a molten metal of each aluminum alloy shown in fig1 ( examples 1 to 13 ) and a molten metal of each aluminum alloy shown in fig2 ( comparative examples 1 to 28 ) were prepared , and cast into a billet . note that the content ( mass %) of each component shown in fig1 and 2 indicates the analytical value after casting . fig3 and 4 show the billet homogenization temperature ( homo temperature ), the extrusion conditions , and the evaluation results . fig3 and 4 show the optimum ranges of the homo temperature and the extrusion conditions , and each data indicates the measured value . in fig3 and 4 , the billet temperature refers to the billet preheating temperature before extrusion , and the temperature of the extruded shape refers to the surface temperature of the extruded shape measured immediately after extrusion . the cooling rate after extrusion refers to the cooling rate until the temperature of the extruded shape reached 200 ° c . or less when air was blown against the extruded shape using a fan immediately after extrusion . scc refers to the stress corrosion cracking resistance . the stress corrosion cracking resistance was evaluated as described below . specifically , an accelerated test was performed by immersing a sample ( to which a stress equal to 80 % of the proof stress was applied ) in a 3 . 5 % nacl aqueous solution at 25 ° c . for 10 minutes , and allowing the sample to dry at a temperature of 25 ° c . ( room temperature ) and a humidity of 40 % for 50 minutes (= 1 cycle ). when stress corrosion cracking was not observed after 720 cycles , it was determined that the sample had stress corrosion cracking resistance sufficient for a structural material ( e . g ., bumper reinforcement ). in fig3 and 4 , σ b refers to tensile strength , σ 0 . 2 refers to proof stress , and δ refers to elongation . these mechanical properties were measured using a jis z 2241 no . 5 specimen that was cut from the extruded shape . the recrystallization ratio in the microstructure was determined by observing the cross section orthogonal to the extrusion direction using a microscope , and calculating the area ratio of the recrystallization area . the extrudability was determined to be normal when a surface defect having a depth of 0 . 5 mm or more was not observed when an extruded shape having the cross - sectional shape illustrated in fig5 to 7 was extruded , and the presence or absence of a surface defect ( tearing or pickup ) having a depth of 0 . 5 mm or more was evaluated . in examples 1 to 13 , a proof stress of 470 mpa or more that is necessary for achieving a reduction in weight of a bumper reinforcement and the like was obtained , and excellent stress corrosion cracking resistance was achieved . in comparative examples 1 and 2 in which the homo temperature was more than 560 ° c ., the billet was locally melted to only a small extent , and could be extruded . however , since the amount of precipitates produced during homogenization was small , and recrystallization of the extruded shape could not be suppressed , the stress corrosion cracking resistance deteriorated . in comparative examples 3 , 5 , 8 , 10 to 15 , and 20 , since the mg content was less than 1 . 6 %, a proof stress of 470 mpa or more could not be obtained . in comparative examples 16 and 25 , since the zn content was more than 7 . 0 %, the stress corrosion cracking resistance deteriorated . in comparative examples 4 and 6 in which the mg content was less than 1 . 6 %, and the zn content was more than 7 . 0 %, the desired strength was obtained , but the stress corrosion cracking resistance deteriorated . in comparative example 7 , since the zn content was less than 6 . 0 %, the desired strength could not be obtained . in comparative example 9 , since the cooling rate after extrusion was less than 50 ° c ./ min , the desired strength could not be obtained . in comparative examples 17 and 18 in which the homo temperature did not fall within the optimum range , the desired strength could not be obtained when the homo temperature was lower than the optimum range , and the billet was locally melted , and could not be extruded when the homo temperature was higher than the optimum range . in comparative example 19 , since the mg content was less than 1 . 6 %, and the cooling rate after extrusion was less than 50 ° c ./ min , the desired strength could not be obtained . in comparative example 21 , since the mg content was less than 1 . 6 %, the desired strength could not be obtained . moreover , since the total content of mn , cr , and zr was less than 0 . 15 %, recrystallization of the extruded shape could not be suppressed , and the stress corrosion cracking resistance deteriorated . in comparative example 22 , since the mg content was less than 1 . 6 %, the desired strength could not be obtained . moreover , since water cooling was performed after extrusion , the cooling rate exceeded 500 ° c ./ min , and the material became brittle due to incorporation of hydrogen . as a result , the stress corrosion cracking resistance deteriorated . in comparative examples 23 and 24 , since the temperature of the extruded shape was higher than 585 ° c ., pickup or tear occurred on the surface of the extruded profile . in comparative example 26 , since the mg content was less than 1 . 6 %, the desired strength could not be obtained . moreover , since the zn content was more than 7 . 0 %, sufficient stress corrosion cracking resistance could not be obtained . in comparative examples 27 and 28 , since the mg content was less than 1 . 6 %, the desired strength could not be obtained . moreover , since the total content of mn , cr , and zn was less than 0 . 15 %, recrystallization of the extruded shape could not be suppressed , and the stress corrosion cracking resistance deteriorated . the aluminum alloy according to the embodiments of the invention exhibits excellent extrudability , and makes it possible to produce an extruded shape having the cross - sectional shape illustrated in fig5 to 7 . fig5 illustrates an example of an extruded shape having a triple - hollow cross - sectional shape that is used for a bumper reinforcement and the like . when the dimension a is more than 40 mm and 75 mm or less , and the dimension b is 120 mm or less , it is possible to produce an extruded shape wherein 3 ≦ t 1 ≦ 8 , 1 ≦ t 2 ≦ 6 , 1 ≦ t 3 ( t 31 , t 32 , . . . )≦ 6 . the extrudable dimensional range is similarly shown in fig6 and 7 . a high - strength extruded shape exhibiting excellent stress corrosion cracking resistance can be obtained using the aluminum alloy according to the embodiments of the invention . the extruded shape may be applied to a vehicular structural member and the like .