wherein the aging includes primary aging and secondary aging after the primary aging so as to be performed twice. 
     The primary aging may be performed at a temperature ranging from 165° C. to 195° C. for 4 to 48 hours. 
     The secondary aging may be performed at a temperature ranging from 200° C. to 225° C. for 3 to 7 hours. 
     In accordance with a further embodiment of the present disclosure, there is provided an aluminum alloy that includes Al as a base material, 6.5 to 7.5 wt % of Si, 0.35 to 0.45 wt % of Mg, and 0.1 to 0.3 wt % of Zr. 
     The aluminum alloy may further include 0.2 wt % or less of Cu. 
     An Al 3 Zr precipitation-strengthening phase may be formed in the aluminum alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a heat treatment process of a conventional alloy. 
         FIG. 2  illustrates a heat treatment process of an alloy for cylinder heads according to an embodiment of the present disclosure. 
         FIG. 3  illustrates that an acicular Zr crystal appears in the alloy of the present disclosure. 
         FIG. 4  illustrates a result of measurement of cylinder head residual stress when an alloy is conventionally quenched. 
         FIGS. 5A and 5B  illustrate a crystallization phase when the alloy is quenched at a temperature of 80° C. and a crystallization phase when the alloy is quenched at a temperature of 30° C., respectively, in the present disclosure. 
         FIGS. 6A and 6B  illustrate a thermodynamic simulation result according to the addition Zr. 
         FIG. 7  illustrates a precipitation phase when heat treatment is performed on the alloy of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The accompanying drawings for illustrating exemplary embodiments of the present disclosure should be referred to in order to gain a sufficient understanding of the present disclosure, the merits thereof, and the objectives accomplished by the implementation of the present disclosure. 
     In the exemplary embodiments of the present disclosure, techniques well known in the art or repeated descriptions may be reduced or omitted to avoid obscuring appreciation of the disclosure by a person of ordinary skill in the art. 
       FIG. 2  illustrates a heat treatment process of an alloy for cylinder heads according to an embodiment of the present disclosure. 
     A method of manufacturing aluminum alloy and an aluminum alloy produced thereby according to exemplary embodiments of the present disclosure will be described below with reference to  FIG. 2 . 
     The present disclosure relates to a composition and manufacturing method of an alloy for cylinder heads capable of realizing high-temperature physical properties and high thermal conductivity to withstand the physical and thermal loads of a high-power engine. 
     The comparison between the composition of the aluminum alloy according to the present disclosure and the composition of the alloy according to the related art is indicated in the following table, and the aluminum alloy is prepared by T6 heat treatment illustrated in  FIG. 2 , unlike that illustrated in  FIG. 1 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Composition 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Cu 
                 Si 
                 Mg 
                 Zr 
                   
               
               
                   
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 Al 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Related Art 
                 0.2 or less 
                 6.5~7.5 
                 0.35~0.45 
                 — 
                 REM. 
               
               
                 (AC4CH) 
               
               
                 Present 
                 0.2 or less 
                 6.5~7.5 
                 0.35~0.45 
                 0.1~0.3 
                 REM. 
               
               
                 Disclosure 
               
               
                 (AC4CH—Zr) 
               
               
                   
               
            
           
         
       
     
