| Al-Zn-Mg-Cu aluminum alloy and its composite materials have become one of the most widely used materials in aerospace,military defense and other fields because of the excellent comprehensive properties.In the experiment,Al-8.8Zn-2.2Mg-x Cu-0.1Sr-0.2Zr-y Ti was designed into four kinds of aluminum alloys.According to the results,the alloy material with best strength and toughness was selected as the matrix and combined with SiCw?SiCw+SiCp to parpare the aluminum matrix composites by reaction squeeze casting(RSC)method.The main research contents and results of the organization structure and performance analysis are as follows:(1)The effects of Ti element with a content gradient of 0,0.5(wt.%)and Cu element with a content gradient of 1.1,1.8 and 2.5(wt.%)on the structure and properties of aluminum alloys were studied.It was found that the addition of 0.5 wt.%Ti can almost eliminate the large-sized grains of 200?350?m,significantly refine the grain size and improve the size distribution.Meanwhile,the hardness and tensile strength of the alloy at room temperature increased,reaching up to 226.6HV and738.27MPa,while the elongation after fracture was 10.8%.When the Ti content remains unchanged,as the Cu content continues to increase,the effect of Ti element in refining the grain size began to be weakened.The hardness of the alloy began to decrease continuously,while the electrical conductivity increased significantly.At the same time,the tensile strength began to decline continuously.When the Cu content is 1.8 wt.%,the tensile strength began to decline slightly,but the elongation after fracture increased significantly,which is the highest among the four alloys,reaching 13.2%.When the Cu content continues to be added to 2.5 wt.%,the tensile properties will greatly reduce.The tensile strength was only 633.25MPa,and the elongation after fracture was only 7.0%left.The ability to resist intergranular corrosion also greatly reduced.Preliminarily,it is determined that Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti was used as the matrix of the aluminum matrix composite material.(2)The effects of T6,T6I4,T6I6 and RRA-T6I4 aging processes on the properties of Al-Zn-Mg-Cu aluminum alloys were studied.It can be found that the strength of the four alloys has little change compared with T6,but the elongation has significantly increased and especially for RRA-T6I4.For Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti,the order of the four aging processes in improving the properties of the alloy was as follows(">"means"be superior to"):In terms of strength:T6I4>T6>T6I6>RRA-T6I4.In terms of toughness:RRA-T6I4>T6I4>T6>T6I6.In terms of resistance to corrosion:RRA-T6I4>T6I4>T6I6>T6.According to the results,the strength and toughness of the alloy reached the optimal solution at T6I4,the tensile strength was748.61MPa,and the elongation after fracture was 13.2%.According to TEM,it is found that the strengthening phase precipitated in grains is very small and the degree of dispersion is also very high in T6I4 state.The GBPs size is 25?40nm and the PFZ width is about 30nm,which are significantly smaller than the GBPs size and PFZ width in T6state.The distribution of PFZ is discontinuous and the phase spacing is very significant.Finally,it is determined that Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti was used as the matrix of the aluminum matrix composite material.(3)The microstructure and properties of the Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti reinforced with SiCw,SiCw+SiCp were studied.The SiCw reinforced composite had poor interface bonding and the uniform distribution of reinforcements was not well.In the SiCw+SiCp reinforced composite material,the addition of SiCp significantly improved the uniformity and density of the reinforcement distribution,leading to the interface bonding of the composite material.Meanwhile,the SiCw+SiCp reinforced composite had better significant advantages on the dislocation density and dislocation strengthening than the SiCw reinforced composite,reaching 4.37×1014m-2and 114.17MPa,respectively.In the T6 peak aging state,the SiCw+SiCp reinforced composite was more effective than the SiCw reinforced composite in the hardness and compression strength,which reached up to 376.7HV and 889.7MPa,respectively,while the compression was 8.40%.For Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti+SiCw+SiCp,the optimum T6I4 aging process is 121?×1h(water cooling)+65?×36h,which of the compression strength arrived at 991.8MPa.In summary,a high strength and toughness aluminum alloy,as well as the aluminum matrix composite reinforced with SiCw+SiCp by RSC method has been successfully prepared in this paper.The Studies have shown that Al-8.73Zn-2.24Mg-1.21Cu-0.2Zr-0.1Sr-0.47Ti has outstanding tensile strength and toughness,and the optimum aging process is 121?×4h(water cooling)+65?×120h(T6I4).In addition,the SiCw+SiCp reinforced composite material has more advantages than SiCw reinforced composite in improving the structure,hardness and compressive performance.Meanwhile,the optimum T6I4 aging process is 121?×1h(water cooling)+65?×36h.At present,there are few studies on the preparation of multi-element hybrid reinforced composite materials and their aging process by liquid phase method and this article can provide relevant references for the subsequent research. |
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