Study On Microstructure And Properties Of Al-3.2Mg-xZn-1.12Cu-yTi Aluminum Alloy And Reinforced Composites Of SiC_w By Extrusion Casting

Al-Zn-Mg-Cu series aluminum alloy has excellent characteristics such as high strength and low density.In many countries,it is widely used in the manufacture of military equipment and spacecraft.The composite material prepared with Al-Zn-Mg-Cu series aluminum alloy as the matrix not only has higher strength,but also has the advantages of high elastic modulus and high temperature resistance.This article aims to study the effects of Zn/Mg ratio（3.56,3.72,3.87）,Ti element content（0wt%,0.39wt%,0.87wt%）,extrusion ratio（10:1,16:1）and aging process（T6:121℃×24h,T6I6:121℃×2h（cold water）+65℃×56h+121℃×16h,RRA:121℃×24h+170℃×2h+121℃×24h）on the mechanical properties and microstructure of Al-Zn-Mg-Cu series aluminum alloy.The self-melting aluminum alloy is used as the matrix to explore the process for the preparation of composite materials by liquid-phase squeeze casting;the aluminum matrix composite material reinforced with SiC_w is used to explore the effect of different aging processes（T6-1:121℃×5h,T6-2:121℃×2.5h,T6I4:121℃×4h（cold water）+65℃×56h,T6I4-1:121℃×2h（cold water）+65℃×56h）on the mechanical properties of the composite material.（1）In the experiment,the Zn/Mg ratio of the aluminium alloy is 3.56,3.72 and3.87 respectively.When the Zn/Mg ratio is 3.56,the degree of grain refinement is obvious,and a higher hardness of 226.6HV can be obtained.However,as the Zn/Mg ratio continues to increase,the dislocation and hardness of the alloy decrease.In this experiment,the content of Ti element was 0wt%,0.39wt%,0.87wt%.When the Ti content increases from 0wt%to 0.87wt%,the grain size of alloy tends to decrease after increasing,whose corrosion ability is also improved.The depth of intergranular corrosion is reduced to 141.07μm,when Ti is 0.39wt%;The extrusion ratio was respectively 10:1 and 16:1,the grain size of the alloy with large extrusion ratio was smaller,and the ultimate solid solution temperature of the matrix decreased.Two-stage aging of T6I6 generally improves the hardness and room-temperature tensile strength of the alloy,the maximum tensile strength can reach 716.77MPa.RRA aging process improves the alloy’s corrosion resistance and elongation,the elongation can reach more than 7.0%.（2）Aluminum matrix composites with SiC_w,SiC_w+SiC_p and SiC_w+CNT_s as reinforcing materials were prepared by extrusion casting process.The forming effect of prefabricated parts prepared with Na₂SiO₃ and AlPO₄ of specific concentration as binder is good,which has both low-temperature strength and high-temperature strength.The compressive strength of the whisker SiC_w reinforced preform is 19.24MPa.Prolonging the ultrasonic oscillation time can improve the molding rate of the prefabricated parts mixed with SiC_w,SiC_w+SiC_p and SiC_w+CNT_s.In the forming process of composite materials produced by squeeze casting,SiC_w and SiC_w+CNT_s hybrid preforms and composites had high molding rates and good molding effects,with densities up to 97%and 98%,respectively.（3）The grain refinement effect of SiC_w reinforced aluminum matrix composites prepared by squeeze casting is obvious,the undissolved phase is reduced,and the dislocation contribution strength reaches 91.40MPa.The aging process in the experiment is divided into single-stage aging（T6-1,T6-2）and two-stage aging（T6I4,T6I4-1）.With the increase of composite hardness after aging,the conductivity decreases regularly.The hardness of T6I4-1 reached the highest of 345.8HV and the conductivity reached the lowest of 11.7IACS%.The optimum aging process of the composite was T6-2:12 1℃×2.5h,whose compressive strength were increased to746.42MPa and compressive fracture toughness were increased to 7.0%.In summary,in the process of aluminum alloy research,the high-strength aluminum alloy with tensile strength up to 716.77MPa was prepared by adjusting the alloy composition,changing the extrusion ratio,and combining with different aging processes,and the aluminum alloy with good intergranular corrosion resistance and elongation increased to more than 7.0%was also obtained.In the research process of aluminum matrix composites,by extrusion casting method combined with different aging processes,high-hardness SiC_w whisker reinforced aluminum matrix composites with a hardness of 345.8HV were prepared,and high-strength and high-strain SiC_w whisker reinforced aluminum matrix composites with a compressive strength of746.42MPa and compressive fracture strain of 7.0%were also prepared.The above findings are rarely reported in domestic and foreign studies.