     The aluminum alloy according to the present disclosure contains 0.1 to 0.3 wt % of Zr. 
     When the Zr content of the aluminum alloy exceeds 0.3 wt %, a coarse acicular Zr-related crystallization phase begins to appear, which is adversely affects the physical properties of the alloy. Therefore, the Zr content is limited to 0.1 to 0.3 wt %. 
     The aluminum alloy may further include Sr, Mn, Ti, and the like. 
     The aluminum alloy of the present disclosure has the above compositions shown in Table 2, and a cylinder head cast from the alloy is heat-treated to secure physical properties. In particular, examples of the product cast from the alloy may include not only a cylinder head that requires high-temperature physical properties, but also a component that requires similar properties. 
     The heat treatment includes solutionizing, quenching, primary aging, and secondary aging. 
     The solutionizing is performed at a temperature ranging from 520° C. to 560° C. for 4 to 48 hours. As a preferable example, the drawing illustrates that the solutionizing is performed at a temperature of 535° C. for 6 hours. 
     Unlike the related art, the quenching is performed at a temperature of 30° C. or less. 
     The primary aging is performed at a temperature ranging from 165° C. to 195° C. for 4 to 48 hours. As a preferable example, the drawing illustrates that the primary aging is performed at a temperature of 180° C. for 6 hours. 
     Unlike the related art, the present disclosure further includes the secondary aging. That is, the secondary aging is performed at a temperature ranging from 200° C. to 225° C. for 3 to 7 hours. As a preferable example, the drawing illustrates that the secondary aging is performed at a temperature of 215° C. for 6 hours. 
     In the AC4CH—Zr alloy of the present disclosure, an Al 3 Zr precipitation-strengthening phase is formed during the aging. Since the precipitation phase is effectively formed at a temperature of 200° C. or more that is higher than the existing Mg 2 Si precipitation-strengthening phase, additional aging is performed on the AC4CH—Zr alloy. 
     Meanwhile, a fine acicular Al 3 Zr crystallization phase is formed even in the composition of Zr in an amount of 0.3 wt % or less, which causes deterioration in physical properties. In order to prevent this physical property deterioration, the quenching is performed at a temperature of 30° C. or less after the solutionizing in the present disclosure. 
     Tables 3 and 4 summarize a test result for physical properties according to the amount of Zr in the alloy composition of the present disclosure. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Solutionizing: 535° C./6 hrs + Aging: 185° C./6 hrs 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 AC4CH 
                 +Zr 0.007 
                 +Zr 0.02 
                 +Zr 0.05 
                 +Zr 0.1 
                 +Zr 0.15 
               
               
                 Alloy Composition 
                 Alloy 
                 wt % 
                 wt % 
                 wt % 
                 wt % 
                 wt % 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Hardness (HB) 
                 94.5 
                 92.5 
                 90 
                 90.5 
                 86 
                 84 
               
               
                 Elongation (%) 
                 5.5 
                 4.14 
                 4.11 
                 4.6 
                 8.8 
                 8.31 
               
               
                 Yield Strength (MPa) 
                 236 
                 222 
                 229 
                 235 
                 210 
                 210 
               
               
                 Tensile Strength (MPa) 
                 293 
                 284 
                 289 
                 289 
                 272 
                 271 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Solutionizing: 535° C./6 hrs + Aging: 170° C./6 hrs 
               
            
           
           
               
               
            
               
                   
                 Alloy Composition 
               
            
           
           
               
               
               
               
               
            
               
                   
                 AC4CH 
                 +Zr 0.015 
                 +Zr 0.3 
                 +Zr 1.0 
               
               
                   
                 Alloy 
                 wt % 
                 wt % 
                 wt % 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Hardness (HB) 
                 99 
                 99 
                 99 
                 94 
               
               
                 Elongation (%) 
                 3.11 
                 6.46 
                 6.13 
                 0.68 
               
               
                 Yield Strength (MPa) 
                 244 
                 248 
                 249 
                 232 
               
               
                 Tensile Strength (MPa) 
                 288 
                 302 
                 300 
                 240 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 3, when 0.1 wt % or more of Zr is added to the alloy, the elongation of the alloy significantly increases. However, it can be seen that the alloy is decreased in hardness, yield strength, and tensile strength at room temperature, in inverse proportion to elongation. 
     In addition, when the aging condition is changed to prevent the deterioration of physical properties at room temperature, the alloy shows that an increment in elongation is decreased but strength properties are increased. 
     However, when the Zr content of the alloy exceeds 0.3 wt %, a coarse acicular Zr-related crystallization phase begins to appear as illustrated in  FIG. 3 , which is adversely affects the physical properties of the alloy. Therefore, the Zr content is preferably from 0.1 to 0.3 wt %. 
     In the heat treatment application of  FIG. 2  according to the present disclosure, a physical property evaluation result for each Zr component is indicated in the following Table 5. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                 +Zr 0.05 
                 +Zr 0.1 
                 +Zr 0.15 
                 +Zr 0.3 
                 +Zr 0.5 
                 +Zr 1.0 
               
