Since the magnesium-lithium-based alloy is very active, in order to prevent the alloy from oxidative burning during melting, alloy smelting is performed in an upper sealed metal crucible, and high-purity argon is continuously blown into the upper portion of the crucible for protection. Vacuum impregnation method was used to prepare composites. The reinforcing body is a B-type SiC whisker produced by Japan East Sea Carbon Corporation. First, a SiC whisker preform is prepared by a vacuum suction filtration method. The volume content of the SiC whisker is 13%; then, the SiC whisker preform and the MgL-iAl alloy material are put into a special mold and put into a vacuum. Immersion furnace heating. After the alloy is melted, the alloy is hydraulically forced into the SiC whisker preform at a pressure of 740 to 760 e using a high-purity argon gas of 8 MPa to obtain a SiCw/MgLiAl composite material.
The microstructure of the composite was observed by JSM-6400 scanning electron microscope. The interface structure of the composite was observed by H-800 transmission electron microscope and H-9000 high-resolution electron microscope. The ion thinning method was used for the samples observed by transmission electron microscopy and high-resolution electron microscopy.
The interface between the SiC whisker and the base alloy is very smooth and without any reactants. Using high-resolution electron microscopy to observe the interface of the composite material, it was found that the interface between the SiC whisker and the matrix alloy is well-bonded and there is no reaction product. It shows that although the SiC whiskers and the matrix alloy elements are thermodynamically reacted, due to the low reaction driving force or the slow reaction speed, no interface reaction occurs under the experimental conditions. In addition, it can also be seen from FIG. 3 that a disordered transition region of atoms is present in the base alloy near the interface. This is due to the difference in thermal expansion coefficient between the SiC whiskers and the base alloy. The thermal expansion coefficient of the SiC whisker is 4.18×10-6, and the thermal expansion coefficient of the MgLi8Al1 alloy is determined to be 3.03×10-5. It can be seen that the thermal expansion coefficient of the substrate alloy is significantly larger than that of the SiC whisker. Therefore, during the cooling process, the composite material generates a large internal stress at the interface between the matrix alloy and the SiC whisker, which causes a disordered transition region of the matrix alloy atoms near the interface. The presence of an atomic disorder in the transition zone near the interface further indicates that the composite has a good interface.
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