               
                 Alloy Composition 
                 AC4CH 
                 wt % 
                 wt % 
                 wt % 
                 wt % 
                 wt % 
                 wt % 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Elongation (%) 
                 6.3 
                 6.7 
                 8.6 
                 9.2 
                 8.8 
                 3.3 
                 0.68 
               
               
                 Tensile Strength 
                 273 
                 269 
                 268 
                 270 
                 267 
                 254 
                 190 
               
               
                 (MPa) at Room 
               
               
                 Temperature 
               
               
                 Tensile Strength 
                 125 
                 128 
                 141 
                 144 
                 145 
                 121 
                 115 
               
               
                 (MPa) at High 
               
               
                 Temperature (250° C.) 
               
               
                   
               
            
           
         
       
     
     A quenching temperature will be described below in more detail. 
     In the heat treatment process of the conventional alloy for cylinder heads, the quenching temperature is essential to be maintained at 80° C. or more. Since the cylinder head has a complicated internal structure, residual stress is apt to occur according to the cooling rate for each part in the cylinder head. In fact, the cylinder head may be damaged by the residual stress at the time of development. Therefore, as can be seen in  FIG. 4 , the quenching condition should be changed from water cooling to air cooling. 
     However, when the alloy of the present disclosure is quenched at a temperature of 80° C. or more, a fine acicular Zr phase is crystallized as illustrated in  FIG. 5A . In this case, when 0.3 wt % or more Zr is added to the alloy, the effect of improving the physical properties of the alloy is inferior though the physical properties of the alloy are not considerably decreased compared to when the coarse crystallization phase appears. 
     However, when the quenching is performed at a temperature of 30° C. or less as in the heat treatment method of the present disclosure, the Zr-related crystallization phase becomes fine and is changed in shape from acicular to spherical as illustrated in  FIG. 5B , so that the physical properties of the alloy can be improved. 
     A change in physical properties according to the change of Zr crystallization phase may be referred to in the following Table 6. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Shape of Crystal- 
                 Yield Strength at 
                 Tensile Strength at 
                   
               
               
                 lization Phase 
                 Room Temperature 
                 Room Temperature 
                 Elongation 
               
               
                   
               
             
            
               
                 Acicular 
                 244 
                 289 
                 4.4 
               
               
                 Spherical 
                 247 
                 301 
                 6.2 
               
               
                   
               
            
           
         
       
     
     The term “crystallization phase” refers to a phase in which particles, which have not dissolved beyond the solid solution limit when molten Al is cooled, remain in the Al matrix. Generally, the crystallization phase may be observed when a material structure is analyzed using an optical microscope and an SEM. As a result of the Jmatpro thermodynamic simulation of  FIGS. 6A and 6B , when Zr is added in an amount of 0.05 wt %, the solid solution of Zr reaches a threshold at a temperature of 476° C. or less so that a Zr-related phase begins to be crystallized. That is, when Zr is added in an amount of 0.05 wt %, the Zr-related phase is not crystallized at 650° C. or more, which is a temperature at which casting is generally performed. On the other hand, when Zr is added in an amount of 0.25 wt %, the solid solution of Zr reaches a threshold at 649° C. so that there is a sufficient possibility that a crystallization phase remains during cooling. This crystallization phase has an effect of strengthening materials by physically obstructing potential movement, but it rather weakens the physical properties of materials by acting as a stress concentration point when an acicular crystal is formed. 
     The term “precipitation phase” refers to a phase in which particles dissolved in molten Al exist in a supersaturated solid solution state due to quenching and are later precipitated into a solid by heat treatment. The crystallization phase is formed during solidification whereas the precipitation phase is formed during heat treatment (solutionizing+aging). Since the precipitation phase is fine enough not to be seen in general structure observation, it can be seen through TEM observation as illustrated in  FIG. 7 . 
     Furthermore, in the present disclosure, the secondary aging is performed after the quenching is performed at 30° C. or less and the primary aging is then performed. 
     If only the primary aging is conventionally performed in spite of the optimal composition of Zr, it can be seen that the treatment may not satisfy desired physical properties, namely all of high elongation, high thermal conductivity, and high-temperature durability. 
     This is due to the crystallization of acicular Zr structures and the absence of Zr-related precipitation-strengthening phases. The Mg 2 Si precipitation phase, which is a strengthening phase of the existing AC4CH alloy, shows an optimum precipitation-strengthening effect when aging is performed at 180° C. for 6 hours, whereas Al 3 Zr, which is a Zr-related precipitation phase, is precipitated into a matrix at a higher temperature to exhibit a strengthening effect. Accordingly, after the Mg 2 Si precipitation phase is distributed in the matrix by performing aging at 160 to 195° C. for 4 to 24 hours, the secondary aging is further performed. Since the Mg 2 Si precipitation phase begins to lose a strengthening phase effect when exposed to a high temperature of 200° C. or more, additional aging temperature and time are required to obtain the Al 3 Zr precipitation phase, which is a high-temperature strengthening phase, while minimizing the effect degradation of the Mg 2 Si precipitation phase. 
     The effects of strengthening phases are tested through physical property measurement, and the following Table 7 summarizes a result of the test. Table 7 indicates results when the secondary aging is performed at 200 to 225° C. for 3 to 7 hours under the conditions that the solutionizing is performed at 535° C. for 6 hours, the quenching is performed at 30° C., the primary aging is performed at 180° C. for 6 hours. In particular, as the result of additional aging at 215° C. for 6 hours, it can be seen that the strength properties at room temperature are slightly decreased due to the loss of Mg 2 Si strengthening effect, but the strength properties at high temperature are improved due to the effect of Al 3 Zr acting as a high-temperature strengthening phase. 
     In addition, performing the secondary aging can resolve the residual stress caused by the quenching at room temperature and obtain high elongation and high thermal conductivity by strength decreased at room temperature. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                   
                   
                 Yield 
                 Tensile 
                 Yield 
                 Tensile 
                   
                   
               
               
                 Secondary 
                   
                   
                 Strength 
                 Strength 
                 Strength 
                 Strength 
               
               
                 Aging 
                 Secondary 
                   
                 at Room 
                 at Room 
                 at High 
                 at High 
                   
                 Thermal 
               
               
                 Temperature 
                 Aging 
                 Hardness 
                 Temperature 
                 Temperature 
                 Temperature 
                 Temperature 
                 Elongation 
                 Conductivity 
               
               
                 (° C.) 
                 Time (h) 
                 (HB) 
                 (MPa) 
                 (MPa) 
                 (MPa) 
                 (MPa) 
                 (%) 
                 (W/m · K) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                  99~102 
                 247 
                 301 
                 116 
                 125 
                 6.2 
                 155 
               
               
                 180 
                 6 
                 100  
                 247 
                 296 
                 111 
                 120 
                 6.1 
                 154 
               
               
                 180 
                 12 
                 96 
                 244 
                 297 
                 117 
                 122 
                 6.6 
                 156 
               
               
                 180 
                 24 
                 92 
                 236 
                 276 
                 119 
                 127 
                 6.8 
                 157 
               
               
                 215 
                 3 
                 81~87 
                 229 
                 275 
                 126 
                 141 
                 8.4 
                 167 
               
               
                 215 
                 6 
                 79~86 
                 229 
                 272 
                 128 
                 146 
                 9.3 
                 169 
               
               
                 245 
                 6 
                 55~65 
                 110 
                 149 
                 97 
                 109 
                 12 
                 159 
               
               
                   
               
            
           
         
       
     
     As described above, it can be seen that the alloy of the present disclosure including Zr in the range has a tensile strength of about 272 MPa at room temperature and a tensile strength of about 146 MPa at high temperature as illustrated in Table 7. However, it can be seen that the alloy does not have desired physical properties when each heat treatment condition is not satisfied as illustrated in the following Table 8. Therefore, it is possible to derive optimum heat treatment conditions as illustrated in Table 9. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                 Condition of Process 
                   
                   
               
               
                 Process 
                 Dissatisfaction 
                 Result (unit: MPa) 
                 Remark 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Solutionizing 
                 Temperature 
                 Min 
                 Tensile Strength at Room 
                 Process 
               
               
                   
                   
                 Value 
                 Temperature: 189 
                 Temperature: 505° C. 
               
               
                   
                   
                 Max 
                 Part Shape/Dimension 
                 Process 
               
               
                   
                   
                 Value 
                 Damage 
                 Temperature: 570° C. 
               
               
                   
                 Time 
                 Min 
                 Tensile Strength at Room 
                 Time: 3 hrs 
               
               
                   
                   
                 Value 
                 Temperature: 194 
               
               
                   
                   
                 Max 
                 Part Shape/Dimension 
                 Time: 50 hrs 
               
               
                   
                   
                 Value 
                 Damage 
               
            
           
           
               
               
               
               
            
               
                 Quenching 
                 More than 30° C. 
                 Deterioration of Physical 
                 See Table 6 
               
               
                   
                   
                 Properties by Acicular Zr 
               
               
                   
                   
                 Crystallization Phase 
               
            
           
           
               
               
               
               
               
            
               
                 Primary 
                 Temperature 
                 Min 
                 Tensile Strength at Room 
                 Process 
               
               
                 Aging 
                   
                 Value 
                 Temperature: 217 
                 Temperature: 155° C. 
               
               
                   
                   
                 Max 
                 Tensile Strength at Room 
                 Process 
               
               
                   
                   
                 Value 
                 Temperature: 166 
                 Temperature: 200° C. 
               
               
                   
                 Time 
                 Min 
                 Tensile Strength at Room 
                 Time: 3.5 hrs 
               
               
                   
                   
                 Value 
                 Temperature: 216 
               
               
                   
                   
                 Max 
                 Tensile Strength at Room 
                 Time: 60 hrs 
               
               
                   
                   
                 Value 
                 Temperature: 223 
               
               
                 Secondary 
                 Temperature 
                 Min 
                 Tensile Strength at Room 
                 Process 
               
               
                 Aging 
                   
                 Value 
                 Temperature: 277 
                 Temperature: 195° C 
               
               
                   
                   
                   
                   
                 Expected Residual 
               
               
                   
                   
                   
                   
                 Stress Occurrence 
               
               
                   
                   
                 Max 
                 Tensile Strength at Room 
                 Process 
               
               
                   
                   
                 Value 
                 Temperature: 149 
                 Temperature: 245° C. 
               
               
                   
                 Time 
                 Min 
                 Tensile Strength at Room 
                 Time: less than 3 
               
               
                   
                   
                 Value 
                 Temperature: 275 
                 hrs 
               
               
                   
                   
                   
                   
                 Expected Residual 
               
               
                   
                   
                   
                   
                 Stress Occurrence 
               
               
                   
                   
                 Max 
                 Tensile Strength at Room 
                 Time: 8 hrs 
               
               
                   
                   
                 Value 
                 Temperature: 164 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 9 
               
             
            
               
                   
                   
               
               
                   
                 Temperature 
                   
                   
               
               
                   
                 (° C.) 
                 Time (h) 
                 Critical Significance of 
               
            
           
           
               
               
               
               
               
               
            
               
                 Process 
                 Min 
                 Max 
                 Min 
                 Max 
                 Heat Treatment Condition 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Solution- 
                 520 
                 560 
                 4 
                 48 
                 Dissolved into Reinforcing 
               
               
                 izing 
                   
                   
                   
                   
                 Element Al as Base Material 
               
               
                 Quenching 
                 — 
                 30 
                 — 
                 — 
                 Spheroidizing of Al 3 Zr 
               
               
                   
                   
                   
                   
                   
                 Crystallization Phase 
               
               
                 Primary 
                 165 
                 195 
                 4 
                 24 
                 Formation of Mg 2 Si 
               
               
                 Aging 
                   
                   
                   
                   
                 Precipitation Phase 
               
               
                 Secondary 
                 200 
                 225 
                 3 
                  7 
                 Formation of Al 3 Zr 
               
               
                 Aging 
                   
                   
                   
                   
                 Precipitation Phase 
               
               
                   
               
            
           
         
       
     
     As described above, the alloy according to the present disclosure can exhibit the following effects as illustrated in the following Table 10. 
     The alloy is increased by 50% in elongation and 10% in thermal conductivity at room temperature, compared to existing materials. Although the alloy is somewhat decreased in strength properties (hardness: HB93→HB 78) at room temperature, it is increased in strength properties at the high temperature at which the engine is driven, for example, by 11% in yield strength and 17% in tensile strength, compared to existing materials. Overall, the alloy is increased by 30% or more in fatigue strength at a high temperature due to the increase in elongation, yield strength, and tensile strength. In addition, when the thermal conductivity of the cylinder head is increased by 10%, the torque of the engine is increased to result in an improvement in performance, which also helps to reduce knocking and thus improve fuel efficiency. 
     Furthermore, the current process in which quenching is performed at a temperature of 80° C. or more to reduce residual stress incurs the cost of maintaining water at a high temperature and the cost of excessive evaporation of water, whereas the present disclosure is expected to achieve a reduction in cost since quenching is performed at a temperature of 30° C. or less, compared to the related art. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 Alloy of 
                 Alloy of Present 
               
               
                   
                 Related Art 
                 Disclosure 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Alloy 
                 AC4CH 
               
            
           
           
               
               
               
            
               
                 Added Element 
                 None 
                 0.2 wt % of Zr 
               
               
                 Heat Treatment 
                 Solutionizing: 535° C./ 
                 Solutionizing: 535° C./ 
               
               
                   
                 6 hrs + Aging: 180° C./ 
                 6 hrs + Aging: 180° C./ 
               
               
                   
                 6 hrs 
                 6 hrs + Aging: 215° C./ 
               
               
                   
                   
                 6 hrs 
               
               
                 Hardness at Room 
                 HB 93 
                 HB 78 
               
               
                 Temperature 
               
            
           
           
               
               
               
               
               
            
               
                 Yield Strength 
                 115 
                 MPa 
                 128 MPa 
                 (11%↑) 
               
               
                 (@ 250° C.) 
               
               
                 Tensile Strength 
                 125 
                 MPa 
                 146 MPa 
                 (17%↑) 
               
               
                 (@ 250° C.) 
               
            
           
           
               
               
               
               
            
               
                 Elongation (Room 
                 5.5% 
                 9.30% 
                 (50%↑) 
               
               
                 Temperature) 
               
            
           
           
               
               
               
               
               
            
               
                 Thermal 
                 154 
                 W/m · K 
                 169 W/m · K 
                 (10%↑) 
               
               
                 Conductivity 
               
               
                   
               
            
           
         
       
     
     In accordance with exemplary embodiments of the present disclosure, the aluminum alloy can be applied to the cylinder head of the high-power engine by having excellent high-temperature physical properties and high thermal conductivity in favor of performance and fuel efficiency. 
     More specifically, the aluminum alloy is increased by 50% in elongation and 10% in thermal conductivity at room temperature, compared to existing materials. Although the aluminum alloy is somewhat decreased in strength properties (hardness: HB93→HB 78) at room temperature, it is increased in strength properties at the high temperature at which the engine is driven, for example, by 11% in yield strength and 17% in tensile strength, compared to existing materials. Overall, the aluminum alloy is increased by 30% or more in fatigue strength at a high temperature due to the increase in elongation, yield strength, and tensile strength. In addition, when the thermal conductivity of the cylinder head is increased by 10%, the torque of the engine is increased to result in an improvement in performance, which also helps to reduce knocking and thus improve fuel efficiency. 
     Furthermore, the current process in which quenching is performed at a temperature of 80° C. or more to reduce residual stress incurs the cost of maintaining water at a high temperature and the cost of excessive evaporation of water, whereas the present disclosure is expected to achieve a reduction in cost since quenching is performed at a temperature of 30° C. or less, compared to the related art. 
     While the specific embodiments have been described with reference to the drawings, the present disclosure is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure as defined in the following claims. Therefore, these changes and modifications will fall within the scope of the disclosure as long as they are apparent to those skilled in the art, and the scope of the present disclosure should be defined based on the entire content set forth in the appended claims.